Flash compatibility w/ Rebel XTI

Discussion in 'Beyond the Basics' started by cfello16, Mar 1, 2007.

  1. cfello16

    cfello16 TPF Noob!

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    I have a Rebel XTI with a Bower 724afc flash and am having some trouble with it. Whenever I have it attached my optimum shutter speed goes down dramatically and I have been unable to shoot anything faster than 1" at a respectable ISO. If I remember correctly, when I first bought the flash/camera package...it worked fine. I'm wondering if it is broken or I need to adjust some of the settings. Any ideas?

    THANKS!
     
  2. EOS_JD

    EOS_JD TPF Noob!

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    Does the XTi have FEC (flash exposure compensation) capability. Canon's E-TTL system tends to underexpose in a lot of situations so FEC is needed to compensate for this.

    For that camera I would recommend either a Canon 430EX Speedlite Sigma EF-500 DG Super (Canon version). These are the two inexpensive units that allow FEC.

    Buying cheap units may not always be the best solution. You'll save money in the longer run buying the better sigma or canon units. The Sigma Super is very good value.
     
  3. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    I checked this site but they didn't list that flash.

    What do you mean by "my optimum shutter speed goes down dramatically" ?

    Shutter speed doesn't really have much to do with flash exposure...as long as you keep the shutter below the max sync speed of the camera, which I believe is 1/200 on that model.
     
  4. cfello16

    cfello16 TPF Noob!

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    Thanks for the response. By optimum shutter speed I mean I can't shoot anything faster than 1" based on available light. I bought the flash with my camera as a package on ebay...so I'm not expecting much out of it since it was bundled, but at least to be able to shoot faster than 1"! All I'm saying about the exposure is that when I attach the Bower flash (as opposed to using the built in flash on the camera)...my light meter is telling me I need to shoot at around 1" in order to let enough light in...know what I mean?
    thanks!
     
  5. cfello16

    cfello16 TPF Noob!

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    It does have EFC...I'm assuming I should turn it UP?

    thanks!
     
  6. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Oh, I see.

    Seeing as this is an off brand flash (and a brand I've never even heard of)...the camera probably doesn't know that it's on there....and that's why it's giving you long shutter speeds, because it thinks that it has to use ambient light only, to make the exposure. FEC only works for the built-in flash or a Canon brand flash.

    When the built-in flash is used, the camera knows that it's on...and uses a pre-flash and E-TTL technology to determine the exposure.

    You can use off brand flash units...but you will probably have to put the camera into M (manual) mode. Does your flash unit have 'auto' settings and a little 'eye' on the front? If that's the case, then you should have a power setting on the flash...maybe a slider or a switch with a couple of different settings. What you do, is set the flash and match the settings on the camera. So, for example, you would set the flash to give proper exposure at F4 @ ISO 100...then you match those settings on the camera, in manual mode. That will control the flash exposure. The shutter speed will have no effect on the flash exposure (just keep it under 1/200)...however, the shutter speed will control the amount of ambient exposure that will show up. So if you want more 'background' to show up in your shot...use a slower shutter speed. If you want less 'background'...then use a faster shutter speed.

    You flash might also be a strictly manual flash. In which case, you would need to know the GN (guide number) and then you would calculate the aperture to use based on the distance to the subject.

    I had been using an old off brand 'auto' flash for years. Once you figure it out and know how to work it...it's great. However, I recently purchased a Canon 430EX flash...and it's really, really great. Much less thinking about the flash and I can use the FEC on the camera to control the flash power, rather than having to change the settings on the flash and or camera and worrying about how they match etc.
     
  7. cfello16

    cfello16 TPF Noob!

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  8. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    From that chart, you can figure out the aperture setting to use for normal exposure.

    If you subject is 10 feet away (3 meters) then at
    ISO 100 set the aperture to F8
    ISO 200, F11
    ISO 400, F16
     
  9. cfello16

    cfello16 TPF Noob!

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    Thanks for the quick responses.
    You the man!
     
  10. cloose

    cloose TPF Noob!

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    It should also be noted that the cameras light meter will always show exposure for ambient light only, no matter what kind of flash is attached.
     

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