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by garik

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Actually it's my dad's lens that he bought many many moons ago to use with his old Canon T70. I dont have a flash but have borrowed his to try out, but he mentioned that some flashes will send too much voltage down to the camera and can damage the camera.. that's the last thing i'd want to happen to my new baby.

Thanks all Greg

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2 Answers 2

up vote 2 down vote accepted

The 277T (I think you have an extra 7 in your model number) should be fine, as referenced in Photo Strobe Trigger Voltages. If you're still not sure, you could always email Canon support to find out, but a quick Google check shows that it is being used on modern Canon dSLRs.

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The trigger voltage list is really a great effort, but I'd take the information there very carefully, as I assume most of the people who provided the input don't know that their DMM cannot actually measure the voltage correctly. See my answer to this question earlier. –  ysap Dec 28 '10 at 20:42
    
@ysap - I don't disagree, hence the mention of Canon support. However, in this particular case, comments on various Canon forums and other websites back up the assertion that this flash is fine. –  John Cavan Dec 28 '10 at 21:03
    
Well, from my experience with the Sunpak flash, Canon were reluctant to confirm the Rebel XT is high V safe, and just advised me to use a safe-sync or else I will damage the camera. In this case, thought, the OP has a canon flash so they may be more willing to cooperate. –  ysap Dec 28 '10 at 21:42
    
I'd guess that people measure with an oscillograph/-meter. PS: Same as my answer, only with the correct link. Thank you, "community" for severely downvoting a obviously mis-pasted answer instead of silently deleting ... –  Leonidas Dec 28 '10 at 22:59
    
@Leonidas - what do you mean by "same as my answer"? –  ysap Dec 28 '10 at 23:28

Yes, if it is an old flash, it is possible that the trigger voltage is around 200V. However, according to some information from Chuck Westfall (Canon USA official), all bodies since the EOS 20D should withstand this voltages (I don't have the link, but you can search Google and it will pop up in one of the many forums).

To be on the safe side, you can get yourself a safe-sync device that decouples the electrical contact between the flash and the body.

Anyway, if you want to be sure about the voltage, you can test with a multimeter. The problem is that most of them have a too-low input impedance so the reading is false. You need one with 10MOhm at least. I just got a cheap DMM from Walmart that was actually able to correctly measure the 190V on my old Sunpak flash, where 2 other meters failed and read around 6V. I know it should be 190V b/c it was confirmed by an industrial FLUKE meter and later on by Sunpak representative.

The Walmart one is from the Automotive shelf and named INNOVA EQUUS 3300. It specifically mentions 10 MegaOhm in big writings on the package.

This post may help: http://forums.dpreview.com/forums/read.asp?forum=1031&message=26638040.

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Here's a safe-sync device from B+H. If you trust your circuitry skills, you can also build one yourself. I would highly recommend buying a commercially-made one; there's less chance of something going wrong and frying your camera. –  Evan Krall Dec 29 '10 at 6:47

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