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08-31-2007, 03:50 AM   #1
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AF assist via external flash?

Does the Pentax K10 use any info from the 540 flash to help to focus the lens in poorly lit situations??

Some of the competition uses the flash AE light as a AF assist light. Does the Pentax??

I was shooting in a dark aquarium, and had to use the built in flash on the weakly illuminated tanks. There was a significant delay in focussing, and shutter release. I wonder if an external flash would have helped both in flash cycle time, and AF.

In spite of the flash reflection, I was able to get some good images, but the AF times were very slow.

Please advise.

Martin

08-31-2007, 05:13 AM   #2
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YES! Get the 540! It has a mode where it will fire it's IR focus-assist beam but NOT the flash. I've used this feature when I am going non-flash with my 50mm f/1.4 (folks go "hey, the flash didn't fire!") Of course, if you are using the flash as "flash" , the IR beam will aid in AF as well. Don't think my old Sigma EF-500 Super had this AF-assist/no-flash mode.

Oh, regarding the "info from 540 flash", I believe the K10D just sends a "it's dark, fire the IR beam" message to the flash, and that's it. The beam will hopefully "light up" the subject enough for the AF to work. BTW, I've used this in complete darkness and it works! And the picture actually comes out decent. Did I say you need to buy the 540

Yeah, the "flash-pulse-of-death-as-AF-assist" is kinda awful if you ask me. Unfortunately, when I use the built-in flash to trigger my 540 wirelessly, it uses the built-in for AF assist, rather than the off-camera 540 Time to get another 540 or some hotshoe cables.
08-31-2007, 05:26 AM   #3
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QuoteOriginally posted by egordon99 Quote
Don't think my old Sigma EF-500 Super had this AF-assist/no-flash mode.
You're correct, it does not. It *will* do AF-assist with its "IR" beam, but will always flash during exposure.
08-31-2007, 07:38 AM   #4
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QuoteOriginally posted by egordon99 Quote
YES! Get the 540! It has a mode where it will fire it's IR focus-assist beam but NOT the flash.
The Pentax AF-360FGZ also has this feature. The flash project a fairly dim pattern of red lines (not infra-red) that will assist the camera's AF system. There is a switch on the back of the flash to select this mode. The red lines are not irritating to human subjects, unlike the AF assist flashes from the built-in flash.

It is NOT an active AF system as found in some P&S cameras. Also, the AF assist pattern is used only when the camera determines that it needs it. In my experience, the AF assist pattern often will not fire even when it would be useful to speed up focus. The only time it will fire consistently is in near total darkness. Because the pattern often doesn't fire when needed, this feature has not been very useful for me. YMMV.

09-02-2007, 01:41 PM   #5
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The Sigma EF-500 Super can shine its assist light and not fire the flash if it's set to the ISO adjust mode. It;s probably a bug, but it works.
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