M-mode + Auto ISO?

For wildlife photography, I have always used Aperture priority mode (Av) with Evaluated metering. I would then change the ISO to get the shutter speed I want, and use exposure compensation to best suit the lighting conditions...  This work great, and is what I have been advising people to do. It is a good balance of control and speed...  you start with a higher ISO so to keep the shutter-speed high enough for any surprise action, and stop it down if the subject is still or it gets lighter. But it is not perfect, as it means you are contently having to re-asses the lighting conditions and change the ISO accordingly. You get use to it, but if you loose concentration once, you can miss the first few shots because your ISO is too low resulting in a ridiculously slow shutter-speed or your ISO is too high and you have a noisy image (the better option in my opinion).

One new feature introduced in the 5D IV that I did not have in the 5D III was the ability to use exposure compensation in manual mode (M). This new feature opened an alternative option for wildlife...  Manual mode and Auto ISO. I could use M + auto ISO on the 5D III, but without the control for exposure compensation, it basically made it useless for me. When using Av mode, I change the ISO and the Aperture to get the shutter speed I want, here I choose the aperture and shutter-speed I want, and let the camera choose the ISO. In both cases, the camera changes 1 setting (either the shutter speed or ISO) to make the exposure (which i will correct using exposure compensation). So which one do I think it better?

Av Mode

Aperture : I change this to get the shutter-speed

Shutter speed : This is determined by the camera

ISO : I change this to get the shutter-speed

M mode + Auto ISO

Aperture : I set it to what I think is best

Shutter speed : I set this to what I think best

ISO : This is determined by the camera

Having never used the M-mode and Auto ISO, I went out to a local park with some birders to test it... here are the images:

I was shooting in a forest setting, with patch cloud cover and constantly changing light (albeit not great light). This is where I think this method excels. By choosing a good birding shutter speed (around 1/1000 - 1/2000), and choosing my aperture (I started at f/4 as it was dull, but then went up to f/5.6 and f/8), I could just focus on shooting and not have to keep changing my ISO to balance the changing light, something i would have had to keep doing if shooting in Av. I was surprised how easy it was for me to adopt this method. I had envisaged many missed shots, but other than a few at the start, it was very intuitive.


  • By having the shutter-speed and aperture set, I was constantly ready for action when it comes
  • I could ignore the changing lighting conditions and focus on shooting and spotting
  • Works well in low/not ideal lighting conditions
  • Easy to use


  • When it gets light, you risk unintentional over-exposure (your aperture is too wide and shutter speed to slow)
  • You will have to adapt
  • Exposure compensation is not available on all models


The bottom line

Like all situations in life, using M-mode + Auto ISO is not perfect, but i don't find it any worse than using Av mode and setting the ISO myself (which has the drawback of extremely low shutter speeds if you don't increase the ISO). I think it is great for lower light conditions; but not that great in strong light. I will probably use M+Auto ISO in darker conditions and Av mode in lighter conditions. Try it out and let me know what you think? Do you do something different?



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