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08-24-2009, 04:01 PM   #1
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k10d flash and shutter speed question

I am sorry if this is a dumb question.

In manual mode, I set the shutter speed to 1/350 and apperture to 5.6. Now when I pop up the flash, the shutter speed goes down to 1/180 What should I do to keep the shutter speed unchanged and at the same time to fire the flash.

Thanks

Mouli.

08-24-2009, 04:18 PM   #2
Ash
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No silly questions, only silly answers

Flash sync speed is 1/180 - this is the fastest shutter speed that will allow the flash to completely register in the shot. You need it faster, then you have to go to high-sync-speed flash mode and set your Tv accordingly. But as a result of that, you'll find the flash intensity needing to be boosted to compensate for the faster shutter speed, risking maxing out the flash and not having as much reach.

Hope that helps.
08-24-2009, 04:54 PM   #3
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Do you mean to say I need to use flash units like Pentax AF 360?
08-24-2009, 05:06 PM   #4
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Ooh yes, I forgot to mention that.
HSS is only available with P-TTL capable external flash guns (not just the Pentax-branded ones).

02-24-2010, 12:56 PM   #5
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QuoteOriginally posted by Ash Quote
No silly questions, only silly answers

Flash sync speed is 1/180 - this is the fastest shutter speed that will allow the flash to completely register in the shot. You need it faster, then you have to go to high-sync-speed flash mode and set your Tv accordingly. But as a result of that, you'll find the flash intensity needing to be boosted to compensate for the faster shutter speed, risking maxing out the flash and not having as much reach.

Hope that helps.
For anyone interested, you also must customize OFF the Auto EV compensation

Rui
02-24-2010, 01:14 PM   #6
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QuoteOriginally posted by vsmouli Quote
Do you mean to say I need to use flash units like Pentax AF 360?
Yes (or other P-TTL HSS capable flashes)
02-24-2010, 01:36 PM   #7
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Keep in mind that HSS may not be as useful as regular, 1/180 flash, for stopping action.

Because the shutter is not fully open at speeds faster than 1/180, the flash must fire multiple times during the exposure. It almost turns the flash into a continuous light source. At 1/180, the flash duration, which may be as long as 1/1000 or as short as 1/50,000 second, controls the exposure and action stopping power. In HSS mode, the shutter speed is the controlling factor.

There was a thread a while back about this. Someone posted shots of an electric fan taken with normal and HSS. The normal flash (1/180) froze the fan blades perfectly, as one would expect. The flash duration was very short. Above thatshutter speed, the fan blades were completely obscured by motion blur. The shutter speed of 1/250 or 1/500 wasn't fast enough to stop the action.

High speed flash is most useful when the ambient light is bright enough to result in a good exposure of the subject, in spite of the flash. By speeding up the shutter speed, you can eliminate the effect of the ambient light, leaving only the flash exposure. If the ambient light is very low, such that at 1/180, the image would be more than two or three stops underexposed, then the flash takes over and hss is not necessary.
02-24-2010, 02:55 PM   #8
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Right - if you're setting shutter speed to 1/350" because you think you need that to stop action, that's not true with flash. the actual duration of the flash is much shorter than that. You could set shutter speed to 1/60" and not see any difference in motion-stopping ability.

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