Rear curtain sync - DPChallenge Forums

Sony 16-50mm f/3.5-5.6 E-mount

01/13/2003 02:38:46 PM · #1

Something that's been bothering me for a week or so now. Why would a photographer ever _not_ use rear-curtain sync ? On longer exposures with flash it gives a more natural 'streak' before the subject, rather than afterwards.

Yet, front-curtain sync always seems to be the default - any reason ?

jmsetzler

Sony Alpha a6000

01/13/2003 02:41:29 PM · #2

If you are on a tripod all the time, rear curtain sync would work fine as the default...

Sony 16-50mm f/3.5-5.6 E-mount

01/13/2003 02:44:17 PM · #3

Originally posted by jmsetzler:

If you are on a tripod all the time, rear curtain sync would work fine as the default...

Why would the tripod make a difference ? I'm trying to understand when it would make sense to actually use front-curtain sync, yet it always seems to be the default.

Message edited by author 2003-01-13 14:48:56.

jmsetzler

Sony Alpha a6000

01/13/2003 02:50:02 PM · #4

Originally posted by Gordon:

Originally posted by jmsetzler:
If you are on a tripod all the time, rear curtain sync would work fine as the default...

Why would the tripod make a difference ?

I believe that the most common use of the flash is two fold... 1 - to illuminate your subject and 2- to freeze motion. I agree that the rear curtain sync is popular for freezing a motion trail at the end of the exposure, but it is not the most common application of the flash.

99% of photographers are doing snapshots. In low light situations where flashes are required, they don't want blur.

Since the larger numbers of 'photographers' are not pursuing art, I think the default of front curtain sync is in place for these reasons?

Just my thoughts as to why...

Sony 16-50mm f/3.5-5.6 E-mount

01/13/2003 03:09:16 PM · #5

Originally posted by jmsetzler:

Originally posted by Gordon:
Originally posted by jmsetzler:
If you are on a tripod all the time, rear curtain sync would work fine as the default...

Why would the tripod make a difference ?

I believe that the most common use of the flash is two fold... 1 - to illuminate your subject and 2- to freeze motion. I agree that the rear curtain sync is popular for freezing a motion trail at the end of the exposure, but it is not the most common application of the flash.

99% of photographers are doing snapshots. In low light situations where flashes are required, they don't want blur.

Since the larger numbers of 'photographers' are not pursuing art, I think the default of front curtain sync is in place for these reasons?

Just my thoughts as to why...

That is more a question of the shutter speed though, and not the flash synchronisation, isn't it ?

You can after all do rear-curtain sync on a 1/60s exposure and not notice any difference at all between that and a front-curtain sync. I just can't get my head around why you'd want to do front-curtain sync ever really - unless you were actually going for some sort of odd effect.

jmsetzler

Sony Alpha a6000

01/13/2003 03:19:50 PM · #6

Dunno, but i think i can possibly find an answer... :)

SharQ

Canon EOS-30D

Canon EF 28-135mm f/3.5-5.6 IS USM

01/19/2003 06:54:02 PM · #7

Originally posted by Gordon:

Yet, front-curtain sync always seems to be the default - any reason ?

The reason is more historical than anything else;

When SLR cameras first came on the market, the max shutter speeds were not very impressive. I have one laying around somewhere that cannot cope with anything faster than 1/200. The problem, of course, is that the flash can only go off in a fraction of that; Only when the shutter is COMPLETELY open (not on its way to being open or on its way to being closed) can the flash be fired.

historically, this was accomplished by syncing the flash at 1/30 (later, 1/60 sec became the norm), because this meant that the shutter (either through closing and opening the aperture leaves, or by having a little curtain) would come to a standstill. Firing the flash happened mechanically (i.e an electric connection was passed through the camera and back up to the flash, which would create a spark, and the gunpowder (flashpowder, really, but it amounts to the same thing) would light the subject.

When people started using better, electronic flashes, the sync speed remained at around 1/60 - only quite recently was a flash sync of around 1/125 sec normal in consumer cameras.

When the sync was changed from mechanical (electrical) to electronic, the software in the camera could start controlling the flash. This meant that we finally got an option as to when we would want to fire the flash. Naturally, a rear-curtain flash is more natural (to freeze the motion at the end of the movement), but this was unusual, because of the camera traditions.

Why cameras still offer the choice

So, it is part traditional why first-curtain flash is the norm. There is, however, another very good reason for why you would want to use first curtain.

When digital cameras were new, there was massive outcry about this horrible thing called shutter lag - the lag between pressing the button and the picture actually being taken. Only in newer DSLR cameras (and more expensive compact digicams) is this shutter lag on the level with even simple film SLR cameras.

This translates to flash sync as well. Imagine using a 1/60 shutter time, and then using last curtain flash. In practice, this means that the time from you press the shutter until the flash fires is 1/60 of a second. Doesn't sound to bad, but if you pressed the shutter at THE critical moment, that 1/60 can make or break your camera.

In other words; If you want to take the picture when you press the button, use first curtain flash. If you want the flash to look as natural as possible, use end curtain flash.

Fast Sync

There are, of course, high-speed flash units such as the combination of D60 / EX550, which can sync at 1/4000 second. Interestingly enough, I believe that most of Canons' cameras switch to first curtain sync regardless of the Custom Function setting, if the shutter speed exceeds 250 (which is the "standard" x-sync speed). Of course, this is largely irrelevant; When you go to speeds over 1/250 (i.e 1/500, which is the first step above 1/250, if I am not mistaken), the difference in time between first and last curtain is less than 1/500 second, in which case you are unlikely to be bothered by first / last curtain sync.