I'm a bit confused the by exposure locking function. I wonder if anyone could enlighten me please?
As I understand it:
When I semi-press the shutter button, the camera starts 'metering', i.e. seeing how much light there is and setting the ISO, shutter speed and aperture (depending on the mode) appropriately. As this uses battery power, after a (configurable) amount of time it stops doing so.
Now, if I assign "AE lock (Hold)" to a button, then when I press that button the values of ISO, shutter speed and aperture will be frozen.
However, once metering stops, the exposure lock will end.
So what I don't understand is: Why is the camera still metering if the settings have been locked? And therefore, why can't they just remain locked indefinitely?
#1. "RE: Exposure locking" In response to Reply # 0
Brighton and Hove, GB
I didn't realize that AE lock (hold) does not hold indefinitely, so I've learned something. You can customize the meter off delay (custom setting C2) to make it longer if it's troubling you. Evidently metered values are kept in transient memory: when metering and AF go off to save battery, these values are lost because the memory they were in is powered off.
I've recently got into the habit of shooting in M mode and I'm trying to use the AEL button for AF-ON so I don't see this issue.
#2. "RE: Exposure locking" In response to Reply # 0
Kuala Lumpur, MY
I have my AE/AF - L button mapped to AF-On and my Fn button mapped to AE lock (Hold). I used AE lock (Hold) extensively for bright outdoor conditions. With my limited experience, allow me to have a crack at your inquiries:
>When I semi-press the shutter button, the camera starts >'metering', i.e. seeing how much light there is and setting >the ISO, shutter speed and aperture (depending on the mode) >appropriately. As this uses battery power, after a >(configurable) amount of time it stops doing so.
Actually the camera doesn't start metering when you semi-press the shutter, it starts metering immediately & continuously when the camera is turn on & lightmeter is on until the lightmeter turn off (control by c2 custom function). Try it, turn the camera on, point it at dark & then bright area without half pressing the shutter. You can see the exposure values changes depending on what mode you're in.
>Now, if I assign "AE lock (Hold)" to a button, then >when I press that button the values of ISO, shutter speed and >aperture will be frozen. > >However, once metering stops, the exposure lock will end.
This is correct, the exposure lock will cease once the meter is off either by the delay you set in c2 or by turning off the camera. If you set the delay in function c2 to No Limit then the meter doesn't turn off until you turn off the camera.
>So what I don't understand is: Why is the camera still >metering if the settings have been locked?
Put the camera in Manual, point it at different brightness and you will see the meter in the viewfinder moves. Activate the AE lock then the meter is 'frozen'. Now I know we don't exposure lock in Manual which is in a way a permanent exposure lock, this is just to illustrate the point. Whether the meter still meters while locked, I think only a Nikon engineer and/or expert out can verify. Any out there that can help us with this?
My own guess is, the camera will keep metering in the background as long as the meter is on but when you lock the exposure only the values are locked. I agree with Gary that turning off the meter will erase the lock values stored in memory thus answering your next question. There might also be software and/or hardware limitation on having the meter still on but not metering or the engineers thought it's not necessary to have such behavior.
>And therefore, why can't they just remain locked indefinitely?
The hazard of locking the exposure even after the camera turns off is the last exposure might not be what you want when you turn camera back on. Worse when you want to grab a quick candid shot and shot it in wrong exposure. If you wish the have the exposure lock as long as you have your camera on, set c2 to No Limit. This will have some effect on your battery life though. And if you want the exposure to lock indefinitely even after the camera is turned off and back on, you can always switch to manual.
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