Backbutton focusing, flash and the 400D

Discussion in 'Beyond the Basics' started by Overread, Feb 6, 2009.

  1. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    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?
     
  2. gryphonslair99

    gryphonslair99 Been spending a lot of time on here!

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    Sorry, disregard my post. Mis-read yours. Thought it was a 40D instead of the 400D.
     
    Last edited: Feb 7, 2009
  3. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    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?
     
  4. LarryD

    LarryD TPF Noob!

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    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
     
  5. gryphonslair99

    gryphonslair99 Been spending a lot of time on here!

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    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:
     
  6. Tighearnach

    Tighearnach TPF Noob!

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    Hi

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

    Overread has a hat around here somewhere Staff Member Supporting Member

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    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).
     

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