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09-03-2018, 08:35 AM   #46
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QuoteOriginally posted by normhead Quote
Looking at the example images.... I don't really care. Shooting at base ISO is best practice. That is what I see in those images. I've been saying that for a long time before someone made up ISO invariance. Funny how someone takes a simple concept, and turns it into some thing complicated.

The explanation, base ISO uses more light to form the image. More light means less noise.. No need for a term like ISO invariance to explain it. I fail to see the advantage of getting all complicated.

ALlthe images are noisy, so the claim is that one bad image is better than another bad image. I'm not sure I care based on the examples provided. It would have been better if they were de-noised and then compared.
But sometimes your settings are such that at base ISO, the image is too dark. So the question then becomes, raise the ISO or lighten it in post? ISO invariance says there will be no difference.

09-03-2018, 01:11 PM   #47
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QuoteOriginally posted by normhead Quote
Funny how someone takes a simple concept, and turns it into some thing complicated.
Iso invariance is not a concept - it is a description of the performance of certain sensors.
Utilising Iso invariance is a concept - a subtle change in technique. Many Pentaxians are instinctly using it anyway.
It does not improve noise -it merely improves your control over the dynamic range.

The horse on the beach can serve as an example.
I presume it is at Iso 100. Lets say it would be good to have some more detail in the dark areas.
So we use the curves tool in pp to bring up the shadows two stops and hold the highlights back where they are now.

In a non Iso invariant camera the shadow area would be degraded.

In an Iso invariant camera the shadow area would effectively be at Iso 400 with the usual noise associated with 400 and the highlight area will have the tonal range and noise of the original 100 Iso

It is simple as that.
09-04-2018, 07:52 AM   #48
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QuoteOriginally posted by GUB Quote
Iso invariance is not a concept - it is a description of the performance of certain sensors.
Utilising Iso invariance is a concept - a subtle change in technique. Many Pentaxians are instinctly using it anyway.
It does not improve noise -it merely improves your control over the dynamic range.

The horse on the beach can serve as an example.
I presume it is at Iso 100. Lets say it would be good to have some more detail in the dark areas.
So we use the curves tool in pp to bring up the shadows two stops and hold the highlights back where they are now.

QuoteQuote:
In a non Iso invariant camera the shadow area would be degraded.
In an Iso invariant camera the shadow area would effectively be at Iso 400 with the usual noise associated with 400 and the highlight area will have the tonal range and noise of the original 100 Iso

It is simple as that.
QuoteQuote:
It does not improve noise -it merely improves your control over the dynamic range.
Example? I mean I know you say it does but, you present no evidence. Iignore ISO altogether. The base ISO of the sensor doesn't ever change, it's physical characteristic.bAll that matters to the sensor is how long the exposure is. What happens after that is all about boosting the signal in camera, or if you choose, boosting it in post processing software. Shooting with higher ISO shortens the exposure time. This invariably degrades the image, increases noise etc. Less signal increase the signal to noise ratio and the noise is increased as well as the signal.

You say it increases your control over dynamic range. It could. However there are great number of images where that's not true. The majority. Well over 50% of my images the camera's ability to capture the dynamic range at 200, 400 or even 3200 ISO is not exceeded. There is not improvement in dynamic range to be had. That makes this point irrelevant. In fact that's just part of knowing how to use your camera. There are a lot of times when a faster shutter speed is more important than the possibility of maximum IQ because if you don't use a fast shutter speed you get nothing. So your choice is clipped dynamic range or no worthwhile image at all. You speak of invariance as if you can just shoot base ISO. In you example of the horse, you shoot 100 ISO but your shutter speed is slow enough the horse moves slightly and you get a blurred image. You have nothing. The guy shooting at 3200 ISO has an image. Maybe he has restricted DR, maybe not.

What is ridiculous is that there is invariance. There isn't. Even the author of the quoted article says that. It's a concept which as far as I can tell in only applicable to images shot in less than Ideal lighting conditions. The only possible use would be in selecting a camera that is relatively ISO invariant, but no one tells you which cameos those are so even that is nonsense.

Shot at 1600 ISO


The highlights are blown and the shadows are black where I want them to be. There is virtually no noise. What would be the advantage of shooting this at 100 ISO? I'd have to set up a tripod. The dynamic range was very limited, low light, no dark shadows, probably an EV of 5 or less in the original scene.

You whole argument seems to be that you should shoot at base ISO and then increase your exposure values in post.
That depends entirely on the post processing editor being better than the in camera software.

So to make the case for invariance being a thing with considering, I'd have to see some examples of images I owl actually use, Whaat's posted in the thread displayed above is crap. I wouldn't use any of them, base ISO or 1600 ISO or 3200 ISO. If the noise is that bad, they all suck. As for dynamic range, the opinion seems to be you can't rescue highlights or shadows at higher ISOs.

Two comments there, one, the whole point of using a higher ISO is so you can properly expose your shadows and have an image come off the camera ready to use. So you are intentionally discarding some of the shadow detail if present, and usually it isn't even present.

My argument against the concept of invariance beyond that it doesn't actually exist, is that it doesn't really add anything to standard shooting practice. Perhaps only of interest to the inexperienced who don't have a lot of understanding of how cameras work.

My advice would be forget it. learn to ue your camera to best effect for what you are doing. If that means shooting everything at base ISO go ahead. Everyone should. However Everyone should also understand that given a base ISO of 100 you have to increase you shutter speed for many images. So, you can just shoot at base ISO and create the image you want in post, or you can shoot at a higher ISO and let the camera do some of the worth. Based on the images posted, I'd rather have the feed back of my histogram.

I guess you could take the image at a high ISO, say 2 stops, note the exposure, set the same exposure manually a base ISO then work in post.

Based on the images provided, or any I've seen, that would be a total waste of my time. I'm going to have to see a whole image that is better because this technique is employed, and it's going to have to be one where one image is useable, and the other isn't. Comparing different levels of bad, which is what I've seen to date is useless. It's not a thing until it can be used to produce significantly better phots. You simply can't use pixel peeping to do that. As happened in McLosky's examples. He focussed on the arts where the "invariant" section was better. But even in his own examples, parts of the "invariant photo" were demonstrably worse. With all the other variables, the difficulty of keeping the focus on the same point, minor variations in light, etc. everything I've seen falls into the category of "inconclusive to the point of being irrelevant to actual shooting." Even in the best examples, they would probably have been un-noticable in a final print.

It's theory with no practical application, and it's an extrapolation of properties that don't theoretically exist.

In the world of signal to noise, invariance is noise.

There is nothing in the whole concept of invariance that isn't explained by the superior DR of the cameras considered to be "invariant". If you have more DR, you have more to play with. When I set my camera to 16 ISO, I know all I'm doing is cutting off the lower 4 stops, but 11 stops of EV is still more than I need for many images, so I'm cool with that. Saying you can do better in post, depends completely on having a way to calculate your exposure. I've never seen a non pixel peeping image where me with a 2 second change in ISO isn't better than some guy messing around for minutes to hours calculating exposures and adjusting in post processing.

Unless you plan to sell your images for millions, it's not worth it.

Last edited by normhead; 09-04-2018 at 08:09 AM.
09-04-2018, 09:42 AM - 1 Like   #49
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QuoteOriginally posted by normhead Quote
I guess you could take the image at a high ISO, say 2 stops, note the exposure, set the same exposure manually a base ISO then work in post.
Have you really never heard of exposure compensation? Just set it to -2.0 and be done with it. Just don't combine that with auto ISO!

The whole idea is to give yourself more latitude with blown highlights. If you've never accidentally blown highlights, then you're lucky - this discussion isn't for you.

For me personally I'm just going to be less afraid to underexpose in the future, as long as I'm at a low ISO I know it isn't going to make my picture much noisier.

09-04-2018, 10:10 AM - 1 Like   #50
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It seems that the true definition of ISO invariance has been lost in all this An ISO-invariant camera is one that produces identical DR whether the ISO is boosted N stops in the camera or the shot is taken at base ISO and boosted N stops in post. It says nothing about whether boosted ISO or pushed base ISO image is better. In fact it says they are the same. And in both the boosted-ISO and pushed base ISO cases, you've lost N stops of DR.

Whether a photographer chooses to use their ISO-invariant camera at base ISO with pushing or at a boosted "correct exposure" ISO depends on balance the pros and cons of the two strategies:

Shooting at base ISO with pushing in post has the following pros & cons:
* PRO: highlights are more likely (but not guaranteed) to be preserved
* CON: the chimped image will be dark
* CON: the SOOC JPG will be dark
* CON: you need to check the amount of metered underexposure to know how much DR the sensor will offer in the post-processed image

Shooting at metered ISO has the following pros & cons:
* PRO: you can chimp the image
* PRO: the SOOC JPG is usable
* PRO: you know how much DR you'll get based on the metered ISO
* CON: you are more likely to blow the highlights

ISO invariance has nothing to do with superior DR. In both the boosted ISO image and the pushed base ISO image, you've lost the same N stops of DR.

In contrast, there are some cameras that are non-invariant where the ISO 3200 shot is somewhat cleaner than the ISO 100 shot pushed 5 stops in post. For those non-invariant cameras, it really does pay to more carefully pick the ISO (with the usual provisos about blowing the highlights). Whether a camera is invariant or not arises from the various types of noise in the pixel, analog read circuits, and ADC systems.

Even with invariance, the photographer still has to trade-off shutter speed, aperture, and either ISO-boosted or pushed DR. If picking the preferred high shutter speed (to stop motion) and the preferred narrow aperture (to get depth-of-field) implies needing to push 10 stops in post or use ISO 102400, then chances are the photographer will need to use a slower shutter or wider aperture to get a more acceptable balance between motion blur, out-of-focus blur, and image noise.
09-04-2018, 10:11 AM   #51
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I've been preaching heavy use of exposure compensation from long before you were on the forum.
What did i say that made you think that I don't use it.

My point has always been, use exposure compensation to correctly expose the part of the image that is most important, because you camera metering system doesn't know which part of the frame is important to you.

But that is about correctly exposing your image.
Everything else is secondary to that.
Back when I used a K20D, that meant great sunsets but often black shadows, But, the colour in the sky was the most important part of the image. Getting what I get with the K-1 is just bonus but still not always enough.

-2 EV


I got the best exposure for the sky but lost detail in the shadows, but, the sky was what's important.
That has nothing to do with anything, except understanding how to use your camera.
What is it you think the concept of ISO invariance has to ad to that?

If you learn anything from this thread it should be do everything you can to keep your ISO low, for noise reasons. Low ISO has always, since even film days been the best option if you could pull it off. I seem to be hearing some don't have the confidence they can pull it off.

If there's a new generation that for some reason doesn't understand that then maybe we need to do some educating.

So if you're saying was you used to boost ISO instead of using EV compensation, ya, that was bad. You shouldn't have done that.

QuoteQuote:
It seems that the true definition of ISO invariance has been lost in all this An ISO-invariant camera is one that produces identical DR whether the ISO is boosted N stops in the camera or the shot is taken at base ISO and boosted N stops in post.
Does such a camera exist?. Every curve I've ever seen has DR dropping stop by stop after base ISO. Some have relatively flat curves until maybe 400 ISO, but they all drop somewhat. The only article posted said it doesn't.

Based on my experience, I'd say the cameras with the widest DR start off with the latest curves. But there are so many possible variables, it's really a topic not worth thinking about unless exploring the characteristics of a specific camera.

If you can point me to a curve that is flat, which would mean invariant ISO I'd be be happy to check that out. What I can say for sure is if you under-expose 5 stops for no reason other than keeping the camera from doing in camera colour and noise alterations, you're probably making a mistake. You're thinking that the guys who test the output of these sensors and compensate for their idiosyncracies in camera can be out done by some software company. Maybe they can, I'd like to see examples. So far all I've seen is slight differences in contrast and noise values that in real life I wouldn't care about one way or the other.

There seem to be a lot of folks who don't understand, contrast, sharpening, definition, anything that boosts base values, causes an apparent increase in noise. That's probably what they should be talking about, just looking st available examples.

Another way of thinking of it. IN a lighting situation where a large percentage of a portion of the images would register as o luminance, all raising your digital ISO does is clip that part of the image. The reason you do that is , that based on sensor performance there is no information their to be had, so reducing DR from 13 EV to 12 doesn't really make any difference, you only needed 12, you could only record 12. Shooting 200 ISO makes absolutely no difference but you have 1/2 the light intensity on the sensor, and you are boosting noise and signal. Suggesting there is such a things ISO invariance seems to me to be physically impossible. You can clip the bottom end by under-exposing or you can clip the bottom end by increasing ISO, you get the same exposure on the same sensor in both circumstances. The only thing in question is how the camera deals with the exposure. As I said, some claim they can do better than the camera manufacturer can.

IMHO they are deluding themselves.

Last edited by normhead; 09-04-2018 at 10:45 AM.
09-04-2018, 10:46 AM - 1 Like   #52
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QuoteOriginally posted by normhead Quote
I've been preaching heavy use of exposure compensation from long before you were on the forum.
What did i say that made you think that I don't use it.

My point has always been, use exposure compensation to correctly expose the part of the image that is most important, because you camera metering system doesn't know which part of the frame is important to you.

But that is about correctly exposing your image.
Everything else is secondary to that.
Back when I used a K20D, that meant great sunsets but often black shadows, But, the colour in the sky was the most important part of the image. Getting what I get with the K-1 is just bonus but still not always enough.

-2 EV


I got the best exposure for the sky but lost detail in the shadows, but, the sky was what's important.
That has nothing to do with anything, except understanding how to use your camera.
What is it you think the concept of ISO invariance has to ad to that?

If you learn anything from this thread it should be do everything you can to keep your ISO low, for noise reasons. Low ISO has always, since even film days been the best option if you could pull it off. I seem to be hearing some don't have the confidence they can pull it off.

If there's a new generation that for some reason doesn't understand that then maybe we need to do some educating.

So if you're saying was you used to boost ISO instead of using EV compensation, ya, that was bad. You shouldn't have done that.



Does such a camera exist?. Every curve I've ever seen has DR dropping stop by stop after base ISO. Some have relatively flat curves until maybe 400 ISO, but they all drop somewhat. The only article posted said it doesn't.
The post you quoted didn't say that the DR was the same at 100 ISO and say 400 ISO.
He said the DR of the 400 ISO image would be the same as the DR of a 100 ISO image pushed 2 stops.



09-04-2018, 10:51 AM   #53
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QuoteOriginally posted by slartibartfast01 Quote
The post you quoted didn't say that the DR was the same at 100 ISO and say 400 ISO.
He said the DR of the 400 ISO image would be the same as the DR of a 100 ISO image pushed 2 stops.
Yet we have people arguing that its better to just shoot 100 ISO and increase two stops in post than shoot 400 ISO. And I've never found that to be true.

The issue here is it's really hard to expose correctly without the EV dial and a histogram, if you under-expose and correct in post processing, you lose a valuable exposure tool. Your image will appear to be dark on the back screen. The histogram will not be a reflection of your final image.
I don't see how you can create useful information leaving out such practical points.

Last edited by normhead; 09-04-2018 at 11:00 AM.
09-04-2018, 10:54 AM - 1 Like   #54
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QuoteOriginally posted by normhead Quote
I've been preaching heavy use of exposure compensation from long before you were on the forum.
What did i say that made you think that I don't use it.
I quoted the exact text that gave me that impression. Go back and look.

I didn't actually think you didn't know about exposure compensation, but the garbage you were spewing about having to do settings at one ISO then change to another ISO to take the picture just had me in disbelief.

QuoteOriginally posted by normhead:
My point has always been, use exposure compensation to correctly expose the part of the image that is most important, because you camera metering system doesn't know which part of the frame is important to you.

But that is about correctly exposing your image.
Everything else is secondary to that.
Back when I used a K20D, that meant great sunsets but often black shadows, But, the colour in the sky was the most important part of the image. Getting what I get with the K-1 is just bonus but still not always enough.

I got the best exposure for the sky but lost detail in the shadows, but, the sky was what's important.
That has nothing to do with anything, except understanding how to use your camera.
What is it you think the concept of ISO invariance has to ad to that?

If you learn anything from this thread it should be do everything you can to keep your ISO low, for noise reasons. Low ISO has always, since even film days been the best option if you could pull it off. I seem to be hearing some don't have the confidence they can pull it off.

If there's a new generation that for some reason doesn't understand that then maybe we need to do some educating.

So if you're saying was you used to boost ISO instead of using EV compensation, ya, that was bad. You shouldn't have done that.
I have always tried to use the lowest ISO that works with the shutter speed and aperture that I think the shot needs. If the picture was too dark I'd raise the ISO. ISO invariance means I don't have to be so worried about the ISO at the time of taking the picture, as long as I'm willing to work a little with the RAW - the picture will come out the same.

I've found that camera metering is inconsistent enough that blown highlights are always a possibility, even when I'm being careful to avoid them.

QuoteOriginally posted by normhead:
Does such a camera exist?. Every curve I've ever seen has DR dropping stop by stop after base ISO. Some have relatively flat curves until maybe 400 ISO, but they all drop somewhat. The only article posted said it doesn't.

Based on my experience, I'd say the cameras with the widest DR start off with the latest curves. But there are so many possible variables, it's really a topic not worth thinking about unless exploring the characteristics of a specific camera.

If you can point me to a curve that is flat, which would mean invariant ISO I'd be be happy to check that out. What I can say for sure is if you under-expose 5 stops for no reason other than keeping the camera from doing in camera colour and noise alterations, you're probably making a mistake. You're thinking that the guys who test the output of these sensors and compensate for their idiosyncracies in camera can be out done by some software company. Maybe they can, I'd like to see examples. So far all I've seen is slight differences in contrast and noise values that in real life I wouldn't care about one way or the other.

There seem to be a lot of folks who don't understand, contrast, sharpening, definition, anything that boosts base values, causes an apparent increase in noise. That's probably what they should be talking about, just looking st available examples.
ISO invariance doesn't mean a flat curve - it means one that is straight with a slope of -1.0. Raising the ISO by 1 EV should lower the DR by exactly 1 EV. Or looking at it the other way around, lowering the ISO should raise the DR by the exact same amount, until you reach the base ISO. If a camera achieves that it is truly ISO invariant.

Just so we're clear, I'm not arguing that the perfectly ISO invariant camera exists - it doesn't. But I know now that many modern cameras are close enough that underexposing by a stop or two by using a lower ISO than I would have in the past isn't going to ruin my pictures.
09-04-2018, 11:16 AM - 2 Likes   #55
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QuoteOriginally posted by Mark Ransom Quote
I quoted the exact text that gave me that impression. Go back and look..

Just so we're clear, I'm not arguing that the perfectly ISO invariant camera exists - it doesn't. But I know now that many modern cameras are close enough that underexposing by a stop or two by using a lower ISO than I would have in the past isn't going to ruin my pictures.
And therein lies the difference, I was never subject to that illusion. So I come at it from a completely different perspective. Another advantage to training. In class, we discussed, why do you under-expose, why do you over-expose, using film. Every demanding exposure has to be manipulated to get it right, and you have decisions to make that go way beyond simple Dynamic Range. The right side of the curve kills contrast, the left side of the curve boosts it. You have to decide if you want to shoot low key or high key. You have to consider blowing out parts of your exposure or not recording parts of your exposure to create black space or white space. You have many artistic decisions to make regarding where you want your exposure that invariance doesn't touch.

These are the photographic issues. Invariance... covers the basic fact that the base ISO of your camera never changes. Everything you do after that is software manipulation. Once you know that everything falls into place and you can move on to the important stuff.
09-04-2018, 11:18 AM - 1 Like   #56
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QuoteOriginally posted by normhead Quote
Does such a camera exist?. Every curve I've ever seen has DR dropping stop by stop after base ISO. Some have relatively flat curves until maybe 400 ISO, but they all drop somewhat. The only article posted said it doesn't.
Yes, and the part of the curve where DR drops exactly 1 stop for each stop of higher ISO is the ISO-invariant part of the curve. And if the camera's entire curve loses 1 stop DR per stop of ISO, then the camera is known as ISO invariant.

The flat part of the curve or the part of the curve that falls less then 1 stop DR per stop ISO is the non-invariant part where an under-exposed-base-ISO-pushed image has worse final image DR than a properly-exposed-boosted-ISO image.
09-04-2018, 11:42 AM - 1 Like   #57
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QuoteOriginally posted by photoptimist Quote
Yes, and the part of the curve where DR drops exactly 1 stop for each stop of higher ISO is the ISO-invariant part of the curve. And if the camera's entire curve loses 1 stop DR per stop of ISO, then the camera is known as ISO invariant.
Ya, it's the exposure that values that count, not the ISO.

QuoteOriginally posted by photoptimist Quote
The flat part of the curve or the part of the curve that falls less then 1 stop DR per stop ISO is the non-invariant part where an under-exposed-base-ISO-pushed image has worse final image DR than a properly-exposed-boosted-ISO image.
It's the signal amplification that counts more than the exposure.

So the only use of the whole theory of invariance, is that you need to know at what point the curve goes flat for your camera? Without a methodology for determining how much flat lining you can tolerate or what the curve is for your camera, of what use is it.

I've determined what those points are for me, using all my cameras without paying any attention to "invariance" , something no amount of discussing invariance will ever give me.

It looks good (keep doing that) or it looks awful (don't do that again) works for me.
Do I really need to know about curves, invariance, the effects of amplification, from a formal perspective? The whole of my time in photography, I've separated "need to know" with "extraneous but nice to know." It started in 1967 with my realization, I didn't need to know anything being taught in my lens design course to be a photographer..

So don't let me slow you down.

P.S. This reminds me of the old adage, "don't use digital zoom." And the same as digital zoom, you have to decide how much digital enhancement you can tolerate. For some reason there is no line like the digital zoom line on the camera that shows you when you start relying on digital enhancement rather than simply clipping the DR.

Last edited by normhead; 09-04-2018 at 12:28 PM.
09-04-2018, 01:27 PM   #58
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QuoteOriginally posted by photoptimist Quote
And in both the boosted-ISO and pushed base ISO cases, you've lost N stops of DR.
Just to clarify for me - In the case of the horse on the beach - by just lightening the shadows and keeping the highlights back and the anchors on the histogram in the same place - does the edited image still have the overall dynamic range of the original Iso 100 image?. (obviously with tonal curves in different areas).
09-04-2018, 01:32 PM   #59
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QuoteOriginally posted by GUB Quote
Just to clarify for me - In the case of the horse on the beach - by just lightening the shadows and keeping the highlights back and the anchors on the histogram in the same place - does the edited image still have the overall dynamic range of the original Iso 100 image?. (obviously with tonal curves in different areas).
If you use the same ƒ-stop and time on the same sensor the DR should be the same, as long as digital enhancement of some sort hasn't clicked in. But for all I know there could be some kind of digital enhancement even at 100 ISO, and it just increases in intensity as the ISO gets higher. But all other things being equal, the DR should be the same.

So all things being equal, if you shoot 100 ISO and +2 EV, or 400 ISO 0 EV, should give you the same exposure values and DR, but how you have to deal with them in post will be different. The only issue being, do we really know if all things are equal. I've seen a lot of assumptions, but I'm not sure anyone actually has any information. Just observations that have led them to believe one thing or another.

The thing most important to IQ and DR is the using the optimum intensity of light used to form the image. That is determined by exposure the exposure values.How much light in real terms is used to form the image.

Last edited by normhead; 09-04-2018 at 01:46 PM.
09-04-2018, 01:48 PM   #60
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QuoteOriginally posted by normhead Quote
If you use the same ƒ-stop and time on the same sensor the DR should be the same, as long as digital enhancement of some sort hasn't clicked in. But for all I know there could be some kind of digital enhancement even at 100 ISO, and it just increases in intensity as the ISO gets higher. But all other things being equal, the DR should be the same.

So all things being equal, if you shoot 100 ISO and +2 EV, or 400 ISO 0 EV, should give you the same exposure values and DR, but how you have to deal with them in post will be different. The only issue being, do we really know if all things are equal. I've seen a lot of assumptions, but I'm not sure anyone actually has any information. Just observations that have led them to believe one thing or another.

The thing most important to IQ and DR is the using the optimum intensity of light used to form the image. That is determined by exposure the exposure values.How much light in real terms is used to form the image.
I am querying about the editing of the image - not the taking of it Norm.
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