Is there a way to use the AE Lock and Hold feature (I have a mark iii) and keep the hold while toggling focus points? Every time I toggle I lose the metering that I locked. I know I can first find my focal point and then meter, but it would be super convenient if there was a way to Lock Exposure and then be able to toggle and then take the shot. Please let me know as I have a shoot in the morning, thanks in advance!!
Yes, you must look through the viewfinder to move the AF point and (very important) DO NOT touch the AF point selection button. You can move the AF point around (as long as you're in any mode that allows selection of AF points) as long as the focus system is "awake". In other words, if you look through the viewfinder and half-press the shutter button to wake up the system, just use the 8-way navigator and you'll notice you can move the point anywhere you want.
So...
Point the camera, half-press the shutter to meter. When you see the meter reading, press the "*" button on the back of the camera (upper right corner) and that's the AE lock. You'll see the * appear in the viewfinder near the left (next to the battery charge level indicator in the viewfinder.)
Now that the exposure is locked, it will stay locked as long as you don't let the focus or metering system shut down. Normally that's somewhere around 5 seconds. You can half-press the shutter button to extend the time -- which will cause the camera to re-focus but it will also reset the time on the AE lock. Remember... DO NOT press the AF point selection button or it will unlock.
Use the 8-way navigator to move your focus points around and you'll notice the exposure remains locked in.
You must look through the camera to select the AF point -- do not use the LCD screen (because that would require pressing the AF point selection button which would unlock the AE lock.)