Ae-lock and Re-Compose

Started 2 months ago | Questions thread
alcelc
alcelc Forum Pro • Posts: 16,178
Re: Ae-lock and Re-Compose
1

Jcbailey wrote:

Bill Ferris wrote:

Jcbailey wrote:

I'm confused on how AE-lock works. I was adivsed and also tried this. Walk into a room point at what i want to capture, lock the exposure with AE-lock. re-compose and take the shot. in theory the shot should have the same exposure as when i locked it. I don't see this.

Did you read this reply to one of your previous threads?

https://www.dpreview.com/forums/post/65423995

for example. i went into a dark room and found some light. i metered the light and my Shutter was at 1/200 to see if it was right i metered the dark spot and it was 1/60. so i Ae-locked the 1/200 from the light locked it re-composed and the shot came out dark.

Metering off the light in the dark room would have set the exposure & lightness of the scene 1 to 2 stops below optimal. When metering in a space to use as a reference for exposure and ISO settings, it's best to find a surface that's middle gray in tonality. If that's not available, if very dark or very light are what's available, you'll need to dial-in exposure compensation to compensate for metering off surfaces that are 1 to 2 stops off middle gray.

my camera focused again while i pressed the shutter all the way down and took whatever shot it wanted. I was in AV mode with a fixed iso.

What happend?

As for the autofocus, were you in single-shot mode or continuous AF? Also, was your camera setup so the shutter release button activated autofocus or so a button on the back side of the camera activated AF?

Last one was spot metering i think. this one was evaluative

Evaluate metering ( or called Matrix metering, Multiple metering etc by different brand) indeed is to take the exposure reading (the brightness) of the entire frame, and according to the algorithm of the camera to give priority on certain areas (degree of brightness) that the engineers behind your camera thought it will produce the best result. This reading will also be set as center (0ev) of the exposure meter. A set of parameters will be setup for a combined result which can produce an output for such level of brightness. (Under AEL, that set of parameters will be fixed used despite what meter reading it will get.)

Therefore the camera will take into consideration of the shadow and highlight areas in the frame on top of the focusing area for a RELATIVELY more balance result (due to different priority of different brands, down to models, the result could be difference).

Spot, as you know shall concentrate on a smaller area to measure the brightness, it is best for the aimed target since majority of its surrounding brightness condition will be ignored. Center weight will use a larger size of area to take measurement and so partial of the surrounding of the aimed target will be considered for a relatively more balance result than Spot, but more limited than Evaluate.

As from above, the size of area to take the metering will affect the result. The contrast of the frame (the darkest and brightness) and also how podominant of lightness condition (a lot of darkest or bfightness) will also affect the measured result. Spot and Center weight will also be affected by where you take the reading.

You can test it very easily. Switch on a tiny table light (best to use a small light blub), or light a candle in a dark room:

  1. Point your cam to the light, use S mode (you use shutter speed here) and manual ISO at 200 (to use a single variable here for easier understanding). Note the suggested parameters, then
  2. move the camera away from the light source, again note the parameters.

You could find a faster shutter speed (less amount of light is allowed to reach the sesnor) will be used in the 1st set of metering. Spot metering should use the fastest shutter speed, following by Center Weight, then Evaluation.

You should also find a slower shutter speed will be used in 2nd set of metering...

To your case, you use AEL to lock the set of used parameters which was taken at the light source!

You might have misunderstand that when you do AEL, you are not telling your camera to shoot for a result similar to the brightness condition as when you pointed towards the light source. You are just ask the camera to use the set of parameters that the camera will use to shoot for the light only.

Wish this might help.

and AE-lock. to me they are diffrent. plus i haven't said anything here in weeks or the last one was a week ago

Thanks for the reply though

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Albert
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