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Photography Question 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
 

Flash Sync


Now and again, I need to shoot in P, AV, or anything close to it, because of lighting conditions or whatever - the question is: do I sync my camera to 1/60s or 1/250, or can I o/ride this and not have a sync speed?


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5/15/2007 6:41:05 AM

 
Kerry L. Walker   Robyn, I have no idea what you are asking. LOL Please explain.


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5/15/2007 8:05:21 AM

 
W.   
Doesn't your cam sync itself automatically when you switch on the flashgun?

Whether you can override the sync speed depends on your camera and what kind of shutter it has. Centralized shutters are generally synced at all shutter speeds. Curtain shutter mechanisms have a top sync speed limit. Usually between 1/160th and 1/250th. If you use faster shutter speeds only part of the image will be lit.

What camera have you got, Robyn?

When using flash with LOWER shutter speeds the ambient light will be progressively more visible/important in the image.

Test it for yourself! Use fill-flash in daylight on a subject. Make a few exposures, each with a slower shutter speed than the last. SEE the difference with your own eyes. You've got digital, so it won't cost you a dime.

Have fun!


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5/15/2007 8:17:14 AM

 
Andy 
BetterPhoto Member Since: 5/28/2002
  Your 30D's max sync speed is 1/250 if you want your flash as main light source. Of course you can manually set it to slower, 1/125, 1/60, etc. If you use the dedicated EX Speedlite (580 II, 580, 550, 430 and 420), you can sync it to higher speed than 1/250 if you set your flash to High Speed Sync (the symbol H with the lightning next to it) and for fill light purposes. Hope this helps.


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5/15/2007 8:27:49 AM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Sorry Kerry :) Ok, got it in front of me, and it's the Custom Function (03)I'm looking at - I've 2 options - 0 - which is Auto or 1 - which is 1/250 (fixed)so this is my sync speed? - If I have it on Auto, it seems to be governed by my F stop, and 'Fixed' seems to be my sync speed of 1/250 as indicated by Andy If its at 1/250s, I can then select any F stop from 4 all the way up and my light is pretty much the same - does this then mean that the flash is pumping out more power/light, the higher the F stop? (Andy I'm using the 580EX) I've just played with the 'H" and seen what you mean - but why would I want it higher than 1/250th?( To really freeze motion?) Sorry if this is a bit rambly, but its how I talk!
So, if I leave it on 1/250s and shoot on Aperture, I'll have enough light - if I really want to push it higher, I can then set it to Shutter priority, and select the 'H' and over ride my sync speed? You cannot use 'H' in AV mode, it stays at 1/250.
I was also told by another wedding photographer that he always shoots on 2nd shutter curtain. If I set that, and select 'H', it then cancels the 2nd shutter >>> arrows, so does this mean that the flash overrides the camera settings. I've selected 2nd curtain in Custom Functions on the camera and the flash, but was not able to gleen anything from the manual about which overrides which - ie camera / over flash, or flash/overides camera.
Ok, now I'm sure this is as clear as mud to you all - but I think I know what my question was! LOL - sorry Kerry, but thanks all :)
Sorry, last one - WS, what did this mean? "Centralized shutters are generally synced at all shutter speeds" whats a centralised shutter?


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5/15/2007 10:25:49 AM

 
Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
gregorylagrange.org
  Fixed sync at 1/250, your flash will adjust output to match the f/stop you select. Ambient light will appear different in the photo. Go up to a high aperture(f/16), the flash will shoot off lots of light, the background will look darker.
High speed sync reduces ghosting on moving things. Flash freezes motion, but you can still get ghosting from ambient light. Especially from light colors, like white shoes worn for sports.
Flash with aperture mode, you have to select apertures that won't cause the shutter speed to go over the sync speed. Otherwise you'll have half a picture exposed for just ambient light, and the other half exposed with a combo of flash/ambient.
2nd curtain makes a flash fire right before the shutter closes, instead of right after it opens. Regular flash with motion, you get the clear flash image with the ghosting traveling ahead of the direction of motion. 2nd curtain makes the ghosting behind the clear flash image, like the speed lines behind the roadrunner in the cartoon. The timing of the flash in 2nd curtain sync is why it cancels when selecting high speed sync.
Slrs like yours have a shutter that opens by falling down, like when you release window blinds quickly. The shutter blades drop, then a curtain finishes the exposure by closing in the same up and down plane. The shutter is close to the film plane. View cameras and medium format have leaf shutters that open and close like the blades that open and close for the aperture. They're located near the point the lens makes the light converge on itself.


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5/15/2007 11:11:01 AM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Thanks Gregory. "Flash with aperture mode, you have to select apertures that won't cause the shutter speed to go over the sync speed" How would I get an F stop higher than /1250 (is that what you're saying), as that's my sync speed.
"The timing of the flash in 2nd curtain sync is why it cancels when selecting high speed sync." I understand 2nd curtain, but what do you mean by 'why it cancels' why, is the flash too fast? What does the 'H' push the flash up to? Sorry if I'm sounding dof - could be I am :) LOL


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5/15/2007 11:28:23 AM

 
Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
gregorylagrange.org
  If you're in aperture mode, and all apertures from f/8 to f/22 show that the correct shutter speeds are 1/250 or slower. If you want to combine flash with the ambient light, if you tried to use f/5.6, the correct shutter speed for that would be 1/500. That would be above the sync speed. Trying to use a flash with that is going to make a picture that has one part brighter than the other.
It's the same as a wrong sync speed inside a room that causes the black line across part of the picture.
The exact mechanisms of high speed sync I don't know, but it does have to do with the faster shutter speed and the timing of when the shutter opens and when the camera can fire off the flash with the faster shutter speed. Drawing out the time it happens to illustrate, say the normal flash sync process happens in one second. As soon as the shutter opens, between the .1-.4 mark the flash fires. Then at the .8 mark the 2nd curtain starts to close to finish the exposure.
A high speed sync takes that to the maximum so that there's no margin. Hence they say high speed sync only works with their dedicated flash.


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5/15/2007 12:08:38 PM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Ok, I've read it 4x now, and I think I know what you mean :) I'm going to bed, and will re-read it again tomorrow.I think I need to play with the camera, whilst I have this page open, sometimes it just makes the penny drop faster.
Thanks all


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5/15/2007 12:23:51 PM

 
Kerry L. Walker   Well, Robyn, I see that W and Gregory have pretty much answered your questions so all I can add are a couple of clarifications.

"Sorry, last one - WS, what did this mean? "Centralized shutters are generally synced at all shutter speeds" whats a centralised shutter?" He is talking about a leaf shutter. As Gregory pointed out, leaf shutters look and act like the aperture blades in your lens in that they open fully (to the f/stop selected) whenever you shoot. There is no travelling pair of curtains which may be fully open (at or below sync. speed) or one curtain following the other during the exposure this exposing only a small part of the film or sensor at a time.

High speed sync is only possible with a dedicated flash which supports this. With high speed sync the flash emits several short bursts as the curtains travel across the film (sensor) plane. The only problem is that the usable distance for the flash is very limited.


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5/15/2007 12:25:03 PM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Thanks Kerry - so high speed flash will really light up a fairly underlit subject, at a reasonably close distance, but won't spread much to surrounds?


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5/15/2007 12:40:27 PM

 
Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
gregorylagrange.org
  Now that I see the mechanisms, a high speed flash needs short distances because it wouldn't be able to shoot off too much power due to multiple burst of light.


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5/15/2007 12:49:03 PM

 
Kerry L. Walker   Bingo, Gregory.

Robyn, I think you are confusing Gregory's explanation of how a higher sync. speed (with the same aperture) will allow in less ambient light than a slower sync. speed. For example, 1/250 sec. at f/5.6 will let in less ambient light than 1/60 at f/5.6. In either case, unless you are metering for the ambient and the flash is only providing fill flash, the flash will properly light the subject. It will just provide more light at 1/250 than it will at 1/60.

High speed sync. just allows you to use a higher than normal sync. speed. I really wouldn't worry too much about this. I have it but never use it.


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5/15/2007 1:18:16 PM

 
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