Rebel XT flash question.

[John_05]

the Rebel XT has a setting for 2nd curtain flash, but when i use it for long exposures the flash fires both when the shutter opens and closes. is there a way to set it so it only fires before the shutter closes, and not when it first opens?

 

[Cuervo79]

that;s what the second cortain flash option is for it shoots a 2nd flash just before the shutter closes, just turn off the option and it will only flash at the begining.

 

[rmh159]

that;s what the second cortain flash option is for it shoots a 2nd flash just before the shutter closes, just turn off the option and it will only flash at the begining.

The question was how to get the flash to fire only as it closes and not when it opens.

I'm not sure what the answer is to be honest... my D50 does the same on Rear Sync. I'm taking an educated guess here but I believe the first flash is a low powered flash intended to expose the background and then the last flash is high powered intended to expose the subject. Can anyone verify? I'm also not sure how to turn that first one off.

 

[Big Mike]

My first reply to this one was lost.

I don't think that you can turn off the first flash...but it doesn't affect the exposure.

The reason that it does this...is because of the E-TTL flash metering. The camera fires a pre-flash before the shutter opens...and uses that to determine the flash power required for the actual exposure.

This is really only a problem when you are shooting people with a longer shutter speed....which would increase the time between flashes. The first flash may cause them to blink or even to think that the photo has been taken...and look away. If the shutter speed is faster, both flashes fire rather quickly.

 

[John_05]

My first reply to this one was lost.

I don't think that you can turn off the first flash...but it doesn't affect the exposure.

The reason that it does this...is because of the E-TTL flash metering. The camera fires a pre-flash before the shutter opens...and uses that to determine the flash power required for the actual exposure.

This is really only a problem when you are shooting people with a longer shutter speed....which would increase the time between flashes. The first flash may cause them to blink or even to think that the photo has been taken...and look away. If the shutter speed is faster, both flashes fire rather quickly.

thanks for the help Big Mike. ive been too busy to try the shot im thinking of, but now that i know the first flash wont effect the exposure, ill have a go at it tonight. if it works out like im envisioning it, ill post it here.

if it doesnt, and its not an extremely embarassing shot, maybe ill post it in the blooper section. :lmao:

 

[w.pasman]

The camera fires a pre-flash before the shutter opens...and uses that to determine the flash power required for the actual exposure.

Maybe you can link the flash power to the focus distance? That would solve your double flash problem without creating bloopers

 

[Big Mike]

Maybe you can link the flash power to the focus distance? That would solve your double flash problem without creating bloopers

Actually, I think the camera does actually use the focused distance (when using Canon lenses) to help determine the exposure...but I don't think that we can do it because I don't think that the flash power can be manual set on this camera. We can set the FEC (flash exposure compensation) but that is still based on the E-TTL metering.

If you had a manual flash unit...then yes, you certainly could calculate the flash power with the distance and the units Guide Number.

 

[RickyN29]

Yes, it is firing in order to determine flash exposure. I do not know of any way around it. And yes, it causes subjects to move thinking you already took the pic. If this is the case, just announce 'Wait for second flash'