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11-26-2014, 01:35 PM   #1
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High Speed Sync Flash question

I have a K30 and a Pentax flash capable of High Speed Sync flash. I noticed in the K30 manual, it said that the camera should be on M or Tv modes for HSS flash.

Is it true that it won't work with Av?

Thanks

11-26-2014, 01:52 PM   #2
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QuoteOriginally posted by Spodeworld Quote
Is it true that it won't work with Av?
Yes, that is true. You must be in a mode where you control the shutter speed. In HSS, flash output is constant for the duration of the exposure. As a result, depending on shutter speed, the guide number of the flash will change and the camera will adjust the aperture to suit. At least that is how I understand the process. In M mode you control the aperture with correct setting being determined by calculation and/or trial and error.


Steve

Last edited by stevebrot; 11-26-2014 at 02:04 PM.
11-26-2014, 02:17 PM   #3
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Well, with Av you don't get to set (force) the shutter speed to be faster than 1/180. You need to be in a mode that allows you to do that. I think M is best, unless you are happy for the camera to choose the wide open aperture. Even TAv, where you select both shutter speed and aperture, isn't ideal, since it will normally select a very high ISO (though you can override that by adjusting your auto ISO range on the Info screen). I'm referring to the K3 here, but I think the K30 is similar.
11-26-2014, 02:20 PM   #4
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I thought that one of the uses was for when you want to set a large aperture and use HSS for fill flash. Seems convenient that you could choose a large aperture in Av mode, and if the camera selects a high shutter speed of like 1/2000 or 1/4000, then HSS would be used. Based on what you're saying, you wouldn't have that convenience.

11-26-2014, 02:48 PM   #5
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Actually, that does work (on the K3 at least). I just tried it with my Metz 52 AF-1 in P-TTL HSS mode. However, slow speed sync is the usual approach to fill-in flash in bright light. I haven't compared the results from the two techniques.
11-30-2014, 11:08 PM   #6
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QuoteOriginally posted by Paul the Sunman Quote
Actually, that does work (on the K3 at least). I just tried it with my Metz 52 AF-1 in P-TTL HSS mode. However, slow speed sync is the usual approach to fill-in flash in bright light. I haven't compared the results from the two techniques.
I got my Sigma EF-610 DG Super to fire in HSS mode with the camera set to Av and the shutter forced above 180, but the exposure was totally wanky towards overexposure with that flash.

QuoteOriginally posted by Spodeworld Quote
I thought that one of the uses was for when you want to set a large aperture and use HSS for fill flash. Seems convenient that you could choose a large aperture in Av mode, and if the camera selects a high shutter speed of like 1/2000 or 1/4000, then HSS would be used. Based on what you're saying, you wouldn't have that convenience.
This question comes up frequently and is driven by the desire to use wide apertures in full sunlight for foreground isolation in addition to fill. Weddings are the classic example and the classic solution is a leaf-shutter lens with standard flash on a medium format body.

The K-3 manual is pretty explicit when it states, "Select an exposure mode (such as Tv) which allows you to set the shutter speed". The K-5IIs, K-30 and K-50 manuals simply say "Tv or M". That being said, it is possible to shoot in Tv mode at an arbitrarily high shutter speed in order to force a wide aperture. The program used for that case is that mandated by the flash guide number (varies with shutter speed) and there is still a bit of guess-work involved since the guide number can go quite low.

HSS is a flash feature that is gated by camera capabilities and with current Pentax bodies, seamless HSS in Av mode is not supported. Things are a bit different in Nikon and Canon land, but still not seamless. Here is a link with a pretty good (though dated) discussion of the technology:

http://www.scantips.com/lights/flashbasics2b.html

- and -

http://nikonclspracticalguide.blogspot.com/2008/03/10-auto-fp-high-speed-sync-explained.html


Steve

Last edited by stevebrot; 12-01-2014 at 12:04 AM.
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