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Old Apr 2, 2008, 12:44 AM   #1
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Join Date: Apr 2008
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I have a flash hooked into my camera (Pentax K100D Super) using a hot-shoe to PC adapter, The camera only activates the flash at 1/160th shutter speed (on full manual)not higher, not lower. the flashes are 1/1000th, anyone have any advice? I'd like to speed up my shutter, that was the whole point of getting the slave flashes.
The flashes have no settings on them, very basic. What's the deal?! HELP!

Is there any way to override the sync?
I went through the flash thread and didnt find anything helpful there...
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Old Apr 2, 2008, 12:12 PM   #2
Join Date: Jun 2003
Location: Savannah, GA (USA)
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I don't know why it wouldn't be firing at a slower shutter speed.

But, if you don't want part of your frame dark, you'll need to stick with the x-sync speed or slower if you're not using a dedicated Pentax Flash with P-TTL High Speed Sync (a.k.a., FP mode) available.

That's because you have a travelling slit of light at shutter speeds faster than the sync speed, because both shutter curtains are never fully open at the same time.

So, a flash has to be designed to pulse the light as this slit moves across the frame. Otherwise, you'd get a partially exposed frame when using a single flash burst (since only part of the frame would be exposed by the shutter curtains at speeds faster than the x-sync speed).

The flash burst duration on a typical flash is around 1/1000 second or faster. Because it's so short, and because of the the way shutter curtains on a camera have to be designed to support faster shutter speeds (resulting in a moving slit of light), you have to pulse the light over the duration of the exposure using a flash with that ability (a dedicated flash that supports high speed sync).

But, unless you're shooting outdoors at wider apertures, you probably don't need to use anything faster than the x-sync speed anyway. That's because if you're shooting a lower ISO speeds in a typical indoor environment, your subject is only going to be properly exposed during the flash burst duration (frame would be dark if the flash was not being used). So, the fast flash burst (typicall 1/1000 second or faster) then freezes the action.

Only when you have a lot of ambient light in the image (for example, if using higher ISO speeds and wider apertures indoor), will you have problems with motion blur from subject movement. Otherwise (stick to lower ISO speeds indoors), the flash itself can usually freeze the action in dimmer surroundings with a 1/160 second x-sync speed (since the subject is only exposed properly during the very short flash burst).

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