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12-21-2013, 03:22 PM   #1
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AF200FG flash question(s)

1) When using the AF200FG flash, if it's set to "Auto" does that mean it's pretty much going to fire regardless of what the internal settings of camera is?

2) Do changing any settings of the camera change the way it flashes, or are those settings for the cameras built in flash ?

3) I turned one of the AF200FG flash to another option besides "Auto" and it completely over-exposed - explain that please.

12-21-2013, 04:29 PM   #2
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1) Auto, at least on this particular flash, means P-TTL mode. The camera controls the flash power, judging the scene with a little preflash, then firing at whatever power is needed to properly expose based on your aperture and ISO.

2) The settings in the camera will have the same effect with that flash as with the internal flash.

3) Full means full power, it will flash the same every time, so you must compensate with aperture and ISO based on your subject distance. the -1 and -.5 are exposure compensation for auto mode, they will underexpose by 1 or 1/2 stop.

Last edited by elliott; 12-21-2013 at 04:35 PM. Reason: Fixed 3, was thinking of the wrong flash.
12-21-2013, 04:32 PM   #3
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PENTAX AF200FG Flash - Review - PentaxForums.com
reviews this flash and its functions
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12-22-2013, 03:43 AM   #4
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Just some flash basics.

The power of the flash is expressed in its guide number. For the AF200, it's 20 meters (@ISO100). The subject distance can be calculated using

subject distance equals guide number divided by aperture (1)

and the aperture can be calculated using

aperture equals guide number divided by subject distance (2)

In manual mode on the AF200 (full), this means that if your subject is at 5 meters, you have to select 20/5 equals aperture f/4 for correct exposure. Anything in front of that (closer to the camera) will be overexposed (the closer to the camera, the worse) and anything further away from the subject will be underexposed (the further away, the darker).

The guide number increases (with the square root of 2) when you increate the ISO; so at ISO200, the guide number is 28 and at ISO400 it will be 40.

Formula (1) also applies when using TTL / pTTL (auto on the AF200); but in that case it's the maximum subject distance that can be correctly exposed. If the subject is closer, the camera will adjust the flash duration to achieve correct exposure at the given subjet distance. You will still have overexposure of anything closer and underexposure for anything further away.

There is now also a minimum subject distance (due to a minimum flash duration); check the tables in the user manual. A subject closer than this will always be overexposed.

If you don't have the manual, you can download it from Operation Manuals Download : Support & Service | RICOH IMAGING

Note: stay away from auto-iso when using flash; the camera might well decide to use maximum allowed ISO (e.g. 1600) often resulting in overexposure in TTL / pTTL mode due to minimum flash distance.

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