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09-30-2010, 10:26 PM   #31
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Hmmmmmm




10-01-2010, 06:39 AM   #32
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QuoteOriginally posted by crossover37 Quote
Here is the response I got from the Pentax supervisor. He experiences the same issue with his FA 50mm F1.4 so I guess it's just the lens and how it reacts at f1.4

Jon,
Looking at your 2 RAWs, I can see that you are not doing anything
wrong, and the camera does not look like it is doing anything funky
either.

I tested a different model camera(K20D) and a different ISO set (560
vs 2200) with my FA 50mm f1.4 and got similar results as you. This to
me proves that it is a lens specific issue, not a camera or setting
specific issue.

I also tested some other very fast lens and noticed that at their most
wide open aperture setting there was some under-exposure as well.

The lens also vignettes more at f1.4, which is a common result when
shooting at or near wide open apertures, that usually disappears
completely by stopping down 2 stops. This of course makes the photo
look even darker.

I would say that your lens is not defective, but this is just the
result of the design of the lens, and the way light interacts at wide
open apertures. Replacing or repairing the lens would not give you a
different result.

Essentially, your best solution is just to be aware that if you shoot
wide open you may have to compensate a half stop.

I know this is probably not what you were hoping to hear, but I
believe it to be the correct answer.

That said, if you have doubts, you are always welcome to send the lens
into our shop, where they can test it for issues.
sounds a lot like my answer
10-01-2010, 09:27 AM   #33
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Yes thanks Lowell. I wanted to see if someone tested the same lens with their camera to see if it happened with them too
10-01-2010, 09:40 AM   #34
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I wonder if replacing the focus screen with an L series from *ist models would resolve this issue? Is it possible that the incorrect results with my M lenses with the original screen caused by the stock screen actually roll over into the very fast lenses? Do you have anyone nearby who has replaced the stock screen with an *ist screen and could do the exposure tests to see if it is an unknown side effect of the new brighter screens?

10-01-2010, 10:10 AM   #35
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QuoteOriginally posted by Canada_Rockies Quote
I wonder if replacing the focus screen with an L series from *ist models would resolve this issue? Is it possible that the incorrect results with my M lenses with the original screen caused by the stock screen actually roll over into the very fast lenses? Do you have anyone nearby who has replaced the stock screen with an *ist screen and could do the exposure tests to see if it is an unknown side effect of the new brighter screens?
I don't think it is related because the test shot was manual settings, simply trading shutter speed for aperture setting.

the only thing I wonder about, since it implies the FA 50/1.4 is only truely a 1.7 is how my old SMC 50/1.4 or super tak 50/1.4 compare in manual mode.

I asked the OP to try it also using the apereture ring.
10-01-2010, 10:13 AM   #36
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QuoteOriginally posted by Lowell Goudge Quote
I don't think it is related because the test shot was manual settings, simply trading shutter speed for aperture setting.

the only thing I wonder about, since it implies the FA 50/1.4 is only truely a 1.7 is how my old SMC 50/1.4 or super tak 50/1.4 compare in manual mode.

I asked the OP to try it also using the apereture ring.
Oops. I goofed that one - I was thinking metering rather than physical stop down. I don't have a lens that fast, so I cannot play with the exposure settings. My fastest lens is a S-M-C Takumar 55/1.8.
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