Backbutton focusing, flash and the 400D

[Overread18 6]

Well I recently read about the backbutton focusing custom function and setting it so that one can have the shutter half depressed and not have the AF activate - and instead having the * button (on the 400D) activate the AF.
However the * butter also activates the flash exposure lock for ETTL metering with the flash. Which means if backfocusing is enabled I can't (far as I can see) be able to also use ETTL flash exposure lock to fire a preflash to allow the flash to meter the scene before me.

Does anyone know a work around for this?

 

[table1349]

Sorry, disregard my post. Mis-read yours. Thought it was a 40D instead of the 400D.

 

[Overread18 6]

I was going to say page 32 had little pictures telling me how to hold the camera

anyone got any ideas though? I can really see the focusing change being a benefit but not if I have to lose flash control (or does this mean I have to learn manual flash methods?

 

[LarryD]

Hmmm.......seems to me that I would rather just turn the lens off and manually focus on the subject..

In any event, here is a Canon Tutorial on AE Lock, perhaps it will be useful:

Canon AE Lock Function

 

[table1349]

I was going to say page 32 had little pictures telling me how to hold the camera

anyone got any ideas though? I can really see the focusing change being a benefit but not if I have to lose flash control (or does this mean I have to learn manual flash methods?

Sorry about that. Page 32 in the 40D manual talks about the dedicated AF button on the back of the body next to the * button. Works for the 40D but not the 400D. My bad. :blushing:

 

[Tighearnach]

Well I recently read about the backbutton focusing custom function and setting it so that one can have the shutter half depressed and not have the AF activate - and instead having the * button (on the 400D) activate the AF.
However the * butter also activates the flash exposure lock for ETTL metering with the flash. Which means if backfocusing is enabled I can't (far as I can see) be able to also use ETTL flash exposure lock to fire a preflash to allow the flash to meter the scene before me.

Does anyone know a work around for this?

Hi

I'm just wondering in what circumstances you would want to use the * button for AF instead of half pressing shutter button?

 

[Overread18 6]

Often when I am zoos and the like its possible that the AF will lock onto the bars of a cage rather than the animal - this is often the case when there is a barrier before the bars/wire of the cage - so one cannot put their lens up against it. In these situations its preferable to have AF on in case the subjects make sudden movements, but the constant locking onto the wrong item in the viewfinder can make getting shots impossible. The same can also happen when focusing into reeds, bushes, trees -anywhere where something gets between the camer and the subject, since AF is based around focusing on the closest thing.

Now of course one can turn af off - but then one has to turn it on again in a blink to get action shots in focus again - and the af on/off switch is often not in easy reach of the lens (or if its cold its not possible to twich the button with a glove on .

Thus with AF on one is always in a problem when you come to press the shutter -as the af tried to help and fails. Thus having the button on the back means one can choose to use af or not for a shot. Its something that I like the idea of but really have to test it in the field - the biggest problem is that losing the flash auto exposure settings might hamper me considerably for flash usage with this method (as I really don't know manual flash usage).