The hopper

I understand that pressing the shutter button halfway activates auto focusing and automatic exposure metering. This allows you to focus on an object and then recompose your shot ... and I do this a lot. I have recently been told that when you recompose your shot, even though you have locked the focusing function by holding the shutter button down, when you recompose your shot the automatic exposure metering is still active and adjusts to the new composition. This makes no sense to me. Why would one function (focusing) be locked while the other function (exposure metering) be active?? I could understand that you need to focus on an object, pressing the shutter button half way, and then turn the Auto Focus button on the lens to manual (basically deactivating auto focus), then recompose you shot, press the shutter button down again to activate the exposure metering, and then taking your shot working.
I also think you can go the other way and use the AE lock button. I think this process would be to focus where the final shot needs to be taken by pressing the shutter button halfway, press the AE lock button to lock the exposure metering function, then release the shutter button and focus on the object you want holding the shutter button halfway, recompose your shot and then finish pressing the shutter button.
Looking for some words of wisdom. And yes, I know I could go to back button focusing but that seems like a new world of pain that I haven't entered yet.
Thanks for the responses.

RWR Loc: La Mesa, CA

What if the part of the scene you want to expose for is different than the part you want to focus on?

pquiggle Loc: Monterey Bay California

Like you said, back-button-focus separates the two functions and makes the whole process easier. I tried it a few years ago and will never go back.

captivecookie Loc: Washington state

Try back button focusing and discover why it will make the heavens open and a glorious light shine upon your photography experience.

John N Loc: HP14 3QF Stokenchurch, UK

I just activated BBF on my 6D mkII yesterday having used it on my 60D previously. It's the way to go.
If you've got small hands (like me) check you can reach the AE-ON button easily. Seems to me it's further away than on my older camera so I'm hoping I'll get used to it.

sumo Loc: Houston suburb

My Nikon D850 Has both going on at same time. BBF and shutter focus

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

To each his own and everyone has to find what works for them. As for me, I like the traditional shutter button and use the button on the back of the camera for single spot focusing. And I have never missed a shot yet.
Like I said, the regular button works best for me and I will never go back. A female Red Winged Black Bird feeding a chick a dragonfly. Wakodahatchee Wetlands, Delray Beach Florida.

jerryc41 Loc: Catskill Mts of NY

It's really not a pain. Once you get used to it, you'll love it.

Nalu Loc: Southern Arizona

I guess I really don't get the question. Seems to me that much of a change in exposure is necessary when making very slight changes in composition. Are you getting too picky here. Perhaps you could provide an example of when you need to change the exposure in this application. Nevertheless, if you are concerned about not being able to control the exposure, perhaps you should considering going to "manual".

rdubreuil Loc: Dummer, NH USA

Why? That defeats the purpose of using BBF.

juan_uy Loc: Uruguay

As most of the replies aim to convince you to use BBF, even after you stated you don't want to go that route, I will try to explain with my limited knowledge how it works the normal/default operation that you are using (I do use and prefer BBF, but understand it may not be the answer for all).

With your camera in default configuration (all this is based on Nikon, but probably is similar if not the same, you could check your manual for differences), you have two separate ways to "lock" the auto features that you mention:

1- If you want to lock focus: you aim, half-press the shutter button and keep it like this when recomposing. Once you are ready to take the picture, you press it the rest of the way.

2- If you want to lock exposure: you aim, press the AE-Lock button and keep it pressed while recomposing AND while taking the picture.

You can combine both "locks" if needed, even in different points, if you need to recompose in such way. But remember you can move your focus/AE point.

Hope this helps clarifying things a bit. Good luck

Bubbee Loc: Aventura, Florida

I agree! The best way to "lock" in the exposure is to use manual! Much easier than stretching (my small) fingers to the AE lock. By the way, my Nikon's have the option of setting the lock to both AE and AF simultaneously or individually.

sumo Loc: Houston suburb

AGREE... I cant seem to change it....the D850 is a smart camera and Im a dumb operator

rdubreuil Loc: Dummer, NH USA

LOL... Are you sure it’s refocusing when you half press your shutter release; and that it’s not just engaging your VR?

juan_uy Loc: Uruguay

To change to BBF there are two changes necessary, defining the button that will be used for BBF and separately you must remove the focusing action from shutter release button. Looks that you missed the second one.
I don't have the D850 to provide exact steps, but for general Nikon cameras, this video from Steve Perry should help:
https://backcountrygallery.com/af-on-and-back-button-autofocus/

Good luck :)