In the below article you will find a few test around A7RIII ISO capabilities
I made a quick test to compare the ISO capability of the A7RIII vs A7RII + color rendition
Is the A7RIII performing really better ? You will see in Chapter 2
If a camera is ISO invariant it means that the camera will produce the exact same image whether you expose it correctly at shooting time with high ISO or if you underexpose it dramatically and you correct it in post processing by pushing the exposition in Lightroom
Why is this important ?
- In low light scene, you need to increase ISO, but using High ISO (especially above 3200) will always results in more noise than the base 100 ISO. If you want to avoid blur (especially with people) you also need a minimum speed e.g. 1/60
- If you have selected a too High ISO , the noise is there and it is difficult to remove it
With an ISO invariant camera it is perfectly OK to under expose by several stops the scene and to decide to correct exposition in post processing.
- The resulting image quality will be the same as the corresponding ISO
- eg Scene taken at 400 ISO , 1/60sec underexposed, if you push by +2EV in post processing it is like having shoot at 1600 ISO with same image quality as 1600 ISO
- It is like choosing the ISO of the scene after the fact to avoid pushing it it too much at shooting time
Sony sensors are in general ISO invariant , others like Canon 6D, 5D Mark III are not ISO invariant
If you shoot underexposed with a Canon 6D and you correct it afterwards , results will be much worse than if you choose directly the correct higher ISO
The Sony A7RII was already very good and considered as ISO invariant, we will see in Chapter 3 , how well the Sony A7RIII performs
2 High ISO Testing
2.1 Comparison A7RIII vs A7RII
The below test scene was shoot with both cameras on a tripod with exactly the same lens: FE 24-105mm F4 G at F11 to get max sharpness and details
ISO were selected manually from 100 ISO to 102400 ISO , the camera selecting the right speed
All Raw were processed in Capture one Pro keeping standard settings (e.g. standard noise reduction)
- Side by side you directly see that the A7RIII has more natural colors
- In term of noice no visible difference up to ISO6400
- As from 12800 ISO the A7RIII starts to be visibly better in term of noise
- As from 25600 ISO, colors of the A7RII start to degrade while the A7RIII keep natural color
- At 102400 ISO it is really striking that colors from A7RII are completely degraded while A7RIII keep good color rendition, noise is also clearly better by 0.5 Stop
2.2 Full crop A7RIII
- Perfect up to 1600 ISO
- Very Good from 3200 – 6400 ISO
- Good 12800-25600
- Average 51200-102400 ISO
Capture one pro not being the best for High ISO , if we treat it with DXO PhotoLab (once A7RIII will be supported) with the Prime noise reduction for ISO > 12800 ISO, I think we can get even better results
3 ISO Invariance
The test consist in under exposing severely the scene by 1, 2 , 3 , 4 , 5 EV and to see if by correcting exposition in post processing (Capture one , Lightroom…) we can get same results as if we would have set the correct ISO settings
For the below scene the correct exposition for F11 , ISO 100 is 8 seconds
ISO 100 – 8 Seconds
if we shoot at ISO 1600 the same exposition is giving a speed of 0.5 seconds
For the test I have fixed ISO to 100 ISO and taken shoots at
- 8 sec = correct exposition
- 4 sec = -1EV
- 2 sec = – 2EV
- 1 sec = – 3EV and
- 0.5 sec = – 4EV
The below shoot taken at ISO 100 – 0.5 sec is therefore underexposed by 4 stops
Correcting the exposition in Capture one Pro by + 4EV
You can see that there is no visible difference between the 100 ISO + 4EV or the 1600 ISO, the A7RIII is really well ISO invariant
As a comparison I also include the same scene made with A7RII and also pushed by 4EV , you see that the results are also very good but the A7RIII is a clearly better in this test
Note that I would have liked to test 5 or 6 stops under exposition but Capture one pro (only one supporting Raw from A7RIII at that time) is limited to correcting 4 EV max
- A7RIII winner for its better color rendition, very stable at all ISO (up to 102400 ISO)
- A7RIII winner for noise above 12800 ISO with up to .5 Stop difference vs A7RII
The A7RIII is ISO invariant and perform even better than A7RII in that domain
You can safely underexpose in low light scene and recover everything in post treatment
The dynamic range offered by the raw of the A7RIII is (one) the best available end of 2017
Well done and very interesting.
It would have been nice to have section 2.2 summary for the A7RII as well, though I suppose it can be deduced from section 2.1.
A question about the A7RIII ISO invariant feature.
If I under expose an active scene (wedding, sports) to freeze motion with high shutter speed, in theory, I should be able to reclaim proper exposure in post processing without adding additional noise.
Compared to if I originally selected a higher ISO to support the correct exposure for the faster shutter speed. Is that correct?
What seems to be the limit with the ISO invariant feature and how does it differ from other Sony cameras? I have A73.
You won’t have less noise if you push in post processing : you will have same noise as it was exposed normally
Some other non sony show more noise if pushed in post and there you must expose correctly
With sony it does not really matter
The only advantage to under pose is not too use systematically to high iso if you use manual iso
Since we have iso auto min shutter speed function. It is quite useless now to underexposed
Personnalité I use a iso auto min shutter speed of 1/125 for a7iii and let thé body manage iso
I go up to iso 12500 in general so anything pushed to an equivalent of 12500 will give same result as if it was selected within camera