ISO Invariance

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Wim Bosch

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Steve question

Am somewhat confused trying to shoot my photos to ETTR now I'm reading about ISO Invariance Ask who use this in the real world for wildlife holdings of D5 and D850 and can someone give me an example how to use the exposure that angle

Thanks in advance for comments

Wim
 
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The best advice? Shoot a proper exposure whenever you can. ETTR isn't nearly as valuable as people think it is - especially if you're using ISO to achieve it, since ISO is simply applied gain. In my tests, I was never able to see a difference between normal and ETTR images except at base ISO.

ISO Invariance is, in my opinion, a more useful technique - but only sometimes. I leverage it when trying to preserve highlights.

For example, maybe I have an animal in a tree with a bright blue sky behind it. If I expose for the animal, my sky blows out. However, if I expose so my sky is just a bit shy of clipping and leave my animal dark, I have options. I can then go back to my computer, pull down the highlights and bring up the shadows / exposure and possibly have a shot I can use. The key is to keep your ISO as low as possible in that scenario.

However, not all cameras are ISO invariant and they won't all tolerate that procedure. You D850 will (ideally at around ISO 400 since that's when the secondly amp kicks in) but the D5 will not. The D5 is not ISO invariant at all and usually does not tolerate shadow pulls that well.
 
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That's been my experience too. ETTR was a really good advice 15 year ago when we did not have dual gain sensors, we did not have complex on and off sensor noise reduction algorithms etc... today there is nothing wrong in doing it (if done correctly - folks often confuse ETTR and clipping highlights...) but I really don't know that one gains much with ETTR versus letting the camera handle the shadows "behind the scenes" to keep them clean of noise on a shot eposes "to the middle", when you know that ETTR always has the risk of that critical 1 or 2% brightest pixels clipping.

I have far more use for Iso invariance as long as it's not overdone - overall I trust Nikon to embed better shadow management in the camera than what Lightroom can do so like Steve recommends I try to get it as right as I can in camera rather than on purpose be 3 to 4 stops under because "in theory it will be the same in the end..."; but yes, if I am going to err on one side with newer Nikons it will be to underexpose a bit because the I know there is sone flexibility there, more so than on clipped highlights (where there is none obviously). And also because I learnt with shooting slides and one thing you learnt to do with slides was to ALWAYS override your ISO by 1/3rd of a stop because slides have zero tolerance for overexposure - so I am at home right where I started if I slightly underexpose to take advantage of ISO invariance. But I don't do the 3 to 4 stops under exposures - I don't think those shots are as easy to salvage as "experts" make it sound.

By the way, I didn't feel that way when I shot the Canon 1Dmk4 and 1DXmk1 - on those cameras, any 1/3rd of stop of DR and cleaner shadows I could squeeze out by pushing histograms to the right was worth its weight in gold. But on the newer Nikon's I'd much rather worry about composition and let the camera do what it does best. I know, I'am lazy :)
 
If you look at the shadow improvement graph for your camera at photonstophotos.net you see the d850 is partially invariant but not the d5. Link below. Either way there is no point to using ISO to push to the right. Contrary to popular belief ISO is not part of exposure. Exposure is only aperture, shutter speed, and maybe scene brightness. So if you can expose to the right using shutter speed or f stop that is good, but doing it with ISO not so good.

 
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bleirer said:
If you look at the shadow improvement graph for your camera at photonstophotos.net you see the d850 is partially invariant but not the d5. Link below. Either way there is no point to using ISO to push to the right. Contrary to popular belief ISO is not part of exposure. Exposure is only aperture, shutter speed, and maybe scene brightness. So if you can expose to the right using shutter speed or f stop that is good, but doing it with ISO not so good.

Click to expand...
Thank you for this link. So is that graph basically showing with a secondary amp kicks in? Example: as long as below ISO 400ish on D500 and D850 there is very little to roughly no "harm" from a shadow pull? Above that point, there is only about 1/2 stop of degradation as compared pulling vs capture in camera? I am not following the ev values given when you hover over a point in the charts.
 
KCPhoto said:
Thank you for this link. So is that graph basically showing with a secondary amp kicks in? Example: as long as below ISO 400ish on D500 and D850 there is very little to roughly no "harm" from a shadow pull? Above that point, there is only about 1/2 stop of degradation as compared pulling vs capture in camera? I am not following the ev values given when you hover over a point in the charts.
Click to expand...
I'm not an expert, just like you I find it interesting. An EV is basically one 'stop' of shadow improvement compared to base ISO.. Here is a good explanation link but don't give up the reading gets easier if you stick with it. My limited understanding is that ISO eats highlight dynamic range, each doubling of ISO costs one stop of highlight loss, but shadows can improve with ISO to a point. People think iso causes noise but it is really the lowered exposure ISO forces the meter to indicate in terms of shutter speed and f stop that causes the noise. After 400 on the d850 you can get the same brightening in lightroom as in the camera with ISO but in lightroom you don't lose the highlights. But shadows continue to improve with the D5.


 
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