Canon camera skills: Use Aperture Priority mode when light levels are changing

Use Aperture Priority (Av) to control depth of field with custom settings to avoid slow shutter speeds (Image credit: Brian Worley)

Aperture Priority (Av) mode is one of the most popular creative modes, allowing photographers to choose the depth of field, while the camera chooses metering and shutter speed. 

Wondering how to use the aperture priority mode? One of the limitations is the shutter speed range extends as far as 30 secs. As a result, when shooting in low light, blurred photos often result due to camera shake and subject movement.

One option for most cameras is to set the camera to Auto ISO. This causes the camera to factor in the focal length of the lens and raises the ISO to avoid camera shake as much as possible, especially in low-light situations. But if you shoot with a 24mm lens a 1/30 sec shutter speed is likely, which is still a little slow for photos with moving subjects.

More advanced cameras provide extra ways to limit the shutter speed with Av. Change the minimum shutter speed for Auto ISO with the program or Av. In Auto ISO the camera uses the focal length of the lens to determine the minimum shutter speed, but this setting lets you increase the minimum shutter speed, either in relation to the focal length or a selected value. In low light with flash, the ISO is locked to ISO400, which renders this option slightly less useful. The camera ignores your minimum shutter speed setting and chooses shutter speeds for correct exposure with ISO400.

Limit the shutter speed in Av mode

One of the best ways to limit the shutter speed in Av is by limiting the shutter speed range. Once you limit the range, you also need to activate the safety shift with ISO to avoid underexposed shots in low light. With the ISO safety shift activated the camera will override the selected ISO when the shutter speed reaches the minimum you’ve chosen. If you use flash, then it is best to choose a fixed ISO, not Auto ISO. 

The ISO will be adjusted and not limited to ISO400 with flash. If you pick this method, use a custom shooting mode, C1/C2/C3 to make a copy of Av and implement the settings. Other modes outside of the custom mode will then allow the full range of shutter speeds to be selected.

Limit shutter speed range, and enable safety shift with ISO to avoid slow shutter speeds (Image credit: Brian Worley)
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Brian Worley

Brian is a freelance photographer and photo tutor, based in Oxfordshire. He has unrivaled EOS DSLR knowledge, after working for Canon for over 15 years, and is on hand to answer all the EOS and photographic queries in Canon-centric magazine PhotoPlus.