problem judging correct exposure with flash

Discussion in 'Photography Beginners' Forum' started by Gazman, Aug 22, 2008.

  1. Gazman

    Gazman TPF Noob!

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    Today whilst my brother was visiting with his kids i decided to take a photo or 2 with his kids and my daughter.

    It was indoor with not the best light, so flash was definitley required.

    Now my problem is, how do you judge correct exposure when using flash, because obvioulsy when using the light meter it doesnt allow for the flash, so i can be largely under-exposed(according to light meter), but once flash goes off, it exposes the picture correct (hopefully).

    Is it just a case of trial and error? i`m guessing not, as that seems a little to ameturish.
    Normally i don`t mind messing around trying to get settings right, but when i have a 1 year old sat infront of me, it begins to limit my window of oppurtunity ;).

    heres the only pic i managed to get off after messing around a few times.

    It seems a little underexposed, and obvioulsy compisition wise, not the best.

    [​IMG]
    Oh, and wb is out i know, like a fool i left it on sunny from earlier today :meh:
     
  2. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

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    Any modern DSLR with an onboard/ matching external flash will perform TTL (Through the lens) metering. Turn the flash on, take the picture. Older, manual flashes will have a calculator or scale on the back which, given the known distance from the subject, will tell you what aperture to use.
     
  3. Gazman

    Gazman TPF Noob!

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    so, if i understand, i can use the shutter speed and aperture that i choose, and even if light meter is reading it largely underexposed, once i take the picture the camera will add enough flash to expose it correct?
     
  4. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

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    Yes, to a point. All cameras have a maximum flash-sync speed (that is a maximum speed at which flash will operate correctly). For most current DSLRs, that's in the 1/200th - 1/250 of a second, although some go as high as 1/500 of a second. With respect to aperture, while a flash will allow you to use greater DoF, there are limits. Read this overview of flash guide numbers: http://www.vividlight.com/Articles/1214.htm for a better explanation.

    Generally speaking, for the type of image shown above, 'Auto' or 'Program' mode will give you good results. Your best bet however is to thoroughly read your camera's manual and the manual for your external flash (if you have one). Good flash exposure is actually more difficult to achieve than most people think.
     
  5. Gazman

    Gazman TPF Noob!

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    Thanks for reply.

    As of yet i only have the s*!!%y pop up flash with my camera.
    I do plan on getting external flash all in good time, but i want to be able to feel comfortable actually understanding how to get good shots, and how to use the camera better first.

    I havn`t studied how to use flash effectivley yet (aside from reading manual of course), i only use it when needed at the moment, plenty of time for that :)

    Another link to add to my ever growing photo favourites tab :)
     
  6. sburatorul

    sburatorul TPF Noob!

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    that flash on the camera can be really useful at times if used correctly and if you take the time to improvise some bounce device for it. when i don't have time to make myself a bounce thingy (maybe i will post a picture of it just to demonstrate what i am talking about) i just use a paper napkin wrapped around it and it works better(there are diffusers for built-in flashes if you are interested and they are cheap)

    now i don't know about other cameras but my d60(which i absolutely love), when i put in aperture priority mode and pop the flash, if the shutter speed is long it automaticaly sets it to 1/60 and adjusts the flash acordingly to get a corect exposure. i usually shoot in manual mode(control freak... i admit) but that gave some sort of clue on what settings to use with flash (but they differ from situation to situation - mostly trial and error until i will get the hang of it)
     
  7. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    Remember that to the light meter "correct" means middle gray tone. As the photographer you have to interpret the world somewhat for the meter. For instance the scene in the photo you posted looks brighter than middle gray to me: light wall, light couch, light skin, mostly light clothing. The meter, whether measuring ambient light or flash exposure, is going to try and underexpose the scene, because it wants to make bright tones middle gray. You have to dial in some extra flash exposure compensation, which tells the meter that you want it exposed brighter than middle gray. For a scene like this I'd probably dial in +2/3rds flash, take a test and see if I need to adjust that.
     

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