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07-21-2009, 05:06 AM   #1
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P-TTL and Sync Speed

I have a K100d and I wanted to know how the shutter curtain worked (vertical or horizontal). I've been reading a bit about how you can use faster shutter speeds than your camera's sync speed if you don't mind some shadow in the frame where the training (leading?) curtain covers the flash area.

I attached my AF 540FGZ to see if it worked any better (manual mode 1/4 power). If I used manual or Tv mode on the camera, the camera took pictures at 1/4000 sec - they looked OK, but I found that the flash reset to P-TTL mode. How does this work? How am I able to take a visible picture at 1/4000 when the K100d is supposed to have a sync speed of just 1/180?

Thank you in advance!

07-21-2009, 06:23 AM   #2
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The flash must have been using high-speed sync mode where it "strobes" throughout the exposure to make sure the frame is completely exposed. This only works at reduced power so the flash can fire repeatedly without discharging completely.

07-22-2009, 08:18 AM   #3
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K10D Shutter

The K100D shutter is a vertical travel type. The max synch speed is 1/180 second. That is, the shutter is completely open only at speeds of 1/180 or slower. Faster than that and the trailing curtain begins closing before the leading curtain is fully open, resulting in a moving slit that travels across the sensor. A normal flash, used at speeds faster than 1/180 second, would only expose part of the sensor. The faster the shutter, the smaller the area exposed.

Some P-TTL flashes (not all) are capable of High-Speed-Synch (HSS). In this mode, the flash fires several times as the shutter traverses the sensor. This reduces the amount of light considerably. The AF540-FGZ is one of the flashes that is capable of this.

I don't believe that the onboard flash is capable of HSS, even though it is a P-TTL flash.
07-22-2009, 12:52 PM   #4
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Original Poster
Thank you both! That does make sense. I should review my flash manual again .

I bought the flash on sale before the price jump for a particular set of applications, and since I don't know much about flash photography I didn't delve too deep in the manual.

It will be a fun tool to experiment with. Now I just need to get it off camera...


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