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06-03-2010, 08:19 AM   #16
axl
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Location: Nove Zamky, Slovakia
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QuoteOriginally posted by olenl Quote
You are right.

My mistake was that I judged by my impressions with old 135 mm lens. Since I happened to have pointed it to the lighter areas, it received more light than wide kit lens, thus it was "faster". I have just checked with relatively the same light and those fixed lenses give similar shutter with the same aperture.

Another problem is that k-x's expometer seem to be way off with those lenses, I always have to either lower or raise the exposition (more often, raise) to get correct exposure. I also can't make flash work right with them but it's offtopic.
I don't know about K-x but with K10/20 and older bodies it was focusing screen that was to blame to have offset the exposure. With K-7 this was somewhat fixed and it's exposures with manual lenses are better than previous bodies but still not as good as with *istD and older (film). There was a member who had a go on *istD's focusing screen and fitted it into his K10D. The exposures were practically correct on any given f stop.

As it is now (at least with K10/20) correct exposure is obtained between f2.8 and f4... at anything faster than f4 my camera underexposes, and on f stops smaller than 5.6 it overexposes.... The margin of error increases the further from optimal f stop I move.... I assume your K-x may be the same....
As far as the flash goes, it will always fire at full power since there isn't any body/lens communication. You can calculate the f stop for correct exposure by finding out the Guide Number of your flash and eyeballing the distance to subject

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