Flash in AV and TV mode

mkpatilmkpatil Registered Users Posts: 85 Big grins
edited November 28, 2006 in Technique
In P (green or priority or auto) mode that is used along with FLASH the camera logic is clever enough to find the correct or most optimum lens aperture and also lens speed. But in AV mode with FLASH we set the aperture, therefore we have done half the job for the camera, why doesn't the camera do the second half and find the correct speed? Of course for non FLASH setting it works perfectly, but I am taking AV with flash. Same for Tv. Am I missing something?

Thanks,
Milind

Comments

  • asamuelasamuel Registered Users Posts: 451 Major grins
    edited November 17, 2006
    This is a fairly common question. Its a big field but one that is intuitve once the readings done.

    I am assuming here that you have a canon and a hot shoe flash.....thats a big assumptionrolleyes1.gif

    If so this thread is great for you!

    http://www.dgrin.com/showthread.php?t=33703

    Be sure to read the links to photonotes and pathfinder and it will become clear.

    If I'm wrong about your camera, you should post the specifics in a reply. Good luck!
    where's the cheese at?

    http://www.samuelbedford.com
  • pathfinderpathfinder Super Moderators Posts: 14,703 moderator
    edited November 17, 2006
    Mkpatil,

    Welcome to dgrin.

    You do not list the camera and the flash unit you are using, nor did you list them in your personal profile, so I have to guess what equipment you are asking for help with............ For simplicity's sake, I have ASSUMED you are using a Canon DSLR and a Canon flash like the 430EX. Most of my comments will also pertain to a Nikon system I believe, but I no longer own or use modern Nikon gear, so I may need some help if Nikon is your equipment.

    A lot of folks, new to digital photography, assume they can just use the auto settings with flash with a DSLR and things will be ducky, but quickly learn that they need to know more precisely how to use a flash with a modern DSLR.

    P mode is designed to allow HANDHELD shooting, so it will not allow a shutter speed less than 1/60th of a second. Av mode with flash uses the flash for the forground and the ambient light for the background, so the shutter speed can be set by the camera for up to 30 ( yes that's right ) thirty seconds.. Hence, you need to watch the shutter speed as you may need/require a tripod with flash in Av mode. You may find you need to shoot in Manual Mode ( I know this sounds like the exposure may not be correct, but the Canon OEM flashes are smart and will set the correct exposure) to get the control of the camera settings for the image you want.

    I have written about this several times - one thread is here - http://www.dgrin.com/showpost.php?p=292152&postcount=7

    Read it and let us know if this has answered your questions.

    I shoot Av mode a lot for fill flash, so much that I do not even give it a second thought - most of my shots in bright sunlight with a near subject may have fill flash shot in Av mode --

    This is one such image I remember

    29581359-M.jpg

    And another

    110893714-M.jpg

    Notice how the exposure is balanced between the subjects shaded face and the brightly sunlit background. How did I capture that?
    Pathfinder - www.pathfinder.smugmug.com

    Moderator of the Technique Forum and Finishing School on Dgrin
  • mkpatilmkpatil Registered Users Posts: 85 Big grins
    edited November 27, 2006
    Thank you very much for helping me understand. Sorry I could not reply earlier as I was on vacation at home baby sitting.

    Yes I use Canon EOS-1D Mark II N Digital with 540EZ so similar flash.

    Thanks,
    Milind
  • pathfinderpathfinder Super Moderators Posts: 14,703 moderator
    edited November 27, 2006
    Bear in mind, that if you use Av outdoors in sunlight for Fill flash, with a fairly large aperture, you may end up using shutter speeds higher than 1/250th.

    You will then need to set your EOS Flash to High Speed Synch, since your camera's native synch speed max is 1/250th. I usually leave my strobe in High Speed Synch so I don't have to deal with it when I go outdoors or if I switch to Manual mode.
    Pathfinder - www.pathfinder.smugmug.com

    Moderator of the Technique Forum and Finishing School on Dgrin
  • sirsloopsirsloop Registered Users Posts: 866 Major grins
    edited November 27, 2006
    I pretty much exclusively shoot in M when when using flash. After you get some experience using the unit, you get a feel for how well the shutter speed will expose the background. The camera is smart enough to figure out exposure most times without flash. The flash is smart enough most times to figure out flash exposure. I really think the decision should be left to the photographer on how well lit the background is.

    400D, 580ex+lightsphere, EF 35mm f/2, iso 100, f/8, 1/40th, handheld.

    IMG_7082.JPG


    I usually end up shooting higher iso and more open aperture to obtain faster shutter speeds. In this case I was pretty much laying down so the camera was rock steady - and the cats OBVIOUSLY aren't in a hurry to move!
    http://www.tallmanphoto.com
  • mkpatilmkpatil Registered Users Posts: 85 Big grins
    edited November 28, 2006
    Thanks a lot.
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