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-   -   Use of AE/AF Lock on S2 IS (https://forums.steves-digicams.com/canon-21/use-ae-af-lock-s2-83420/)

Jackco Mar 12, 2006 1:04 PM

Hi all,
Can anyone explain/give examples when to use AE/AF lock?
Isnt the same as spot metering ?

Thanks.

mchnz Mar 14, 2006 2:24 PM

Spot metering only meters the one spot, you have to find a spot that is representative of the result you desire. AE lock will take into account more points in the frame, you may be able to approximate a good exposure by just pointing the camera in the general direction of the important features - you don't have to spend time finding a representive spot.

Using AE/AF lock if the subject is off-centre, or if you want to be ready for the action by pre-focusing etc.

Tullio Mar 15, 2006 2:47 AM

When you press the shutter release half way, the camera does two things: it calculates the exposure based on how you have the camera AE setup and it pre-focus also based on camera settings. Now, imagine you are taking a picture of an object but for whatever reason (lighting condition, special effects you wish to obtain, etc.) you want the camera to measure the exposure from a different part of your scene and then recompose and shoot. In this case, without being able to lock the exposure you are stuck because the moment you point the camera to the area you want it to measure the light from, your camera will also AF so when you recompose, the subject you actually want to photograph may end up totally out of focus. Now, the AF lock you use in case you want the subject being photographed not at the center of the frame. You then depress the shutter half way pointing at the main subject to lock the focus and then recompose and shoot.

Jackco Mar 15, 2006 6:39 PM

Thanks both for your tips.
But with the person scenario, you can also move the "focus" box to the person and then focus on the person instead, yea?

Tullio Mar 15, 2006 7:01 PM

If the person is close enough to the area you want to meter. Brian Peterson talks about AE lock and one of his examples, he points the camera to the sky to meter the light, locks the exposure, re-compose and shoot. In this case, I don't think you'd be able toaccomplish what you suggested.


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