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02-26-2012, 09:55 PM   #1
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Explanation Needed

On my K-5 with the DFA 100mm WR macro attached, when the flash is popped up and ready, the time shown is 1/180 sec. With the same camera and my
new DFA 50 mm macro, the time is 1/100 sec. This seems counter-intuitive since the 50mm is closer to the subject for the same frame as the 100mm. Is there
something I'm not setting in the menu or ??? Yes, same f stop in my tests. It is probably a simple explanation.

02-26-2012, 09:59 PM   #2
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Sounds like the camera might be choosing different exposure settings as the FOV of the 50mm is wider (and in your case more it was probably picking up more dark areas). Another possibility could be that the flash wasn't ready when you looked through the VF, so the shutter speed w/o flash was shown.

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02-26-2012, 10:37 PM   #3
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In two days of shooting with the new 50 mm it is always 1/100 and two yrs. with the 100, 1/180. You are probably correct on the FOV theory. When very closeup, it forces you into a high
fstop so you don't white out. Most the time I use a Manfrotto gear head tripod for the tight shots and don't use flash. Thanks.
02-26-2012, 10:38 PM - 1 Like   #4
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What mode are you shooting in. In Av mode shutter speed is chosen to minimise camera shake, hence slower for shorter lenses.

02-27-2012, 01:29 AM   #5
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twitch is probably right.
I usually shoot macro in M mode... Only that way I can be sure what settings are used.
02-27-2012, 04:10 AM   #6
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Below my experience (quoted from https://www.pentaxforums.com/forums/pentax-dslr-discussion/170163-k-x-flash-s...ml#post1762672)

QuoteOriginally posted by sterretje Quote
On a side note:
In Av mode, the camera sets a shutter speed (in my experience) for flash that is partially based on the focal length used. In a dark scene, the K100D in combination with DA55-300 uses roughly 1/FL (1/60 @55mm, 1/125 @ 100mm, 1/180s @ 150mm). In a brighter scene the same combo uses 1/180s regardless of focal length, possibly attempting 'fill-in flash'.

K5 with FA31Ltd or DFA100WR is more conservative and uses 1 / (2 * FL) in a dark scene; not tested in a bright scene.
02-27-2012, 05:21 AM   #7
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QuoteOriginally posted by john mood Quote
On my K-5 with the DFA 100mm WR macro attached, when the flash is popped up and ready, the time shown is 1/180 sec. With the same camera and my
new DFA 50 mm macro, the time is 1/100 sec. This seems counter-intuitive since the 50mm is closer to the subject for the same frame as the 100mm. Is there
something I'm not setting in the menu or ??? Yes, same f stop in my tests. It is probably a simple explanation.
I suppose you shoot P-TTL? First, one should note that the shutter speed itself tells little about how much light the sensor receives as the flash duration is much shorter than the shutter speed and the output power of the flash is varying too.

The only way to ensure a fixed shutter speed will be in Tv, TAv or M mode. In Av mode the shutter speed may indeed vary dependent upon focal length as stated in the K-5 manual (p. 182). In P- and Sv mode the camera will really have to guess what your intent with blurr, background illumination etc. might be.
02-27-2012, 09:47 AM   #8
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Great info. Thanks. I always shoot in AV mode (P-TTL), but checked other modes. In TV and TAV, the sync changes to 1/125. I'll check the k-5 manual (p.182) which I missed.
I am not a sophisticated shooter and hardly use the many capabilities of the K-5. But a fellow can still enjoy driving a Ferrari, even though his name is not Fangio.

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