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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.
 

gerald.d

Well-known member
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.
 

Shashin

Well-known member
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.
 

Paul2660

Well-known member
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
 
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.
 

ondebanks

Member
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.

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?


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.


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. :lecture: 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.

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
 
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.
 

Paul2660

Well-known member
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
 
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.
 
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Shashin

Well-known member
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?
 
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.
 

Shashin

Well-known member
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.
 
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.
 

Shashin

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

ondebanks

Member
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.

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
 

goesbang

Member
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"
 

ondebanks

Member
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. :confused:

Ray
 

Shashin

Well-known member
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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