HelleGuy Loc: Boston

This is how I have my D750 set up.

hcmcdole

On my Canon 7D with the shutter pressed halfway (I've already assigned the AF-ON to be the only focus button), the meter will change as I pan across a scene but I can hit the AEL button (* button on this camera) and it will lock the meter for a few seconds so I can move back to my subject and take the shot (can't think of many instances I've use it but I know there are plenty of tricky situations - I usually review the shot and shoot again with a different compensation in these situations).

pete-m Loc: Casper, WY

That's what I do and it works well for me.

Bud S Loc: Logan Ohio

yes the shutter button still locks wxposure. If I want to meter another area, I compose to that area, hold shutter button half way down to lock exposure, recompose and shoot. Of course lock focus with back button before hand. Simply take two extreme lighting situations and play with it.

jeep_daddy Loc: Prescott AZ

If you don't have any more buttons to assign, then take note of the settings when you are getting a meter reading. Then use exposure compensation when you recompose and take the shot. This will become second nature after a while. You won't even have to look at your meter. You'll just see that you have a bright back-lit area and you'll just bump your exposure compensation up 1 ½ stops or so.

Peterff Loc: O'er The Hills and Far Away, in Themyscira.

This is clearly a camera specific question. We have quite a few Sony experts and advocates on the forum, I would imagine some of those can help you and would be happy to do so. If you haven't sorted this out yet, try re-posting using a title such as "SONY BBF: Help requested". That should even wake up the Sony users from their usual somnolent state!

amfoto1 Loc: San Jose, Calif. USA

On what camera? Different brands and models have different control setups.

On my Canon cameras, which have all been set up with BBF for many years, metering starts and runs with both with half-press of the shutter release and when the BBF button is pressed.

AE Lock is another matter... it stops and locks metering.

Earlier Canon cameras didn't have an AF On button on the rear, so we had to use the */AE Lock button for BBF. Setting BBF up on those we have a choice of AE Lock all the time or AE "unlocked" all the time. The latter is the better setting, because there are just too many times when you really don't want AE Lock (particularly if shooting types of subjects that really call for BBF). If and when you needed AE Lock you could cancel BBF temporarily... Or you could just make mental note of your settings, switch the camera to M and set it manually... same result as AE Lock (though not quite as quick). In fact, switching to M has one advantage over AE Lock... because that cancels itself after something like 15 seconds... while settings made in M don't self-cancel.

Later Canon cameras have an AF On button that can be used for BBF and leaves the */AE Lock button available to use. (Note: 40D and 50D models have AF On and * button on the camera body itself. But if used with BG-E2/BG-E2N battery grip it is still necessary to assign the function to the * button because that grip only has that.. it doesn't have the AF On button.

On all Canon models with both buttons that I've used, if preferred it's also possible to swap their functions. Personally I do this because the */AE Lock button is larger, more prominent and closer to my thumb. I focus every shot I take and only occasionally use AE Lock... so it makes more sense to me to use the * button for BBF. Also, I'm in the habit of using the * button for focus from using earlier Canon models.

Other brands and models of cameras are likely different. But, if your particular camera doesn't have another button to which you can assign AE Lock, and you need that occasionally, I'd simply suggest you get in the habit of switching to M instead. It's easy and accomplishes exactly the same thing.

While it's a useful feature at times, I don't recommend having AE Lock full time, if that's an option. That will almost certainly cause incorrect exposures in certain circumstances.

AE Lock is used to pre-set the exposure settings, while remaining in one of the auto exposure modes (aperture priority, shutter priority, program or manual + auto ISO... and possibly auto flash).

AE Lock is used much like "focus and recompose" (which is made more possible with BBF), except AE Lock is with the metering and exposure settings.

burkphoto Loc: High Point, NC

That's one way it can work on most cameras... It is often configurable.