How do AE-L/AF-L and AF-ON differ from focus-and-recompose, and when should you use them?
Asked 4/23/2012
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I usually shoot by putting the subject under the center focus point, half-pressing the shutter to focus and meter, recomposing, then taking the shot. I’ve learned this is called focus-and-recompose.
What other common ways are there to focus and lock exposure? In particular:
- What does the AE-L/AF-L button do?
- How is that different from AF-ON/back-button focus?
- Why would you want to separate focus from exposure metering?
- When is focus-and-recompose a bad idea, and when is selecting a different focus point better?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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You lock exposure when:
Something very bright or dark close to the subject is throwing the metering off - you can get close so that the bright spot is out of frame (or at least far enough from the center so it doesn't effect metering), lock exposure, move back into position, focus and shoot
The subject itself is very dark or bright - you can lock exposure on a gray card or another medium brightness object than remove it and shoot the subject.
You don't want to expose for the subject - for example for sunset photos you may want to expose for the background and add flash to light the subject
You can't use the center focus point but you are still metering for the center - if you have a very shallow depth of field (for example, with a 50mm f/1.8 wide open at close range) recomposing will throw your subject out of focus
Personally, I prefer to switch to manual mode in those cases instead of using exposure lock.
If you find yourself in those situations often it makes perfect sense to have focus and exposure on different buttons (that's what "back button focus" or AF-ON is for) since if you already meter and focus separately why should you bother with always metering then focusing and keeping buttons half pressed.
Originally by user2481. Source · Licensed CC BY-SA 4.0
user2481
14y ago
0
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Your method is focus-and-recompose, and it’s common because it’s fast.
AE-L/AF-L lets you lock exposure, focus, or both, depending on camera settings. Typical uses for exposure lock:
- bright/dark areas are fooling the meter
- the subject is unusually bright or dark
- you want to meter one area but focus on another
- you want to expose for the background, then light the subject with flash
AF-ON/back-button focus separates focusing from the shutter button. With this setup, pressing the shutter no longer refocuses; you focus only when pressing the AF-ON (or reassigned AE-L/AF-L) button. Many photographers like this because they can focus once, recompose, and shoot repeatedly without the camera trying to refocus each time.
Focus-and-recompose can be a poor choice with very shallow depth of field, because moving the camera after focusing can shift the plane of focus enough to miss the subject. In those cases, selecting a different AF point is often more accurate.
In general:
- use focus-and-recompose when speed matters and depth of field is forgiving
- use another AF point when precision is critical
- use AE lock when the meter is being misled or when focus and exposure should come from different parts of the scene
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