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Flash compatibility for Rebel XT Digital Camera

Steven Young , Sep 21, 2007; 05:11 p.m.

I have a Vivitar 2600-D Auto Thyristor Flash. Can I use this flash with my Canon Rebel EOS XT Digital camera? If so what should I know< if not, Why not.

Responses

Bob Atkins , Sep 21, 2007; 07:19 p.m.

With a Wein Safe Sync it should be OK.

Even though the XT should be safe up to 250v and I don't think the 2600 sync voltage is higher than that, you may still want to use a Safe Sync. It never hurts.

Carol Sutton , Sep 22, 2007; 10:55 p.m.

Hi Bob & Steve & all, Thank you for your question & answer above..:) I am a newbie and have just got a 400d eos and want to either purchase a flash (with limited funds), or use one I purchased with a pentax slr. Its a SUNPAK multi dedicated thyristor auto 2000DZ. I also got an ACHIEVER 300DX with the pentax,(which says it is for a pentax program). *I would like a flash to give me an overall fill of my outdoor/indoor photo's without having to enter full-time college and have a degree in photography..even though I am studying intro courses etc..:)Please forgive my ignorance too..:) Many thanks..:)

Steve Dunn , Sep 23, 2007; 11:47 a.m.

Carol, have a look at the hot shoes on your two flash units. This page has some info about how to tell a dedicated flash from a non-dedicated flash, and the potential problems of using a dedicated flash with a camera of a different brand. The description of your Sunpak sounds like it probably has (well, has available; chances are you have to buy each one individually) a series of interchangeable adapters to go on its foot so that it can be used with a variety of cameras, but the chances that it will have one that works with a Canon DSLR are pretty slim.

If the flash unit is nondedicated (or if you make it nondedicated by covering the extra connectors with something nonconductive like electrical tape), then the next question is whether the trigger voltage is safe. Have a look at this list to see if your flash units' trigger voltages are listed. If they're under 250V, they're OK on the 400D; if they're over 250V, they're not (and you'll need to use something like a Safe Sync). If the flash unit isn't dedicated and you happen to have a voltmeter handy, you can measure it yourself; the first page I cited has instructions.

A nondedicated flash can't communicate with the camera, so everything the 400D's manual says about flash metering does not apply. What sort of flash exposure you'll get will depend on what features the flash has.

  • Auto flash (sometimes called thyristor flash, particularly on older models; your Sunpak sounds like it fits this one): the flash has a built-in light sensor, and it will decide for itself how much light is required. Because the camera and the flash can't communicate, the flash doesn't have any clue what settings you're using on the camera (ISO and aperture), and a correct exposure can't be determined without this information. You'll either have to use some sort of input on the flash to tell it these things, or you'll have to set the camera to whatever settings the flash wants. The manual for the flash will tell you which one applies to your flash.
  • Manual power setting: the flash may let you tell it how much light to emit, typically in fractions (full power, 1/2 power, 1/4 power, etc.) It's up to you to figure out what the right setting is. Full power works the same way as described below. 1/2 power is one stop less than full power; 1/4 power is two stops less.
  • Neither of the above: if your flash doesn't offer either of these options, then it is a basic unit which will simply fire at full power every time you fire it. It's up to you to figure out what aperture to use on the camera to get a correct exposure. If you're using the flash as your main light source, it's simple; find the flash unit's guide number (it's in the manual) for whatever ISO you're using, divide it by the subject distance (the GN is measured in either feet or metres, and you have to use the same unit for your distance measurement), and that's the aperture you set. If you want to use the flash for fill light, then you'll have to do some thinking about how many stops below this you want the fill to be. Play around a bit; try one stop below (i.e. stop down the aperture one stop more than the GN calculation suggests), try two stops below (i.e. stop down two stops beyond what the GN calculation suggests), see what works best, and once you've sorted it out in full stops, don't be afraid to try half stops.

Carol Sutton , Sep 24, 2007; 12:29 a.m.

Wow, thank you Steve - I'll be back to comment again, after educating myself with all your fantastic input above! (I just had to acknowledge you, thank you again)...((((smiles)))). Take care and I will watch, be learning & chat real soon..:)

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