What is Flash synchronisation?


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Wallace

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#1
What is that term, does it mean the metering (exposure values) took into consideration the additional light provided by the flash...?

How do I make use of it?

Thanks.
 

ckiang

Senior Member
#2
Simply means the synchronisation of the flash's firing and the shutter being full open on cameras. You don't have to do anything to use it, other than setting it to the flash sync speed or below, as dictated by the manual. On SLR-type cameras, setting a shutter speed above flash sync speed results in half-exposed pictures as the shutter will not be fully open when the flash fires.

Regards
CK
 

mpenza

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Jan 18, 2002
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#3
for non-slr type cameras, you could sync at almost any speed. some cameras could sync at 1/1000s (approximately the actual flash duration).
 

ckiang

Senior Member
#4
Originally posted by mpenza
for non-slr type cameras, you could sync at almost any speed. some cameras could sync at 1/1000s (approximately the actual flash duration).
Flash duration can actually be shorter than 1/1000s. :D Basically focal plane shutter cameras (most SLRs and some rangefinders like the Leicas and Voigtlanders) have a lower flash sync speed (~1/50 to 1/250s). Cameras with in-lens shutters can sync even at beyond 1/1000s. :)

My avatar water drop is shot at 1/500s with flash. :)

Regards
CK
 

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Wallace

Guest
#5
Actually, I am pretty confused over the relationship between metering and flash.

Will the exposure values as given by the light meter change when I have a external flash unit on the hot shoe, compared to when I am not using a flash unit, for the same scene with identical light conditions?

I mean, with more light given off by the flash unit, surely the shutter speed will be faster or the aperture smaller, to compensate for the 'extra' light? Will the light meter take into consideration the 'extra' light given off by the flash?

Thanks, I hope my questions make sense...
 

#6
Originally posted by Wallace
Actually, I am pretty confused over the relationship between metering and flash.

Will the exposure values as given by the light meter change when I have a external flash unit on the hot shoe, compared to when I am not using a flash unit, for the same scene with identical light conditions?

I mean, with more light given off by the flash unit, surely the shutter speed will be faster or the aperture smaller, to compensate for the 'extra' light? Will the light meter take into consideration the 'extra' light given off by the flash?

Thanks, I hope my questions make sense...
Shutter speed does not affect flash exposure. Only aperture affects flash exposure.

Normal "dumb" (read : Manual) systems will not take ambient light into account. You set the aperture based on subject distance and flash guide number. The closer you are to the subject and the higher the guide number for a given ISO, the smaller your aperture has to be.

The camera light meter does not take into account the additional light given off by the flash. It only reads ambient light exposure. You, or the camera + flash system has to take care of it. Note that under dark/dim conditions, your camera light meter will always register underexposure. This is okay, as long as you are within flash's range, your exposure will be correct if you set the correct aperture (if you are using manual flash). If you are using TTL, this should not be a problem.

Manually calculating a good balance between flash and ambient exposure is going to be a pain. Most cameras nowadays have advanced TTL flash exposure systems which does this balancing for you.

Regards
CK
 

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