Flash Sync Question Rebel XT

[Zoinac]

I have a digital rebel xt. I'm considering eventually purcahsing some studio lights (depending on money... sigh) but, currently with my at home make shift versions, I'm not getting any joy.

As it is right now, I have some 1970's relic that I stole from my grilfriend's dad's camera bag when he wasn't looking. It's a small thing that won't fire at all from the rebel xt. But, I can use it with it's optical sensor... sort of.... The problem I have with this is that I have to use the built in flash to fire it (pressing the 'go' button makes for trouble at normal shutter speeds). This, I thought would be simple, but nope.... For some reason, if I fire the flash, the built in flash goes, so does my slave flash... but in my picture only the built in flash appears. I can set the shutter speed way down, and no change. It appears as if somehow the built in flash pre-fires my slave flash.

The only way I can combat that problem is pressing the FEL button, that works, but, I have to fire a pre-flash for every shot, and that means waiting for the flash to recharge.

I'm assuming it has to be some sort of metreing thing.. but I dunno? My concern is if I'm having this problem with this little thing, A) will I have that problem with studio strobes if they are optical slaves? and B) If I do have that problem with studio flashes, can you avoid it by using a speedlight?

Any help I can get would be awsome...

(also, as a side note, I can't get this old thing to fire off the hot shoe... which is probably cause it's older than me, but if I get a pc-cord adapor for my rebel, to fire studio lights, will that work?)

[cdifoto]

I have a digital rebel xt. I'm considering eventually purcahsing some studio lights (depending on money... sigh) but, currently with my at home make shift versions, I'm not getting any joy.

As it is right now, I have some 1970's relic that I stole from my grilfriend's dad's camera bag when he wasn't looking. It's a small thing that won't fire at all from the rebel xt. But, I can use it with it's optical sensor... sort of.... The problem I have with this is that I have to use the built in flash to fire it (pressing the 'go' button makes for trouble at normal shutter speeds). This, I thought would be simple, but nope.... For some reason, if I fire the flash, the built in flash goes, so does my slave flash... but in my picture only the built in flash appears. I can set the shutter speed way down, and no change. It appears as if somehow the built in flash pre-fires my slave flash.

The only way I can combat that problem is pressing the FEL button, that works, but, I have to fire a pre-flash for every shot, and that means waiting for the flash to recharge.

I'm assuming it has to be some sort of metreing thing.. but I dunno? My concern is if I'm having this problem with this little thing, A) will I have that problem with studio strobes if they are optical slaves? and B) If I do have that problem with studio flashes, can you avoid it by using a speedlight?

Any help I can get would be awsome...

(also, as a side note, I can't get this old thing to fire off the hot shoe... which is probably cause it's older than me, but if I get a pc-cord adapor for my rebel, to fire studio lights, will that work?)


Sounds like your focus-assist is firing off the slave(s) instead of the actual flash firing the slave(s). On the XT, focus-assist is achieved via the flash...

You could try using an external flash like the Sigma EF-500 DG Super or something with IR focus-assist so it doesnt prematurely set off the slaves.

OR...you could try manually focusing. That'll eliminate the AF-Assist altogether.

[24Peter]

What's happening is, your on-camera flash fires a pre-flash before the main flash and that's triggering the strobe's optical sensor. Almost all digital cameras do that (fire the pre-flash before the main flash. I think even the external Speedlites do.) Anyway the solutions is simple (and about $40): get one of these:

http://www.adorama.com/MRDS1.html?searchinfo=ds-1&item_no=2

Works like a charm. Has two settings so it can work as a slave for a digital flash (ignores pre-flash) or as a slave for a regular strobe. It's also super sensitive - much more sensitive than the optical sensor in many external flashes/strobes. (If price is an issue, I think there are other similar devices that sell for less but I haven't used any those.)

[TheObiJuan]

disable the on camera strobe via custom function or going to 'No Flash' mode.

[Zoinac]

Well, cdi-buy, if you are refering to the annoying af-assist barrage of flashes in low-light conditions, that hasn't been the issue. I can't get it to work even in great conditions. at leaste not well. But, to ensure that as not being the problem, I just tried it via manual focusing. Same problem, only get the one flash in the photo. (unless I do FEL first)

24Peter, how fast is this first-second flash action? When I observe the camera, it appears that it only emits one flash. I could be wrong, it's bright... lol. But, looking at that clever solution you presented, seems to me that this might be a common problem?

[24Peter]

24Peter, how fast is this first-second flash action? When I observe the camera, it appears that it only emits one flash. I could be wrong, it's bright... lol. But, looking at that clever solution you presented, seems to me that this might be a common problem?

Common yes, since this is by design on all digital cameras. Problem, well only if you're trying to trigger a slave with the on-board flash. Basically the pre-flash is imperceptible to the human eye (well not sure if that's entirely true since I think I've seen it a couple of times) but it's there or you wouldn't be having the problem you're having.

[Zoinac]

Awsome, well, it sucks that everyting doesn't jsut work perfectly the frist try.. but eh whatever. if you watch the flash from the onboard flash, then immeadiatly after watch the flash from a stand alone unit, you can indeed notice the pre-flash... it's not really seperate, just noticable... Thanks for telling me about it, I would never have thought of that!

Now... just to save my pennies :D