what does highest sync speed mean

[mlipscomb]

When someone tell you to set your camera at highest sync speed, do the mean the shutter speed? Like 1/2000 ? Why is ISO sometimes refered to as ASA ?

[RandyMN]

The highest synch speed is that which your camera is capable of synching up with your flash. When I began photography it was rare to find an SLR that would synch up at greater than 1/60 of a second. Now cameras are capable of much higher shutter speeds.

Leaf shutters are capable of synching at all speeds while the type of shutter used in the SLR is a curtain shutter that must open and close like a curtain. If not synched properly then you will cut the image area in two pieces where the shutter was partilally opened.

ASA is just another standard for film speed. ISO is the one normally known while ASA I believe is the American Standrad Associated. You can do a quick Google to get that question answered better. I did a search and ASA (American Standards Association) and ISO (International Standards Organization) are basically the same thing

If you look at film you will see both ISO and ASA, but digital camera's use the ISO standard.

[friz]

Sync speed is the range of shutter speeds that you can use with flash. Above your highest sync speed you will only expose part of your sensor leaving a band underexposed. I think my rebel is 1/250 but I generally use 1/60 or 1/125 out of habit.

[jacuff]

Your shutter is made of two curtains. A front curtain and a rear curtain. The curtains move from the bottom to the top or top to bottom depending on the camera. (This way it only has to travel 24mm instead of 36mm if you want to think about it in terms of full frame or classic 35mm negatives.) The front curtain opens while the rear curtain closes. At speeds faster then the sync speed, the rear curtain starts to close before the front curtain completely opens. At speeds slower then the sync speed, the rear curtain is delayed before its starts to close.

So the sync speed of the camera is the speed it takes for the front curtain to open completely and then the rear curtain to immediately close.

[mlipscomb]

I wish there was a better way of thanking all the wonderful people who take time out of their day to answer my silly questions on the forum here....but I guess all I can really do it say thanks, I do really appreciate it.

[PhotosGuy]

The highest synch speed is that which your camera is capable of synching up with your flash. When I began photography it was rare to find an SLR that would synch up at greater than 1/60 of a second. Now cameras are capable of much higher shutter speeds. And sometimes you can squeeze out 1/400 if you need it for sports.
Test for yourself.
Strobe sync @ 1/400: Pushing the limits. (http://photography-on-the.net/forum/showthread.php?t=599450)

[Wilt]

Your shutter is made of two curtains. A front curtain and a rear curtain. The curtains move from the bottom to the top or top to bottom depending on the camera. (This way it only has to travel 24mm instead of 36mm if you want to think about it in terms of full frame or classic 35mm negatives.) The front curtain opens while the rear curtain closes. At speeds faster then the sync speed, the rear curtain starts to close before the front curtain completely opens. At speeds slower then the sync speed, the rear curtain is delayed before its starts to close.

So the sync speed of the camera is the speed it takes for the front curtain to open completely and then the rear curtain to immediately close.



..and when using the shutter faster than the sync speed, the opening between the two curtains forms a narrow slit. Since the flash is a very brief blast of light, it would expose that part of the sensor which is opened to the slit, so the rest of the sensor would not see the light output by the flash, leaving a black or dark section to the image.


ASA predates ISO; ASA and DIN were the American and European film speed ratings. They came together in the ISO standard to use one numerical value, and adopted the same numerical convention which had been used by the ASA.

[poloman]

A note that may be useful.
The sync speed does not affect your flash exposure, but does change the exposure of your background. If you want to brighten your background when using flash, dial in a slower shutter speed.