High Iso: how far a photographer should go?

Shooting at high iso is a topic highly commented. Some believe it is certainly overstated. And indeed, it is far from being so important in photography. At the same time, we should know the limits: how dark can it be? How far can we go at high ISO when shutter speed is critical? Not from a purely technical perspective but to stay consistent with our overall artistic approach. Some photographers may shoot only at very low light but that’s unusual. Most of us are just shooting at high ISO and at the same time also at lower ISO value. So, high ISO noise level is just a constraint we need to deal with.

The problem is to know for each of our camera we own the ISO limit at which we should shoot. Indeed, too high noise or too much underexposure leads to unacceptable image quality. The usual approach is purely empirical: when you believe the noise level has become unacceptable, you just don’t shoot at this value or above.

The problem with this approach is twofold: it can be biased, there is no tangible comparison until you use a scientific measurement of noise and it does not consider the fact that you may shoot with different kind of cameras (from smartphone to drones, DSLR, Full frame or small sensors). However, regardless of sensors, a photographer should keep consistency from a noise-to-signal ratio between the cameras (assuming noise-to-signal a proxy of noise level). Nobody cares which camera you have used for a photoshoot. But all images should be delivered with a similar if not equal quality level irrespective of the sensor.

I have started to measure SNR (Signal-to-Noise Ratio, proxy of noise level) for a given camera at different iso levels. The process is simple:

  1. Take photos at different ISO with the same histogram of the same object or landscape (no over or under exposure between images) but with different cameras. Images must be as similar as possible.
  2. Define a limit above which you believe noise is too high for your best sensor (Nikon D750 in my case).
  3. Define the ISO limit for each camera for the same value of SNR to ensure consistency in the quality

Results on the graph below:

Based on this method, I concluded I can shoot up to 12’800 ISO with my D750 maximum and if possible, not above 6’400. It is not that the image is not acceptable above, it is just to be sure shooting at high ISO has no significant impact on image quality according to my own standard. The SNR is indeed stable up to 6’400 ISO.

But with the Nikon D7000, an older APS-C camera, it is no more than 1’600 ISO. With my APS-C mirrorless Fuji X100s, it is 3’200 ISO (due to a more recent sensor). And with my compact Panasonic LX100, no more than… 400 ISO.

This has been a surprise. Indeed, I used to shoot way above 400 ISO with my compact but indeed, at a closer look, it is not without consequences on the image quality.

It is also proving how some sensors are just much better because their SNR stays stable (D750 or LX100) before dropping at very high iso while other are decreasing steadily (like X100s or D7000). with the former, you just shoot at whatever ISO you want below a given limit whereas with the later, you try to keep ISO as low as possible every time.

Please contact me if you want to know more about this approach and how to shoot at high iso without image quality loss.

Leave a Reply

Your email address will not be published. Required fields are marked *