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03-09-2010, 05:09 AM   #46
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QuoteOriginally posted by xxDavexx Quote
When using the lens in "red" or "green" modes, however, setting the aperture to the value marked on the chart resulted in severely underexposed photos. After some playing around, I realized that the K10D is attempting to set the flash exposure using the sensor on the flash, but apparently with the manual lens wide open. Even so, the amount of underexposure was about a full stop different between the "red" and the "green" mode. With the same subject about 1 meter away, I discovered through trial and error that I needed f stops of 5.6 and 4 for correct exposure. IOW, about 1/4 and 1/8 of full power.

The automatic "red" and "green" modes expose at roughly 1/2 and 1/4 power on an AF lens in Av mode. I presume this would also be true with M42 manual lenses as well. So the AF200S provides three power levels for all lenses on a K10D.
Forgive me if I say a "Yeah, I know that already" sort of thing here, but it sounds to me like you are misunderstanding how to read the aperture for the auto modes.

For the red and green settings there are a pair of red and green stripes alongside the distance scale. These indicate the distance ranges within which the flash can adjust output for the indicated aperture. The aperture you should use is indicated by the little square bit protruding from the stripes toward the distance scale. You don't read off the aperture by the same method you do for the manual (white) setting.

The sensor reads off reflected light from the subject and cuts off flash output when it senses enough light to give a correct exposure at the aperture indicated by the square. As the stripes cover quite a range of distances, quite naturally the power output varies according to the distance of your subject. It is NOT a set value of 1/2 or 1/4, though. For that to be the case, the correct aperture would have to vary according to the distance. The whole point of the auto modes is to free you from having to eyeball your distances on every shot.

The red setting covers a range between 1.4m and 7.1m. At ISO 100 you should use f2.8
The green setting covers between 0.6 to 3.5m. At ISO 100 you should use f5.6

As you can see, a set power level of 1/2 or 1/4 would not give the same exposure over such a wide range of distances. The sensor circuitry, with no interaction with the camera when the camera is in M mode, handles all the calculations for you. With an A series or later lens and the camera in an appropriate auto mode the flash and camera communicate and if all is working properly they will conspire to set your aperture for you automatically, even making the appropriate adjustment for changes in ISO settings.

This is all covered in the manual, and the only trial and error necessary is to perhaps make a slight adjustment for the vagaries of the possible differences between film ISO and digital ISO.

Again, the AF200S has only one manual power output level, and that is full blast (which is GN20m....not GN18).


Last edited by Mike Cash; 03-09-2010 at 05:23 AM.
03-09-2010, 03:55 PM   #47
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QuoteOriginally posted by rustynail925 Quote
Hi aleon what flash did you use in that picture?
Hi, Rustynail, I used my AF540 flash with Stofen diffuser.
03-09-2010, 07:56 PM   #48
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QuoteOriginally posted by aleonx3 Quote
Hi, Rustynail, I used my AF540 flash with Stofen diffuser.
Its a bit dim at the back isnt it? maybe its because of the diffuser?
03-09-2010, 08:34 PM   #49
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QuoteOriginally posted by rustynail925 Quote
Its a bit dim at the back isnt it? maybe its because of the diffuser?
Depends on what you want, however, it is never my intent to use flash to light up the background, this is the part where the ambient light takes over - a slightly dim background is by choice since I want the dancer with the white dress to stand out (and yet not over-exposed).

03-09-2010, 08:54 PM   #50
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Thanks for that sample pics. Is this in par with the Nikons SB600? or better?
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