AE Lock and Back Button Focusing

[Wirefox]

Most of the old hacks will know this but I thought I would share with so many new comers to CiC

Using AE Lock with Back Button Focusing
I have been toying with the idea of setting my 40D for back button focusing - That is where the camera is configured to use the AE lock (*) button on the back of the camera for autofocus. However, after reading THIS I am not so sure it will fit my style of shooting. The main point that made me think again is this.

When the back button is configured to initiate autofocus (Menu C.Fn IV-1 - AE Lock/Metering + AF Start AND MNU C.FN IV-2 Enable) pressing the shutter halfway down locks the exposure setting so that you can meter off one area of the scene, recompose and focus on an other area without altering the exposure. That is fine but it is worth considering that if you wish to keep that exposure setting for the next shot you cannot take you finger off the shutter - you must release pressure to the half down shutter position again. A bit fiddly with cold or gloved hands.

And a question for the more tech minded; If I switch the AE lock from back button to shutter can I lock exposure in other camera modes than One Shot and evaluative metering. I say this because when the shutter is set to focus and hold the exposure setting (default) the camera only holds exposure in one shot evaluative metering modes. For any thing else including spot focus the metering is not locked by the depressing the shutter half down (you have to keep the back button (*) depressed). You would assume that when you switch buttons that the shutter behaves exactly like the AE Lock button but I cannot find any positive reference to confirm this.

[Colin Southern]

Hi Steve,

I know that a lot of people re-assign AF to a back button, but I'm not one of them -- I just could never see the need.

In terms of metering, if you're using anything but spot-metering then metering and recomposing is unlikely to change things much, unless it's an unusual scene, and even then results are likely to be inconsistant. In those situations where you want consistency, and total control, and not have to worry about reassigning buttons etc ...

... just stick the camera into manual mode.

Works for me.

[bambleweeney]

Ditto. Back button autofocus doesn't really work for me either, plus I suspect I'm one of many who use my left eye on the viewfinder so it's a bit fiddly with my face in the way to use this as an option. Half press on the shutter works fine for me and the AE button is used to lock exposure (or to release the exposure lock). Find this works better for me when I need to meter off one part of a scene but focus on another. Mine's set up so that exposure lock stays on until I press the button to release it so it will keep the same exposure for a number of shots - handy up until the point you forget to release it, change the point of view and wonder why the exposure's all over the place

[Blazing fire]

I agree with Colin and bambleweeney.

Use manual mode to lock exposure.
Assign that AE/AF button to AF lock only.

[Donald]

I know I don't need to because I shoot in manual all the time, but I do use back button focusing.

It's just one of those things you get used to. And from the time I discovered you could do it and set it accordingly, I've just got so used to it (and I'm a left-eye on the viewfinder person). To do anything else now would not feel right (until, of course, I then got used to that).

It also gives me something to do with that button since I don't use AE lock!

And a question for the more tech minded; If I switch the AE lock from back button to shutter can I lock exposure in other camera modes than One Shot and evaluative metering. .... You would assume that when you switch buttons that the shutter behaves exactly like the AE Lock button but I cannot find any positive reference to confirm this.

I don't know. That's because I'm not at all tech-minded. For me it would very much be a case of try it and see.

[Colin Southern]

And a question for the more tech minded; If I switch the AE lock from back button to shutter can I lock exposure in other camera modes than One Shot and evaluative metering.

Try it and find out

[Blazing fire]

I know I don't need to because I shoot in manual all the time

Donald, how do you manage to shoot in manual all the time? Don't you ever use apeture priority, or programme mode?

Do you disable auto focusing too?
Do you set the WB using the Kelvin scale (as opposed to the preset ones)?

[Donald]

Donald, how do you manage to shoot in manual all the time? Don't you ever use aperture priority, or programme mode?

Just practice, I suppose. I never use any of the other modes. Did try it on Tv once when in France and the Tour de France was passing by where we were staying - but it was a miserable failure. But that's also probably because I have never practiced sports action photography.

But, for the most part, I'm not shooting situations where there is much action or movement and I need to be getting right on the button quickly. As I've said in previous posts, my shooting habits tend to be rather long and laborious. I might be at a location for anything up to 45-60 minutes, wandering around, setting up the shot, checking composition, watching the sky, etc, before I press the button.

The act of getting ready to press the button is, probably, the most pleasurable part of photography for me.

Shooting in manual in these circumstances is not an issue.

Do you disable auto focusing too?

No, although I do a lot of stuff in Liveview, using Manual focusing.

Do you set the WB using the Kelvin scale (as opposed to the preset ones)?

I don't bother about WB in camera. It's always on auto. I have a WhiBal card and even though I shoot for B & W, I always take a couple with the WhiBal in frame so I can then correct it when I begin to process, so that my conversion to B & W is starting from a position of 'correct' colour information.

Hope that makes sense.

ps - Should maybe have added. I also spot meter all the time.

In relation to any given shot, you will have made a decision about, either, what shutter speed or aperture value you want to shoot at. So that's set in your mind. From there it's question of identifying the spot from which you are going to take your spot meter reading. And, from there, it's a matter of deciding how you want to expose it and setting the other value (aperture or shutter) accordingly.

That's also how I work when I am wandering around with camera in hand as opposed to on tripod.

So that's how my little mind operates. But it might not work for everyone else.

[inkista]

Using AE Lock with Back Button Focusing
I have been toying with the idea of setting my 40D for back button focusing - That is where the camera is configured to use the AE lock (*) button on the back of the camera for autofocus.

Actually, I think by default, if you do back-button, it's the AF-ON button that's assigned to trip AF start/stop, while the * button remains AE Lock.

It's only on the older and dRebel bodies that don't have an AF-ON button where you have to choose between AE Lock or AF-start as the function for the one button you do have. It takes another custom function setting to swap the functions of the AF-ON and * buttons on the 40D/50D. But you still have both buttons available to you, although it's awkward to try and use both at the same time.

Like Donald, I rarely use AE lock and I do use back-button and focus lock, so I tend to swap the AF-ON and * buttons, and set the * button to be AF-start, rather than stop. Not having to be forever holding that damn halfpress to lock focus is a serious blessing both when I'm birding, and when I'm shooting events, or in a situation where I'm likely to use full-time manual focus to finetune the autofocus.

When I use back-button, I'm most typically shooting birds in flight, where the lighting conditions can change so quickly as you spin about that if I am going to lock the AE, I'll probably only be doing it for a burst, anyway, so the shutter half press works fine for me. I do bless the ability to store custom modes on my 50D, though, so that I can quickly and easily swap back and forth between back-button AF and the default shutter half-press behavior. I like using both ways of locking the AF.