AE Lock button question

[soup]

fancy-schmancy DSLR stuff. So much to learn.

Having a lot of fun with it, but there is some frustration trying to figure out the settings. Going through the manual, again and again.

I hope the AE Lock button is the answer I'm looking for on this go-round.

Let's say there's a rock that I want to place in the lower right of the photo, and I want the focus to be on it, not the oh, um, er can of tomatoes in the center of the frame.

I focus on the rock, push the AE Lock button, turn the camera a bit so the can of tomatoes is in the center of the frame, then take the picture (within the 4 seconds time allowed after AE is pushed) and the rock will stay the focal point of the shot. Is that correct?

--- and, if so inclined, can I also push the DOF button (within the 4 second time frame) to see what I've got, or will that negate the AE Lock button? (hope that additional bit didn't make my question too confusing. If so disregard this part.) ---

In other words,
Is AE Lock used to temporarily overrule the lens?
or is it something else entirely?

[soup]

1. Ok, that wasn't it...

Boy, did I read that wrong.

Went down to the pond to test it, and it didn't produce the results I thought it might. As soon as I shifted the camera a bit, the focus moved off of where I was trying to put it.

So, can someone tell me - What does the AE Lock button do?

Is it a brightness lock as opposed to a focal lock?

I'm so lost.


on edit:
Found this:
http://www.karbosguide.com/books/photobook/chapter18.htm
Written so even I can understand it. Makes sense, now.

[NV Whino]

2. I don't know about your camera, but on mine

which is a Nikon D100, you can shift the focus area from the center to the top, bottom, left or right. That frequently solves the "what to focus on" problem for me.

Also, I think focusing on the left area and continuing to hold the shutter release in the half punched position while you recenter the viewfinder will work with most cameras.

[ET Awful]

3. Typically, AE Lock is "Automatic Exposure" lock.

It will lock the exposure to it's current setting, allowing you to recompose without the aperture or shutter speed changing (depending on the mode you have the camera in).

Sometimes those buttons are multipurpose though (for instance the D200 and D300 have a button that is labeled AE-L/AF-L and you can change the function from within the menue.

NOTE: ON MOST SLR cameras, if you push the shutter release button halfway, it will focus, then, keeping the button halfway pressed, recompose your shot, then press the button the rest of the way to activate the shutter. This will give you the focus on the original target but allow you to move that target within the frame.