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Thread: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

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    IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    I am quite late to the digital back's party, and so this might not be a news to you guys. I am quite shocked that the native base ISO is not at 50 for nomal mode, or 140 for long exposure mode. However I am sure I am not the last to know about this, so I think it is necessary to make a post. I have proofs below:



    As can be seen above for the case of normal mode, for the same lens at the same aperture, 50 ISO and 80 seconds has less highlight details recoverability than 100 ISO and 40 seconds.



    As can be seen above for the case of long exposure mode, for the same lens at the same aperture, 140 ISO and 20 seconds has less highlight details recoverability than 200 ISO and 14 seconds.

    For some reason, Phase One has chosen to not explicitly tell the truth that this Dalsa CCD is indeed working at 100 ISO voltage. If you work at 50 ISO, then the histogram and lightlight warning are NOT reliable! You end up risk blowing up your highlights without being aware of! (The same holds for 140 ISO in long exposure mode.)



    The ISO sensitivity test from dxomark also confirms that this is true for the IQ180 digital back.

    Further validating this, I have asked Bill Claff to run his algorithms on the IQ260 RAW files. (These test shots were taken at room temperature.) He got the following conclusions:

    Here are the normal mode results:
    50 9.99
    100 10.01
    200 8.99
    400 7.97
    800 7.00
    1600 6.83
    3200 5.82

    It's clear the base ISO is 100 since the ISO 50 result is the same.
    Things go normally from ISO 100 to ISO 800.
    At ISO 1600 "Sensor+" must kick in.
    I noticed the ISO 1600 and ISO 3200 files are also lower resolution; 4490x3364 versus 8984x6732

    The long exposure mode results are similar:
    140 9.18
    200 9.18
    400 8.20
    800 7.20
    1600 6.84
    3200 5.85
    It can also be seen that the Dalsa CCD can not keep up competitive against the latest SONY CMOS chips in terms of dynamic range performance (especially the ability to pull up shadows for long exposure shots).

    I am now quite torn between the IQ260 and the IQ250. One has ultra wide angle, while the other is much better at long exposure shots.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    I won't pretend to understand much of the above (although if someone could explain it all I'd be grateful), but on your last point, the IQ250 has ultra wide angle when you pair it with the Canon TS-E's and an ALPA FPS.

    Kind regards,

    Gerald.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    BTW - here's a set of IQ250 RAWs at all ISO's that you may use for further research (but no republishing anywhere).

    https://www.dropbox.com/sh/ddqeg3y5ofjbzm8/ZvptzNKUlH

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    I guess I don't follow. Shouldn't longer exposures, ISO 50 at 80sec vs. ISO 100 at 40 secs, fill the well capacity to a greater extent and therefore have a harder time with blownout highlights? ISO 100 is just underexposing.

    Sensor technology has been improving, both in terms of highlight and shadow detail. I would image an older sensor not doing as well as a newer one. But the trick is to find out its significance in the images you produce. If a scene falls into the DR, then it does not matter if another camera has more.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    I can't speak to the graphs/tests etc. I own a 260 and have used it extensively in the field since August 2013.

    I would feel it's safe to say the following to your questions.

    1. Only Phase One really knows what the base iso is, however I strongly feel it's 50, not 100. I base this on the fact that even moving from 50 to 100 creates a considerable amount of noise in the shadows. I base DR more on range, i.e how much can I get from a single shot.

    2. In regards to highlights, so far I have been dramatically impressed with the 260's ability to hold highlights, both at 50 and 200, non long exposure mode. I feel it's better than what I could get with the 160, considerably better. This became even more clearer to me after I started shooting tethered in the field (again thanks to Ken Doo's work). You can easily test a shot in C1 while tethered and realize just how much range you have, where on the LCD all you will see is the blinking highlight. Highlights in general, back to my P45+ days have always been tough. The 160 had more room, but on the shoots I have done in extreme lighting with the 260, I have been very pleased with the back's ability to hold detail in high lights that might be as much as .75 of a stop over exposed.

    3. No doubt, the 250 is going to give you more reach in the shadows, Doug from DT's library testing showed that. The 250 allowed for as much as 2.5 full stops of underexposure. You could pull this same area up and have full noise free details. Just like with a D800. (again at base iso 100). You can't get that with a CCD back, they love light, it's just that simple. They don't play well in low light situations, especially if you need faster shutter speeds. Again, with the 260 at base iso 50, you can pull up your shadows an impressive amount, say 1.5 stops in most cases, unless you are shooting an extreme shift with no CF. Then you may only get 1.0 stop or .75, but it will be clean. Push that to 200, and those shadows are worthless, totally. Thus the back required dual shooting at 50 and 200 if you are working in harsh light or with a lot of wind and you need to stop motion. In my world that is everyday. Sadly, I don't see any difference in long exposure mode 200, as the noise seems the same, here I had hoped for some Phase One magic, with the new chip, but so far, it has not happened, and I am starting to feel it isn't either At 140, you will get just a bit cleaner but it's still pretty noise ridden in shadows.

    4. The main downside to the 250, besides the extremely HARSH COST to upgrade from a less than 1 year old 260, is the fact that it's not seemingly friendly with wides on a tech solution. Torger has shown enough info that the 250 seems to have some crosstalk issues once you get to shifting past 5mm. I shift a lot and would need to test a 250 with my tech setup extensively. The fact that very litttle testing besides initial tests early on, with tech cameras has been is pretty telling. You also have to remember the 1.3 crop i.e. 30 percent of your sensor area is gone. Since I mainly shoot wides, this is a consideration that would weigh heavily for me.

    Paul

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by Paul2660 View Post
    1. Only Phase One really knows what the base iso is, however I strongly feel it's 50, not 100. I base this on the fact that even moving from 50 to 100 creates a considerable amount of noise in the shadows. I base DR more on range, i.e how much can I get from a single shot.
    Moving from 50 to 100 ISO should create more noise in the shadow only if you shorten the exposure time (and as a result of faster shutter speed, you gain more detail recoverability in the highlight, so the total DR remains the same.). If you use the same shutter speed (and aperture) for both 50 ISO and 100 ISO you should then be able to recover the same amount of highlight details while retaining the same amount of noise in the shadow. Actually these two are both working at 100 ISO voltage. The 50 ISO setting is just like the extended ISO settings in Canon and Nikon camera bodies, i.e. they shoot at 100 ISO then pull down 1-stop exposure in the camera. Thus, the histogram and highlight warnings at 50 ISO are not reliable, because what you see near the right hand side tail of the histogram may actually have local details blown out already.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    I am quite late to the digital back's party, and so this might not be a news to you guys.
    You're right, it isn't news to me.

    Quote Originally Posted by voidshatter View Post
    I am quite shocked that the native base ISO is not at 50 for nomal mode, or 140 for long exposure mode.
    As can be seen above for the case of normal mode, for the same lens at the same aperture, 50 ISO and 80 seconds has less highlight details recoverability than 100 ISO and 40 seconds.
    This is normal for most CCD digital backs. Here's a tip: forget about ISO in the MFD-CCD regime. In most cases, it's just a flag to the post-processing software - as illustrated by the flat parts of the DxO ISO curves you posted. Instead, think about what you've actually done...in the first photo you've exposed the sensor to twice as much light as in the second photo. Why then are you surprised that the first photo blows the highlights a stop sooner?


    Quote Originally Posted by voidshatter View Post
    As can be seen above for the case of long exposure mode, for the same lens at the same aperture, 140 ISO and 20 seconds has less highlight details recoverability than 200 ISO and 14 seconds.
    Ditto. Same reason.


    Quote Originally Posted by voidshatter View Post
    For some reason, Phase One has chosen to not explicitly tell the truth that this Dalsa CCD is indeed working at 100 ISO voltage. If you work at 50 ISO, then the histogram and lightlight warning are NOT reliable! You end up risk blowing up your highlights without being aware of! (The same holds for 140 ISO in long exposure mode.)
    And if you work at 50 ISO, what is happening to the mid-tones and shadows just as you are blowing the highlights? Answer: you gain a stop at one end, lose it at the other, and alter signal to noise in between. That is CCD-based MFD in a nutshell. Phase One is not telling untruths.

    So, trust your meter, set your exposure and fire away at ISO 50 if you want the best signal to noise. Shorten your shutter speed if the highlights are clipping. Whether or not you bump it up to a higher ISO while shortening the shutter speed is pretty irrelevant. ISO is just a flag, remember. It only determines the default brightness of the jpeg conversion. But you can override that.

    Quote Originally Posted by voidshatter View Post
    Further validating this, I have asked Bill Claff to run his algorithms on the IQ260 RAW files. (These test shots were taken at room temperature.) He got the following conclusions:
    I disagree with Bill's conclusion that "It's clear the base ISO is 100 since the ISO 50 result is the same." He doesn't seem to realise that raising ISO on these devices is just underexposing...and that underexposing is just shifting the same dynamic range up to a brighter range of intensities. Taking that to its logical conclusion, on a DB like mine with its completely flat ISO 'curve', one could theoretically set an ISO of anything you like between 50 and infinity, and pick the highest ISO setting which shows detail on the unfiltered Sun (if the shutter speed could go fast enough!) and call that the base ISO. So it just makes no sense to pick the higher value as base! The base ISO should be defined as the lowest ISO value which maintains the full dynamic range. Which in this case, is ISO 50.

    Ray
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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by ondebanks View Post
    So, trust your meter, set your exposure and fire away at ISO 50 if you want the best signal to noise. Shorten your shutter speed if the highlights are clipping. Whether or not you bump it up to a higher ISO while shortening the shutter speed is pretty irrelevant. ISO is just a flag, remember. It only determines the default brightness of the jpeg conversion. But you can override that.



    I disagree with Bill's conclusion that "It's clear the base ISO is 100 since the ISO 50 result is the same." He doesn't seem to realise that raising ISO on these devices is just underexposing...and that underexposing is just shifting the same dynamic range up to a brighter range of intensities. Taking that to its logical conclusion, on a DB like mine with its completely flat ISO 'curve', one could theoretically set an ISO of anything you like between 50 and infinity, and pick the highest ISO setting which shows detail on the unfiltered Sun (if the shutter speed could go fast enough!) and call that the base ISO. So it just makes no sense to pick the higher value as base! The base ISO should be defined as the lowest ISO value which maintains the full dynamic range. Which in this case, is ISO 50.

    Ray
    I always do ETTR myself by watching the histogram closely. I have proof that by using 50 ISO the histogram is then less reliable:





    As you can see, 50 ISO and 80 seconds give the same highlight warning as 100 ISO and 40 seconds (while in the OP it has been shown that the 50 ISO and 80 seconds setting has lost more highlight details). The highlight warning is based on what is shown on the screen (i.e. luminance level above a certain threshold, say, 240 or so). For the 50 ISO case, each pixel has been "post-processed" to pull down the exposure in the camera by one-stop, which is a behaviour of deceiving oneself!

    In this situation I would never trust the playback histogram of 50 ISO, because it is risky of blowing out highlight details without knowing. I would regard the trusty 100 ISO as the native base ISO.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    Moving from 50 to 100 ISO should create more noise in the shadow only if you shorten the exposure time (and as a result of faster shutter speed, you gain more detail recoverability in the highlight, so the total DR remains the same.). If you use the same shutter speed (and aperture) for both 50 ISO and 100 ISO you should then be able to recover the same amount of highlight details while retaining the same amount of noise in the shadow. Actually these two are both working at 100 ISO voltage. The 50 ISO setting is just like the extended ISO settings in Canon and Nikon camera bodies, i.e. they shoot at 100 ISO then pull down 1-stop exposure in the camera. Thus, the histogram and highlight warnings at 50 ISO are not reliable, because what you see near the right hand side tail of the histogram may actually have local details blown out already.
    I can only comment from my actual use. ISO 50 is much cleaner than even ISO 100 especially in the shadows. Shutter speed being the same. However even at 50 even 1/2 second can make a huge difference in noise differences seen between 1sec and 1/2 sec.

    Onebanks gives a better explanation in technical terms. CCD is not like CMOS where you actually can increase gain via an increase in ISO. I still find that at times a push to 200 is fine in good light to reach 1/60th or even 1/125th rather than under exposing 50 by that much as you won't recover the details. No doubt the 250 will do a better job here.

    Paul

    Paul

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by Paul2660 View Post
    I can only comment from my actual use. ISO 50 is much cleaner than even ISO 100 especially in the shadows. Shutter speed being the same. However even at 50 even 1/2 second can make a huge difference in noise differences seen between 1sec and 1/2 sec.

    Onebanks gives a better explanation in technical terms. CCD is not like CMOS where you actually can increase gain via an increase in ISO. I still find that at times a push to 200 is fine in good light to reach 1/60th or even 1/125th rather than under exposing 50 by that much as you won't recover the details. No doubt the 250 will do a better job here.

    Paul

    Paul
    Hi Paul, thanks for your experience. Do you have proof that 50 ISO is cleaner than 100 ISO in the shadow? i.e. the same aperture and the same shutter speed, but for 50 ISO vs 100 ISO



    Here are my test shots. The left hand side is 50 ISO 1 second, with +4 stops pull in Capture One, while the right hand side is 100 ISO 1 second, with +3 stops pull in Capture One. Honestly I do not see a difference of noise level.
    Last edited by voidshatter; 3rd June 2014 at 17:29.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    Here are my test shots. The left hand side is 50 ISO 1 second, with +4 stops pull in Capture One, while the right hand side is 100 ISO 1 second, with +3 stops pull in Capture One. Honestly I do not see a difference of noise level.
    Why would two identical exposures give you different noise?
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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by Shashin View Post
    Why would two identical exposures give you different noise?
    Yes, they are two identical exposures, i.e. I am trying to prove that "50 ISO 1 second" and "100 ISO 1 second" are capturing the same information into the RAW file, and hence concluding that 50 ISO is indeed working at 100 ISO (then "post-processed" by the camera body to pull down 1-stop for playback and histogram).

    The only difference here is the playback histogram in the camera body (and the default preview jpg embedded). The 50 ISO image looks darker in playback and first open in software, but it actually is an exposure at 100 ISO. The 50 ISO one would make you feel safer about the highlight but actually you risk blowing out the highlights without knowing from the playback in camera.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    Yes, they are two identical exposures, i.e. I am trying to prove that "50 ISO 1 second" and "100 ISO 1 second" are capturing the same information into the RAW file, and hence concluding that 50 ISO is indeed working at 100 ISO (then "post-processed" by the camera body to pull down 1-stop for playback and histogram).

    The only difference here is the playback histogram in the camera body (and the default preview jpg embedded). The 50 ISO image looks darker in playback and first open in software, but it actually is an exposure at 100 ISO. The 50 ISO one would make you feel safer about the highlight but actually you risk blowing out the highlights without knowing from the playback in camera.
    Well, if you give two identical exposures (by underexposing the ISO 50 by one stop), it is not surprising they would be identical. But I don't think you have proved anything except an underexposed ISO 50 exposure is similar to a correctly exposed ISO 100 exposure. Have you tried exposing based on the ISO and then comparing? That would let you know if they are different.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by Shashin View Post
    Well, if you give two identical exposures (by underexposing the ISO 50 by one stop), it is not surprising they would be identical. But I don't think you have proved anything except an underexposed ISO 50 exposure is similar to a correctly exposed ISO 100 exposure. Have you tried exposing based on the ISO and then comparing? That would let you know if they are different.
    I honestly don't quite follow you. I basically have two kinds of tests:

    a) "50 ISO 80 seconds" vs "100 ISO 40 seconds" (as shown in the OP). The latter has more highlight details but more shadow noise;

    b) "50 ISO 1 second" vs "100 ISO 1 second" (as shown in #10 post of this thread). They have the same shadow noise and the same highlight details.

    These two tests together verify that 50 ISO shots are working at 100 ISO physically.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    So, from your results, the ISO 50 has better shadow noise characteristics. Isn't that what Paul is saying?

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by Shashin View Post
    So, from your results, the ISO 50 has better shadow noise characteristics. Isn't that what Paul is saying?
    I don't think so.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    I honestly don't quite follow you. I basically have two kinds of tests:

    a) "50 ISO 80 seconds" vs "100 ISO 40 seconds" (as shown in the OP). The latter has more highlight details but more shadow noise;

    b) "50 ISO 1 second" vs "100 ISO 1 second" (as shown in #10 post of this thread). They have the same shadow noise and the same highlight details.
    In both cases, that is the behaviour I would expect to see.

    Quote Originally Posted by voidshatter View Post
    These two tests together verify that 50 ISO shots are working at 100 ISO physically.
    - or that 100 ISO shots are working at 50 ISO physically. Again, on what basis are you assuming that the higher ISO is the base one?

    On cameras which "pull" from base ISO, there's a giveaway in the DxOmark graphs: the pulled ISO point falls above the nominal 1:1 line. Here are the Canon 5DII and 6D for example; see where ISO 50 falls above the line for both cameras, while every other ISO point tracks slightly below the line:



    Now, look again at your DxOmark graph above, for the IQ180. ISO 50 (and indeed ISO 35 - which DxO have erroneously plotted as ISO 25!) lies below the 1:1 line. So ISO 50 is not "pulled" from base. Base is ISO 35 for this particular back, just as Phase One say. The next few higher ISOs lie further and further below the nominal line, so they are pushed rather than pulled. This is normal, and sensible, for fixed-readnoise CCDs.

    Then something odd happens: from ISO 200 and up, the curve starts to rise, because for no good reason Phase One start to mathematically clip the highlights at still higher ISOs - they apply a software gain before writing the RAW file, but this is just cutting down dynamic range at the bright end without any of the noise reduction at the faint end that one tends to get with Canon-type CMOS cameras. Bad firmware design on the part of Phase One.

    Also, there may indeed be a glitch in the IQ back's histogram feedback. From your photos, it appears to be based on a forward extrapolation to the processed jpeg, rather than on the RAW file.

    Ray
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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    As someone who trained and worked for many years as a pro in the era of shooting E-6 Tranny film in all formats from 35mm to 5x7in, back when real-world dynamic range was about 5.3 stops and 1/3stop overexposure meant blown highlights, the "terrible" performance of my IQ180 has me happy as a pig in sh*t. The dynamic range is huge, the results consistent and the final files I supply my clients FAR surpass the quality of anything I ever shot on tranny, even in the years when I was lucky enough to have a zillion-dollar Hell scanner in the room next to my office.
    I've spent time with people who spend heaps of their time testing and measuring and others who spend every available minute shooting, editing and printing. I know whose work product I'd rather be looking at.
    "In the end, it's all about the pictures"
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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by siebel View Post
    I've spent time with people who spend heaps of their time testing and measuring and others who spend every available minute shooting, editing and printing. I know whose work product I'd rather be looking at.
    "In the end, it's all about the pictures"
    I love looking at (and when all goes well, creating) beautiful photographs.

    I also love thoroughly understanding how the gear which creates them works.

    The two pleasures are not mutually exclusive.

    I never can understand why some people think they are.

    Ray
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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by siebel View Post
    I've spent time with people who spend heaps of their time testing and measuring and others who spend every available minute shooting, editing and printing. I know whose work product I'd rather be looking at.
    "In the end, it's all about the pictures"
    How did you determine that your E-6 chromes only have 5.3 stops of DR?

    Ansel Adams spent a great deal of time understanding his process. Henri Cartier Bresson did not. Technical knowledge is not the determining factor for talent. However, I challenge you to name one photographer that cannot control his process that is exceptional. Whether you intellectually or instinctively learn the craft of photography, you are not going to go very far if you are not skilled and that comes with knowledge. People come to the knowledge in different ways. And some of us in our work are required to have technical knowledge--do you believe that only your type of experience and knowledge should be shared?

    You are right. In the end, it is about the results. How a photographer gets there is neither here nor there. I don't think trying to divide photographers who are interested in the photographic process from those that are not into worthy and unworthy camps is useful. What I find ironic is photographers coming into technical discussions to simply announce they are above it all, especially when beginning a post with some kind of technical statement.
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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    I don't think so.
    Like Ray, I am just having a hard time with your conclusions. It get more confusing when you say you use ETTR as you are just ignoring ISO anyway. It seems the basis of your conclusion is that you prefer the in-camera histogram when the camera is set to ISO 100.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by ondebanks View Post
    On cameras which "pull" from base ISO, there's a giveaway in the DxOmark graphs: the pulled ISO point falls above the nominal 1:1 line. Here are the Canon 5DII and 6D for example; see where ISO 50 falls above the line for both cameras, while every other ISO point tracks slightly below the line:
    What I am trying to say is that the lowest point lying on the 1:1 line is regarded as the base native ISO, because when you further raise ISO beyond that with the same aperture and shutter speed, you start clipping more highlights.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    What I am trying to say is that the lowest point lying on the 1:1 line is regarded as the base native ISO, because when you further raise ISO beyond that with the same aperture and shutter speed, you start clipping more highlights.
    But don't you clip fewer highlights at ISO 200? Why isn't that the base ISO?

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by Shashin View Post
    Like Ray, I am just having a hard time with your conclusions. It get more confusing when you say you use ETTR as you are just ignoring ISO anyway. It seems the basis of your conclusion is that you prefer the in-camera histogram when the camera is set to ISO 100.
    Yes exactly. I prefer the in-camera histogram at ISO 100 to do my ETTR (which is the native base ISO). If I use the in-camera histogram at ISO 50 to do my ETTR (which is the extended ISO), I then risk blowing out highlight details. For the same aperture:

    a) "50 ISO 2 seconds" vs "100 ISO 1 second": the former should have less shadow noise but the latter should have more highlight details. The total DR remains the same;

    b) "50 ISO 2 seconds" vs "100 ISO 2 seconds": these should have the same shadow noise and the same highlight details. The total DR remains the same;

    c) "100 ISO 2 seconds" vs "200 ISO 1 second": the former should have less shadow noise but they both have the same highlight details. The total DR of the latter is less;

    d) "100 ISO 2 seconds" vs "200 ISO 2 seconds": the latter physically overexposes by 1 stop, and when pulled down in pp, the latter has 1-stop less highlight details. The total DR of the latter is less;

    e) "200 ISO 2 seconds" vs "400 ISO 1 second": the former should have less shadow noise but they both have the same highlight details. The total DR of the latter is less;

    f) "200 ISO 2 seconds" vs "400 ISO 2 seconds": the latter physically overexposes by 1 stop, and when pulled down in pp, the latter has 1-stop less highlight details. The total DR of the latter is less;

    ...

    You can see that ISO 100 is the turning point so ISO 100 is called the native base ISO.
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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by Shashin View Post
    But don't you clip fewer highlights at ISO 200? Why isn't that the base ISO?
    Because ISO 200 has less total DR than ISO 100 does, while ISO 100 has the same total DR as ISO 50. Check my explanation above.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Voidshatter:

    I have taken a few shots this morning, will not be able to get to them until this afternoon.

    ISO 50 and 100, are very close, and definitively much closer than 50 and 200. I want to shoot this a bit more, but so far, I feel that I still see the following:

    1. At iso 50, a bit cleaner shadows, however remember I am using a tech camera, and I have no 1/3 or 1/2 shutter gaps (this make a huge difference IMO). I still feel that 50 gives me more room in highlights, i.e when I expose to the right for the shadows. So, for example on a recent shoot, where I was working with both a ND 0.9 and CLPL at F11, I pushed (I call it that) to the right as much as .75 a stop. On the screen, camera LCD, the water was totally white showing blown out 255 255 255, however in C1, (I was tethered), I was able to get that high light back and still had water detail. OK, now that was at 1 second. I then went to 1.5 and 2 seconds (remember I am using a copol so hitting these speeds is totally hit and miss as I am in blub). But at 1.5 I could not recover my water, it was totally gone, so just .5 of a sec took it out of range.

    I tend to skip over 100 and jump to 200, so I don't have much experience there, but I will look at the stuff I took this morning and see.

    2. It's anyone's guess as to what the 260 is doing in Long Exposure Mode. I personally have not taken anything longer than 15 seconds and that at iso 50. I have however use 200 in LEM (long exposure Mode) and I don't see any difference in normal exposures. I had hoped that this would NOT be the case and that somehow Phase One could pull some more magic out of the newer chip. The 160 chip is the same as the P65 thus older and pretty much at end of life. So far I have not seen this and really 200 and 400 in LEM mode look pretty much the same as 200 and 400 in normal mode, in that both are pretty much worthless (sorry but it's true) in darker shadow areas. The details just are not there vs the noise. I have not worked much with LEM 140 either as it's just not much more than 100 in normal mode for standard (non long exposures).

    3. In the Library tests that Doug did, I was personally shocked by the 6 second shots that were taken by the 260. There were thousands of stuck pixels and by my thinking, the 260 with a mandatory dark frame should have removed this. With my 260 at exposures up to 15 seconds in low light I have been so far pleased with the results at iso 50.

    4. You may be right, in that the iso 50 setting is "fake" and the back is really working at 100. I just can't tell enough from my work, as I always use 50 unless pushed to 200 by conditions, (wind/motion). Only Phase knows this and they don't tend to join this forum or others and only they really know. My rule of thumb, is if I have good light then take the 260, (even with windy conditions) as I can use 200 when needed. In theory 1/60th at 200 should be the same as 1/50th at iso 50, since CCD's really only work at base iso from what I understand. However over and over I see better results at 200 (expect in shadows), so leaves sky etc will be better off. I am a photographer who tends to shift everything to create a pano later on, albeit a short pan, so my shifts to 15mm will suffer the worse with noise.

    This whole issue of "what iso is a CCD back really using" is one of those things that you just can't find enough info about. I think that Phase One wants the photographer to think that the CCD backs work the same as a CMOS chip, so the iso is a true increase in gain, but it's not. From what I understand, it only a marker to the raw file.

    So for me I guess every shoot is an experiment as it's just hard to tell what combination will work. Again, the ability to be tethered to a S Pro 2 and look at the actual raw helps a lot as you can judge much more "true" info about the image in relation to highlights, shadows noise.

    I understand your concern, so really the best idea is shoot both backs if you can, and then make the call from that. Long term, by far the 250 is the better investment. I saw this type of recovery 2.5 years ago with the D800 and overnight I switched 14 years of Canon equipment to Nikon, I have never looked back, the differences at base iso are just that much better. CCD backs by the nature of the CCD chip, just won't get there thus you have to shoot around that issue.

    Much more info than you want I am sure, I end it with this, when I get it right with the 260, it looks great and I love the output, which is why I always lead with that back.

    Paul

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    What I am trying to say is that the lowest point lying on the 1:1 line is regarded as the base native ISO,
    But none of the IQ180 points lie on the 1:1 line. They all lie under it. And the one which lies closest to the line is the ISO 35 one. That's why it is base ISO. It comes closest to meeting the nominal ISO standard, while also maintaining the maximum available DR.

    Quote Originally Posted by voidshatter View Post
    because when you further raise ISO beyond that with the same aperture and shutter speed, you start clipping more highlights.
    You don't start clipping more highlights...not in this back's RAW files at ISO 50 or 100. Not in most other CCD-MFD backs' RAW files, at all. Not even in your own tests! I already gave the reasons above. The DR window slides around...it doesn't start to close down. You are applying thinking from a different camera design paradigm, the one where increasing gain is applied either in hardware or firmware as ISO is increased, and the ISO curve tracks the slope of the 1:1 line. That does happen eventually in the IQ180 from ISO 200 and up, but not at ISO 50 and 100.

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by ondebanks View Post
    But none of the IQ180 points lie on the 1:1 line. They all lie under it. And the one which lies closest to the line is the ISO 35 one. That's why it is base ISO. It comes closest to meeting the nominal ISO standard, while also maintaining the maximum available DR.



    You don't start clipping more highlights...not in this back's RAW files at ISO 50 or 100. Not in most other CCD-MFD backs' RAW files, at all. Not even in your own tests! I already gave the reasons above. The DR window slides around...it doesn't start to close down. You are applying thinking from a different camera design paradigm, the one where increasing gain is applied either in hardware or firmware as ISO is increased, and the ISO curve tracks the slope of the 1:1 line. That does happen eventually in the IQ180 from ISO 200 and up, but not at ISO 50 and 100.

    Ray
    Check #24 post of this thread

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    A CCD based sensor is really ISOless (supposedly so is the nikon d800, although I haven’t tested that yet, so ISO is basically a metadata setting.

    One issue is the actual base ISO of each sensor (or perhaps each sensor batch) varies. So when the backs are made some type of average is used. i’ve heard the sensors in the 180 series can actually be as low as 25 and as high as 50, so 35 was the established base.

    Perhaps what you are finding is the actual base ISO of your particular sensor if measured would end up more in the 80 range so a little on the high side as compared to other 160 sensors?

    personally thats’ one thing I don’t like about the 180 ... the ISO 35 puts me at too long of exposure times or forces me to underexpose. I wish it was 100, I can always use neutral density when I want to drag the shutter.
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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    Check #24 post of this thread
    I'm not sure which part of your post you are referring to, but I guess it is this? - "You can see that ISO 100 is the turning point so ISO 100 is called the native base ISO."

    Ok, let's look at some other MFD backs. Here are two from Hasselblad. By your argument above, you would conclude that these backs have no turning points so they have no native base ISO (!!), while I would conclude that the base ISO is clearly ISO 50 for both. Hasselblad users, which would you agree with?



    Meanwhile, to further show just how malleable (arbitrary, meaningless, fake - take your pick) the above-base-ISO settings are in MFD CCD systems, let's compare two Phase One ISO curves, P45+ and P40+. These are both CCDs, 39MP and 40MP respectively, and both are from the "P+" generation of Phase One backs:





    It's kind of funny how in one back, Phase One decided to initially track the nominal curve, then had a change of heart and went flat. In the other, they did the exact opposite - initially flat, then sloping!

    Oh, and BTW, the P45+ uses the exact same KAF-39000 sensor as the H3DII-39 in the plot above. Same sensor, different ISO curve above ISO 50 - by your definition, they have different turning points (one has none at all!) so they have different base ISOs - but how can that be, as this is the same sensor??

    The answer is that firstly, base ISO is 50 for both, and secondly, the back manufacturers can do whatever they please above that base ISO, knowing that it won't make any difference - it's all just underexposure with crappier and crappier shadow detail. The smarter ones (like Hasselblad here) leave ISO as a pure flag, and in this way they at least maintain full (but shifted) DR through the complete ISO range.

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by ondebanks View Post
    I'm not sure which part of your post you are referring to, but I guess it is this? - "You can see that ISO 100 is the turning point so ISO 100 is called the native base ISO."

    Ok, let's look at some other MFD backs. Here are two from Hasselblad. By your argument above, you would conclude that these backs have no turning points so they have no native base ISO (!!), while I would conclude that the base ISO is clearly ISO 50 for both. Hasselblad users, which would you agree with?



    Meanwhile, to further show just how malleable (arbitrary, meaningless, fake - take your pick) the above-base-ISO settings are in MFD CCD systems, let's compare two Phase One ISO curves, P45+ and P40+. These are both CCDs, 39MP and 40MP respectively, and both are from the "P+" generation of Phase One backs:





    It's kind of funny how in one back, Phase One decided to initially track the nominal curve, then had a change of heart and went flat. In the other, they did the exact opposite - initially flat, then sloping!

    Oh, and BTW, the P45+ uses the exact same KAF-39000 sensor as the H3DII-39 in the plot above. Same sensor, different ISO curve above ISO 50 - by your definition, they have different turning points (one has none at all!) so they have different base ISOs - but how can that be, as this is the same sensor??

    The answer is that firstly, base ISO is 50 for both, and secondly, the back manufacturers can do whatever they please above that base ISO, knowing that it won't make any difference - it's all just underexposure with crappier and crappier shadow detail. The smarter ones (like Hasselblad here) leave ISO as a pure flag, and in this way they at least maintain full (but shifted) DR through the complete ISO range.

    Ray
    This is easy to judge

    For the H3D case the base native ISO can be called anything since throughout the whole range you do not clip more highlights and in this case the ISO is just a metadata;

    For the P45+ case the base native ISO is 50 (since you start to clip highlights beyond 50);

    For the P40+ case the base native ISO is 100 (since you start to clip highlights beyond 100).

    The point here is to find out when you start to blow out highlight as you raise the ISO while you stay with the same aperture and shutter speed, so you know that you get the perfect shot with ETTR. Yes, of course if you are familiar with, say, the IQ260 digital back working at 50 ISO and know that you can pull back something like 1.5 stops of highlight beyond the default luminance level 240 stuff in the in-camera histogram warning (just the same as 2.5 stops beyond 100 ISO mode) then okey it's totallly fine.

    If you still cannot quite follow what I am talking about, then open dxomark, click on the "Dynamic Range" tab in Measurements for a digital back. If you hover your mouse over the left-most data point and read the "Manufacturer ISO", then that is the base native ISO for the digital back.
    Last edited by voidshatter; 4th June 2014 at 17:18.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Hi Ray

    I think I get it

    To put it in laymen's terms - (or dumber)

    To get the best image - best practice (ideal) would be shoot on a tripod at base iso., adjust shutter speed to your exposure requirement - not mentioning aperture as mentally that is preset. -- This is what I do now on the Phase 80 set at 35 or 50 iso.

    After that, when hand holding and options are limited by light - changing iso is in effect underexposing and telling C1 to stretch the captured information -- to put "pixels" in different zones? Stretch the pixels to fulfill the DR?

    So if you need a certain shutter / aperture moving up the iso does NOT change the amount of information captured - only redistributes it?

    OTOH - Stay at "base iso and adjusting the shutter / aperture - will in effect - give more or less information in your file to work with. We all see how much smaller an underexposed file is compared to a correct or overexposed file.

    Is Senor Plus any different? I have found that at iso 400 on the 280 - the file is better (less noise and just smoother) in Sensor plus (20 meg) as opposed to full resolution. Is this my imagination?

    Thanks

    Phil
    Last edited by alajuela; 4th June 2014 at 17:35.
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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    This is easy to judge

    For the H3D case the base native ISO can be called anything since throughout the whole range you do not clip more highlights and in this case the ISO is just a metadata;

    For the P45+ case the base native ISO is also 50 (since you start to clip highlights beyond 50);

    For the P40+ case the base native ISO is 100 (since you start to clip highlights beyond 100).

    The point here is to find out when you start to blow out highlight as you raise the ISO, so you know that you get the perfect shot with ETTR.
    Then you are adopting a definition of base native ISO that I don't think anyone else uses. To say that the base ISO of the old Hasselblad backs could be ISO 400...I mean, really?! Sure, ETTR would not clip highlights at their ISO 400, but if you ETTR with such a back you are doing one of two things - depending on whether the histogram shows the RAW data or the ISO-flag-scaled data:

    - If the histogram shows the RAW data, by using ETTR you are not actually shooting at ISO 400 - you are bypassing the ISO stuff altogether and filling the pixels to just under saturation - which requires the same exposure (shutter and aperture) as at the lowest ISO setting of 50. You will get the same ETTR results shooting ISO 50 without exposure compensation as shooting ISO 400 and forcing +3 stops exposure compensation. Isn't it more natural to define base native ISO as the ISO which allows you to ETTR by normal metering, without the need for exposure compensation?

    - If OTOH the histogram shows the ISO-flag-scaled data, you are truly shooting at ISO 400, so by using ETTR you are using 3 stops less exposure than at ISO 50...[why else would you pick ISO 400, if not to tell the meter/AE system to underexpose and use a faster shutter speed?]. But then there would be a severe impact on image quality from underexposing everything in the scene by 3 stops. Which is why ISO 400 certainly could not be considered base ISO. Base ISO implies maximum usage of the pixel well depth, for high signal to noise.

    And shouldn't the definition of something as fundamental as "native base ISO" also include an expectation of adhering to the ISO standard, marked by the nominal 1:1 line? "ISO 400" on the Hasselblads is huge distance from the line - it's measured as ISO 46, so it's just over 3 stops from its declared value. Whereas "ISO 50" is the same measured ISO 46, so it's only a fraction of a stop off.

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    If you still cannot quite follow what I am talking about, then open dxomark, click on the "Dynamic Range" tab in Measurements for a digital back. If you hover your mouse over the left-most data point and read the "Manufacturer ISO", then that is the base native ISO for the digital back.
    Unfortunately that doesn't really help to pin down base native ISO, as hovering over any of the other points also shows a different value for the "Manufacturer ISO".

    But are you really admitting that the left-most data point for DBs is always the base native ISO? That has been my contention all along!

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by ondebanks View Post
    Unfortunately that doesn't really help to pin down base native ISO, as hovering over any of the other points also shows a different value for the "Manufacturer ISO".

    But are you really admitting that the left-most data point for DBs is always the base native ISO? That has been my contention all along!

    Ray
    I guess you still don't quite get it. You are confusing the left-most data point for the "ISO Sensitivity" tab with the "Dynamic Range" tab.

    The base native ISO should be the ISO that gives you the best dynamic range result in the "Dynamic Range" tab. If there are multiple values giving you the same (top) dynamic range performance, then the highest ISO is the native base ISO.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Is there such a thing as "native base ISO"? I have seen the ISO standard; they have no such thing. They do have a saturation-based ISO, but you are not using a method to determine that. They also have a S/N ratio based ISO, but you are not using that either.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    I guess you still don't quite get it. You are confusing the left-most data point for the "ISO Sensitivity" tab with the "Dynamic Range" tab.
    Nope. I had checked it in the "Dynamic Range" tab.

    BTW, DxO screw up when they plot Dynamic Range for ISO-flag backs like the aforementioned Hasselblads. Rather than measuring it at ISOs above 50, they plot "extrapolated" values which show a steady DR decline of 1 eV/stop. If they took the time to actually measure it in the RAW file rather than extrapolating to what they think the processing software would do, they'd find that DR doesn't decline and is constant across the ISO range.

    Quote Originally Posted by voidshatter View Post
    The base native ISO should be the ISO that gives you the best dynamic range result in the "Dynamic Range" tab. If there are multiple values giving you the same (top) dynamic range performance, then the highest ISO is the native base ISO.
    And we come full circle. Why the highest? You have not yet given a reason that stands up. In CMOS cameras, we might pick the highest because their readnoise often decreases with increased ISO. In MFD CCDs, there's no such improvement. If you're relying on an ETTR approach, then in my last post I explained why choosing the higher ISO is either pointless, or damaging to image quality. I wish you'd address those points.

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by Shashin View Post
    Is there such a thing as "native base ISO"? I have seen the ISO standard; they have no such thing. They do have a saturation-based ISO, but you are not using a method to determine that. They also have a S/N ratio based ISO, but you are not using that either.

    Film speed - Wikipedia, the free encyclopedia
    Will, it's a somewhat fuzzy concept alright - a spin-off from the saturation-based ISO you mentioned.

    In our MFD CCDs it's very simple though - there's only one real ISO and it's the saturation-based one (or a value close to it, with more headroom) that the manufacturers arrive at. This is always the smallest ISO value offered with the MFD setup and can be termed base ISO, since it's the optimum setting to shoot at, conditions permitting. As shooting at any higher ISO setting means capturing less light, then the *original* max signal part of the scene now drops 1 or more stops below the saturation level, and since readnoise doesn't change with ISO, signal to noise falls right across the scene. DR however stays constant, since something even brighter and previously saturated can now drop into the sub-saturation counts regime. (Although there's no requirement that there be something brighter to avail of this space - the DR definition [Saturation Level/Readnoise] is blind to what's being captured). If I raise ISO, saturation level aka Full Well Capacity ain't changing and neither is Readnoise. So DR stays constant.

    With the CMOS cameras, it's more complicated because a change in ISO can change both saturation level and readnoise, and as a consequence, DR and signal to noise would both change too. In that melee, if the very lowest ISO offered causes overexposure according to the saturation-based ISO, and if its readnoise is worse than the next ISO up, then for reasons of either DR, signal to noise, or both, the next ISO up is a better candidate for base or native ISO. It seems to me that voidshatter has zoned in on that fact and is applying it inappropriately to CCD MFD.

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by ondebanks View Post
    Nope. I had checked it in the "Dynamic Range" tab.

    BTW, DxO screw up when they plot Dynamic Range for ISO-flag backs like the aforementioned Hasselblads. Rather than measuring it at ISOs above 50, they plot "extrapolated" values which show a steady DR decline of 1 eV/stop. If they took the time to actually measure it in the RAW file rather than extrapolating to what they think the processing software would do, they'd find that DR doesn't decline and is constant across the ISO range.



    And we come full circle. Why the highest? You have not yet given a reason that stands up. In CMOS cameras, we might pick the highest because their readnoise often decreases with increased ISO. In MFD CCDs, there's no such improvement. If you're relying on an ETTR approach, then in my last post I explained why choosing the higher ISO is either pointless, or damaging to image quality. I wish you'd address those points.

    Ray
    There is a reason why dxomark ignore the lower values (non native ISO) when plotting the "Dynamic Range" tab. If you look into comcast's plot, you find things like the following:



    Anything below 100 ISO on a D800E does not give you more DR range.

    Unless you have definitive analysis of dynamic range in terms of highlight details and SNR in shadow to prove that anything below 100 ISO on a D800E or IQ260 could give you better total DR range, I would rather trust comcast or dxomark instead.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    There is a reason why dxomark ignore the lower values (non native ISO) when plotting the "Dynamic Range" tab. If you look into comcast's plot, you find things like the following:


    Anything below 100 ISO on a D800E does not give you more DR range.

    Unless you have definitive analysis of dynamic range in terms of highlight details and SNR in shadow to prove that anything below 100 ISO on a D800E or IQ260 could give you better total DR range, I would rather trust comcast or dxomark instead.
    ?? I have never said that you get better DR below ISO 100 on an IQ260. I said that you get constant DR at ISO 35, 50 and 100 on an IQ180. But you get the best SNR at ISO 35, somewhat less at ISO 50 and even less SNR at ISO 100. So the optimum (base) ISO is 35. Do you dispute any of this? Does comcast?

    And I have never referred to the D800E at all - it's irrelevant to this exchange, as it is not using a CCD!

    You started this thread with a question about the IQ260. I have answered it as helpfully as I could, based on an intimate knowledge of how CCDs work (I lecture in observational astronomy) and on my own experience as a MFD user. Now seeing as DxO have never tested that back, nor comcast - I don't see a single MFD device listed at comcast -, how can you say that you would trust them over my analysis?

    Ray
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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by ondebanks View Post
    ?? I have never said that you get better DR below ISO 100 on an IQ260. I said that you get constant DR at ISO 35, 50 and 100 on an IQ180. But you get the best SNR at ISO 35, somewhat less at ISO 50 and even less SNR at ISO 100. So the optimum (base) ISO is 35. Do you dispute any of this? Does comcast?

    And I have never referred to the D800E at all - it's irrelevant to this exchange, as it is not using a CCD!

    You started this thread with a question about the IQ260. I have answered it as helpfully as I could, based on an intimate knowledge of how CCDs work (I lecture in observational astronomy) and on my own experience as a MFD user. Now seeing as DxO have never tested that back, nor comcast - I don't see a single MFD device listed at comcast -, how can you say that you would trust them over my analysis?

    Ray
    Total DR range is related to the highlight details and the SNR in the shadow. When you claim that you get cleaner results at 35 or 50 ISO, you also claim to have more total DR range.

    The data I posted in the OP was the analysis results by comcast (the site owner sent me these by email but haven't updated his site yet).

    Can you prove that for the same highlight details, you can get better shadow SNR at 50 ISO, vs 100 ISO? (I believe for the same amount of highlight details, when comparing the SNR in the shadow, 100 ISO is cleaner than 200 ISO, but 50 ISO is not cleaner than 100 ISO.)

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    Total DR range is related to the highlight details and the SNR in the shadow. When you claim that you get cleaner results at 35 or 50 ISO, you also claim to have more total DR range.
    No - in my last couple of posts, I explained that you can raise or lower SNR on the scene of interest while simultaneously maintaining constant DR. What I think you're not perceiving is that the DR is not tied to the objects within the scene. Particular highlights and particular shadow details slide in and out of the DR window, and up and down in SNR, depending on how much exposure we give the sensor. The DR window itself never changes size as long as it's in the flagged-ISO regime. It's always going to be equal to unchanging saturation value divided by unchanging readnoise value.


    Quote Originally Posted by voidshatter View Post
    The data I posted in the OP was the analysis results by comcast (the site owner sent me these by email but haven't updated his site yet).
    Fair enough. But what you posted from Bill (and I'm a great admirer of his work) is only a DR number for each ISO. He does confirm the equal DR at ISO 50 and 100 (and ISO 35 would be the same, if you'd shot that as well). But he doesn't provide a SNR value for anything specific within the photo - say, the classic photographer's grey card - at ISO 35, ISO 50, ISO 100 and so on. If he had, that SNR would decline as ISO rises because, obviously, every ISO stop increase is another halving of exposure received. So equal DR is indeed simultaneous with cleaner SNR at lower ISO.


    Quote Originally Posted by voidshatter View Post
    Can you prove that for the same highlight details, you can get better shadow SNR at 50 ISO, vs 100 ISO?
    I think this statement is a breakthrough helping to understand where each of us is coming from. Your use of the phrase "the same highlight details" is key. I don't talk about the same highlight details - I just talk about highlights. As I said, DR is not tied to particular scene details. If we change from ISO 100 to ISO 50, meaning a doubling of exposure, I know that one stop of highlight details slides out the top of the DR window (saturates) and one stop of new fainter shadow details slides in at the bottom end. Everything in between moves up in SNR. But there's no free lunch in this regime - you cannot improve shadow detail or overall SNR without blowing those top highlights.

    Does this resolve our debate? I hope so.

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by ondebanks View Post
    No - in my last couple of posts, I explained that you can raise or lower SNR on the scene of interest while simultaneously maintaining constant DR. What I think you're not perceiving is that the DR is not tied to the objects within the scene. Particular highlights and particular shadow details slide in and out of the DR window, and up and down in SNR, depending on how much exposure we give the sensor. The DR window itself never changes size as long as it's in the flagged-ISO regime. It's always going to be equal to unchanging saturation value divided by unchanging readnoise value.




    Fair enough. But what you posted from Bill (and I'm a great admirer of his work) is only a DR number for each ISO. He does confirm the equal DR at ISO 50 and 100 (and ISO 35 would be the same, if you'd shot that as well). But he doesn't provide a SNR value for anything specific within the photo - say, the classic photographer's grey card - at ISO 35, ISO 50, ISO 100 and so on. If he had, that SNR would decline as ISO rises because, obviously, every ISO stop increase is another halving of exposure received. So equal DR is indeed simultaneous with cleaner SNR at lower ISO.




    I think this statement is a breakthrough helping to understand where each of us is coming from. Your use of the phrase "the same highlight details" is key. I don't talk about the same highlight details - I just talk about highlights. As I said, DR is not tied to particular scene details. If we change from ISO 100 to ISO 50, meaning a doubling of exposure, I know that one stop of highlight details slides out the top of the DR window (saturates) and one stop of new fainter shadow details slides in at the bottom end. Everything in between moves up in SNR. But there's no free lunch in this regime - you cannot improve shadow detail or overall SNR without blowing those top highlights.

    Does this resolve our debate? I hope so.

    Ray
    We are talking in circles...

    To make it simple:

    For the same aperture and shutter speed on the IQ260:

    a) 50 ISO vs 100 ISO: you have the same highlight details and shadow SNR, because these two exposures are physically the same, and the same information has been stored in the RAW file;

    b) 100 ISO vs 200 ISO: you have less highlight details (and less total DR range) for the latter;

    c) 200 ISO vs 400 ISO: you have less highlight details (and less total DR range) for the latter;

    d) 400 ISO vs 800 ISO: you have less highlight details (and less total DR range) for the latter...

    Do you see the difference here? 100 ISO is the turning point.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    We are talking in circles...

    To make it simple:

    For the same aperture and shutter speed on the IQ260:

    a) 50 ISO vs 100 ISO: you have the same highlight details and shadow SNR, because these two exposures are physically the same, and the same information has been stored in the RAW file;

    b) 100 ISO vs 200 ISO: you have less highlight details (and less total DR range) for the latter;

    c) 200 ISO vs 400 ISO: you have less highlight details (and less total DR range) for the latter;

    d) 400 ISO vs 800 ISO: you have less highlight details (and less total DR range) for the latter...

    Do you see the difference here? 100 ISO is the turning point.
    Yes, I see that 100 ISO is the turning point.

    But don't you see that 100 ISO is lower in SNR than ISO 35 and ISO 50?

    So if your focus is purely DR, ISO 100 is an equally good setting as ISO 35 and 50. You can treat it as some sort of special turning point if you wish.

    Typical photographers, OTOH, will want to maximise SNR as well as DR. So they will realise that this ISO 100 turning point is irrelevant and use a lower ISO.

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Oh! I just caught this:

    Quote Originally Posted by voidshatter View Post
    We are talking in circles...

    For the same aperture and shutter speed on the IQ260:
    Why would you use the same aperture and shutter speed at a higher ISO? In MFD CCDs, the only reason you raise ISO is in order to get your light meter/AE system to reduce exposure.

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by ondebanks View Post
    Yes, I see that 100 ISO is the turning point.

    But don't you see that 100 ISO is lower in SNR than ISO 35 and ISO 50?

    So if your focus is purely DR, ISO 100 is an equally good setting as ISO 35 and 50. You can treat it as some sort of special turning point if you wish.

    Typical photographers, OTOH, will want to maximise SNR as well as DR. So they will realise that this ISO 100 turning point is irrelevant and use a lower ISO.

    Ray
    As I have already stated (many times), the in-camera histogram and highlight warning acts the same for 100 ISO and above to the same degree of highlight recoverability, but less conservative/cautious for 50 ISO.

    When you check the in-camera histogram and highlight warning, for 100 ISO and greater ISOs you have something like 2.5 stops of highlight recoverability for the warning areas, but for 50 ISO you only have something like 1.5 stops of highlight recoverability. 50 ISO is simply standing alone here.

    Light meter is reliable but you can only do matrix metering (or use Pocket Light Meter app in iPhone to do spot metering). You would always have to check the in-camera histogram to make sure you have done ETTR (to optimize shadow SNR) without blowing out the important areas where you want to keep highlight details. This is a practice and learn process, and it is important to get familiar with how much room you have for the in-camera warning areas. If you prefer 50 ISO (1.5 stops highlight recoverability) that's totally fine, but I would prefer 100 ISO (2.5 stops highlight recoverability) because it is consistent with higher ISO values. That's why I call 100 ISO the base native.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by ondebanks View Post
    Oh! I just caught this:



    Why would you use the same aperture and shutter speed at a higher ISO? In MFD CCDs, the only reason you raise ISO is in order to get your light meter/AE system to reduce exposure.

    Ray
    Why would I not? For 50 ISO vs 100 ISO, the same aperture and the same shutter speed simply gives you the same RAW file (same shadow SNR, same highlight details, same total DR range). For 200 ISO and above, then if you keep the same aperture and shutter speed, you start losing highlight details and total DR range; even if you shorten your exposure time for higher ISOs, you still lose total DR range.

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    Why would I not?
    Because for one thing, your default RAW conversions will come out too bright, once the ISO flag kicks in. That's not too bad (you can override it), but I would worry that it might also make your in-camera histograms too bright.

    For another, it's just strange to pretend you're shooting at higher ISO, when all you've done is taken the correct exposure setting for ISO 35 and labelled it ISO 100. No law against it, but it does sort of distort the record. If someone were to try to replicate your "ISO 100" work with a different camera, they'd get badly blown results. Or they'd wonder whether their light meter, set to ISO 100, was faulty. Remember how far below the nominal ISO line that ISO 100 point lay, for the IQ180.

    Quote Originally Posted by voidshatter View Post
    For 50 ISO vs 100 ISO, the same aperture and the same shutter speed simply gives you the same RAW file (same shadow SNR, same highlight details, same total DR range). For 200 ISO and above, then if you keep the same aperture and shutter speed, you start losing highlight details and total DR range; even if you shorten your exposure time for higher ISOs, you still lose total DR range.
    Agree with all that.

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Quote Originally Posted by voidshatter View Post
    As I have already stated (many times), the in-camera histogram and highlight warning acts the same for 100 ISO and above to the same degree of highlight recoverability, but less conservative/cautious for 50 ISO.

    When you check the in-camera histogram and highlight warning, for 100 ISO and greater ISOs you have something like 2.5 stops of highlight recoverability for the warning areas, but for 50 ISO you only have something like 1.5 stops of highlight recoverability. 50 ISO is simply standing alone here.

    Light meter is reliable but you can only do matrix metering (or use Pocket Light Meter app in iPhone to do spot metering). You would always have to check the in-camera histogram to make sure you have done ETTR (to optimize shadow SNR) without blowing out the important areas where you want to keep highlight details. This is a practice and learn process, and it is important to get familiar with how much room you have for the in-camera warning areas. If you prefer 50 ISO (1.5 stops highlight recoverability) that's totally fine, but I would prefer 100 ISO (2.5 stops highlight recoverability) because it is consistent with higher ISO values. That's why I call 100 ISO the base native.
    OK, so you are forced to do it by that histogram glitch in the IQ260's firmware...but that doesn't make it a universal principle for MFD!

    Ray

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    Re: IQ260 native base ISO is at 100 for normal mode, and 200 for long exposure mode

    Maybe I overlooked this in the previous posts, but time has to be taken out of the equation. Running the sensor 2X longer at ISO 50 is going to increase noise. Instead of doubling the exposure time, keep time constant and adjust the lens aperture one time. Also, give the sensor time to cool down. 40 second exposures are going to warm up the sensor and increase noise levels.

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