Get it locked down! We explain your camera's exposure lock modes in detail

Canon PhotoPlus EOS SOS Exposure Lock
Evaluative metering with One-Shot AF uses the AF to identify where to meter from, Partial metering as shown, meters at the centre without automatic exposure lock (Image credit: Brian Worley)

Exposure lock is a term that applies to different kinds of exposure and how long you might want the exposure to be locked. EOS cameras have two independent metering systems, one for ambient light (AE-lock) and another for a camera-controlled Speedlite (FE-Lock). Some cameras combine the lock of both flash and ambient, while others feature individual lock buttons for flash and ambient.

If you’re using One-Shot AF, you can unwittingly lock the exposure; when focus is achieved in this mode, cameras automatically lock the exposure with Evaluative metering. This makes sense as Evaluative is using info from the focus system to determine the position of the subject, and recomposing might change the brightness of the scene by including more brighter or darker areas – but not change the exposure on the original subject. 

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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.