1 Introduction

In the below article you will find a few test around A7RIII ISO capabilities

High ISO

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

ISO Invariance

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

I get

 

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

 

4 Conclusion

High ISO

• 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

ISO Invariance

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