430EX Query

topcatproduction

topcatproduction

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Hi, I recently bought a 430EX for my 40D which is my first ETTL flash gun, and not sure if I'm using it quite right! When I press the button on the flash gun to change it to rear curtain sync, it flashes once at the beginning of the shot and once at the end, I was expecting just once at the end as an oppose to once at the beginning as with the default setting? Hard to tell but the first flash doesn't seem quite so bright but not a lot in it.

Any ideas?!
 
if the flashgun is on TTL, the first flash just before the shutter opens lets it guess the exposure, and then it fires properly just before the shutter closes.

if on first-curtain sync, the flashgun just has to give one flash that is used for guessing and lighting up at the same time.
 
willsphots said:
if the flashgun is on TTL, the first flash just before the shutter opens lets it guess the exposure, and then it fires properly just before the shutter closes.

if on first-curtain sync, the flashgun just has to give one flash that is used for guessing and lighting up at the same time.
Click to expand...

Indeed this, confused the hell out of me at first! Also does it with the onboard flash. A good 'What are you doing you stupid camera... oh' moment.
 
willsphots said:
if on first-curtain sync, the flashgun just has to give one flash that is used for guessing and lighting up at the same time.
Click to expand...

Not strictly true, the single flash is probably two flashes, just so close together they seem as one.

Matt
 
MatBin said:
Not strictly true, the single flash is probably two flashes, just so close together they seem as one.

Matt
Click to expand...

For the ETTL to work it does indeed fire a 'pre' flash and this enables it to then work out what it should be outputting to get a correct exposure. it happens so fast that for normal shots you never see it, but with rear curtain sync you of course have the metering flash to start with then the actual flash just before the shutter closes.

You are indeed doing everything right and please take some confidence in that.
 
You were all right- the first flash does not show up. Can someone explain about the high speed setting though? All I can see is that it lets the camera shoot faster than 1/250 but not sure how it gets over the problem which normally limits it (black line across pic when I have tried faster with a manual flash)??
 
topcatproduction said:
You were all right- the first flash does not show up. Can someone explain about the high speed setting though? All I can see is that it lets the camera shoot faster than 1/250 but not sure how it gets over the problem which normally limits it (black line across pic when I have tried faster with a manual flash)??
Click to expand...

My guess is a longer flash burst.

With a manual flash, the shutter has to be fully open when the flash fires. At higher shutter speeds, the rear curtain starts to close before the first curtain is fully open, which means that when the flash fires part of the image doesn't receive any light.

With high speed sync, I'm guessing the flash fires as the first curtain starts to open, and shuts off once the rear curtain has closed.
 
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