ISO invariance understanding it - just checking something

Started 2 months ago | Discussions thread
Flat view
CESA Regular Member • Posts: 367
ISO invariance understanding it - just checking something

Hi all,

I am looking at the sony a73 and its ISO performance and read noise and would like to know something.

I want to assess what is the correlation when using the exposure/highlight/shadow slides with this plot and ISO setting. I don't know if I will make myself explain correctly but will try.

DN perfornace

If we look at that plot from any of them but in particular the A73, analysing from the ISO point of view it means that from ISO100 to ISO500 it is ISO invariant and the from ISO640 all the way up it is also ISO invariant?

If so, I have a couple of questions here:

1. How do we correlate the exposure slide and the highlights and shadow sliders with this in terms of noise? I will explain:

a) If I underexpose, by say 2 stops, a picture using ISO100 in post to get a correct exposure I would bring the exposure up by 2 stops without losing details and introducing noise?

b) This would be equivalent to have shot at ISO 400 if I had aimed to correct exposure using same shutter speed?

c) So by doing this one can protect highlights.

2. Now another scenario would be: I increase the ISO to say ISO400 in order to have an higher shutter speed, almost like shooting to the right of the right. This would still be in the first range of ISO invariant section (assuming that what I said above is correct).

a) So this means that in post I can bring down the exposure 2 stops (equivalent of have shot at ISO100) and get the correct exposure having protected the highlights? This would mean I would be introducing noise in the shadows right?

b. Again I guess that this would have been equivalent to have shot at ISO100 without losing quality and adding noise right?

3. Now in this scenario I Am curious to know. Say that you shot at ISO400 and have underexposed by 1 stop. So we are at the edge of that ISO invariant interval. Done this to increase a lot the shutter speed.

a) Now in post I would need to increase the exposure by 1 stop. Would this mean that we would jump to the next range of ISO invariant interval? Would we expect more noise? Probably a different colour artefacts only?

b) So would you also jump to the next interval if you had shot at ISO100 and increased the exposure by 3 stops?

4. I guess that looking at the plot we are better off shooting at ISO640 instead of ISO400 looking at the ISO performance no?

ISO performance

Now another question related to point 4 is. If we shoot at ISO640 and if we bring down the exposure to the correct place as long as we decrease it by 1 stop at least we are good because we will not end up on ISO400 which has a worst performance. Is this thought correct?

Another question is regarding the highlight and shadow recovery. I know these can add noise however how do they corralate with the ISO perforance and DN read? The same analysis in terms of increasing or decreasing the exposure and ISO invariance and dn read noise applies? Do you know what I mean?

Thanks in advance.

Flat view
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow