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

?? 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.)
 

ondebanks

Member
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.


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.


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
 
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.
 

ondebanks

Member
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
 

ondebanks

Member
Oh! I just caught this:

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
 
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.
 
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.
 

ondebanks

Member
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.

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
 

ondebanks

Member
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
 

John Black

Active member
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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