how long does exposure lock last?

Hi

If I use exposure lock to set the exposure, the * disappears from the viewfinder after a few seconds. Has it reset to standard exposure, or its still there but the display isn't (like when the exposure meter comes up when you half press for only a while)?

Also, does it reset after taking the shot? If you want to keep the exposure for multiple shots (eg backlit portrait) is the only way to use manual exposure to lock it in?

Finally, I've read that you should prefocus then use *. But that seems fiddly to me as I have to keep the shutter half pressed all the time. Does it matter when I press *? i.e does the shutter half press override it?

Locked exposure settings when using the * button vanish after 4 seconds. A detailed description of its use can be found in the manual. I encourage you to read it, then read it again.

Exposure readings/settings in Av and Tv mode are adjusted every time you recompose your photo and are only locked when you snap a photo or when you press the * button (for four seconds). I think you will also have to use manual focus to lock in an exposure/shutter speed setting for multiple shots without using new exposure readings. Finally, there are plenty of threads on here that already discuss the pros and cons of prefocus using the * button. A search will yield many, many results.

4 seconds isn't very long I'd have thought it'd stay on (and perhaps cancel with second press)

Is that one reason why some people like the custom function? so instead of exposure lock, focus (perhaps recompose), you can focus, then expose/recompose/shoot​?

you're right, I need to read some more, but its invaluable to have real people speak about their experiences sometimes, compared to a very dry, fact based manual

I've got a 300D and the manual is absolute rubbish in this area. I'd also like to know when locking exposure whether you have to keep the shutter pressed half way to maintain the original focus lock or whether you can press *, recompose, focus and shoot?

For FEL lock on the 300D, the manual is slighty (only just) better in that it explicity states that you must hold the shutter half way to maintain the original focus lock whilst you press (and hold?) * on the subject to expose for.

I would be supprised if these two are different, does anybody know?

Also if the operation for FEL is correct in that you have to hold the focus lock, that must mean you can't be set on AI focus because it'll just track when you move the camera to lock FEL!

I think Canon have made this about as ergonomically impossible as they could.

Yes, that is correct. By holding down the * button the exposure would be locked, or for 4 seconds after removing your digit from the button.

so you can hold it and it'll stay there?

I can press the shutter button halfway/fully *after* pressing * and it won't re-expose - it'll just focus? and if I keep my finger on * after shooting, it'll keep the exposure while shooting more shots?

These problems are somewhat resolved by moving the focus to the * button and using the shutter button for exposure only. You can hold the shutter button to maintain exposure and still use the * button to refocus (while holding the exposure).

I'm lost now!

I think I've got FEL, but for normal exposure lock, do I still have to hold the shutter button half way while I lock the exposure on something else? I would be surprised is this is true because the * stays in the viewfinder even if I re-focus after locking the exposure.

I agree focus on * would be nice, if my camera supported it!

Right, done some experiments with my 300D to clear this up.

It seems that you don't have to do any focusing before you lock the exposure with *. You can go ahead and lock the expsoure with *, recomose, focus and shoot. Provided you do all this within the 4 seconds you're fine.
If when you press *, you keep your finger on it you can re-focus/shoot as many times as you like and the exposure will be locked, provided you keep * pressed.

This works exactly the same for FEL as for normal exposure lock, so the manual for my 300D is misleading as it insists you have to hold the shutter button halfway from the initial focus, this just isn't true.

Hope this helps, it has me.

Also, AFAIK, the timers for FEL and AEL won't time out as long as the DoF preview button is pressed.

If 4 sec's is not enough, than after you get the reading, just change it to the same shutter speed and aperature in manual, then you can have the settings from that meter reading until you yourself change it.