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02-20-2012, 03:32 PM   #1
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50mm Manual Focus lens on Kx

I took some sample shots with my 50mm f/1.4,, 28mm &135mm lenses I've had for 30+ yrs. With all the lenses, I set the focal length per the LCD screen, shot in manual, hit the green button & the 50's shots were all blown out. Any suggestions?

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02-20-2012, 03:44 PM   #2
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Did you set the related custom function "Use Aperture Ring" to "Permitted"?
02-20-2012, 04:19 PM   #3
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Yes, Ole it's set to that--it's strange that the 28 & 135 both worked fine--I took all three shots right in a row, only adjusting the focal length per the LCD screen....
02-20-2012, 05:24 PM   #4
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You're probably shooting at too large of an aperture. Do you get the same results when shooting at F8?

It should also be noticed that stop-down metering has a tendency to be off by a constant factor- so in this case, try doing -1EV and see if you get better results. Whenever I use the K 15mm lens, I need to do the same (and as a consequence I never use it any more).


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02-20-2012, 06:28 PM   #5
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Two things: 1 - the 'green' button adjustments aren't always perfect. My k-x tends to overexpose about 1/3 of the time, so I sometimes need to hit the green button a few times.

That said, there are also a few variables to play with; is the green button set to change the shutter speed? what apertures are the lenses set to?
02-20-2012, 06:33 PM   #6
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QuoteOriginally posted by Adam Quote
so in this case, try doing -1EV and see if you get better results.
EV compensation isn't a function of M mode. AFAIK you have to tweak one of the shooting parameters yourself.

QuoteOriginally posted by ok2day Quote
I set the focal length per the LCD screen, shot in manual, hit the green button & the 50's shots were all blown out. Any suggestions?
Is it reliably stopping down to meter? If the diaphragm of the 50 is sticky, perhaps it isn't stopping down properly when you shoot, resulting in the camera metering for a smaller aperture than it ended up using. What aperture did you shoot at? Does it expose properly wide open?
02-20-2012, 06:41 PM   #7
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you used spot metering... what did you focus when you pushed the green button? You have to be careful with spot metering when shot being taken is with mixed light/dark areas.
02-20-2012, 06:52 PM   #8
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QuoteOriginally posted by Adam Quote
You're probably shooting at too large of an aperture. Do you get the same results when shooting at F8?

It should also be noticed that stop-down metering has a tendency to be off by a constant factor- so in this case, try doing -1EV and see if you get better results. Whenever I use the K 15mm lens, I need to do the same (and as a consequence I never use it any more).
Shot at f8, f1.4, f22--all blown out, all did change somewhat

02-20-2012, 07:01 PM   #9
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QuoteOriginally posted by Philoslothical Quote
EV compensation isn't a function of M mode. AFAIK you have to tweak one of the shooting parameters yourself.



Is it reliably stopping down to meter? If the diaphragm of the 50 is sticky, perhaps it isn't stopping down properly when you shoot, resulting in the camera metering for a smaller aperture than it ended up using. What aperture did you shoot at? Does it expose properly wide open?
Phil--I think you're on to something--that diaphragm might be the culprit--I shot it shown here at f8, I also shot at f22 & f1.4 & it was blown out.

How does one fix a stuck diaphragm--heck, the lens is over 30 yo & isn't worth sending in to fix

The other two lenses worked fine--I was somewhat surprised they were as sharp as the 2 shots posted.
02-20-2012, 07:04 PM   #10
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QuoteOriginally posted by minolta2pentax Quote
you used spot metering... what did you focus when you pushed the green button? You have to be careful with spot metering when shot being taken is with mixed light/dark areas.
min-I focused on the tree trunk, just like the other two that came out ok..
02-20-2012, 07:10 PM   #11
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Have you ever looked at your metering with the lenses. The metering with some lenses and specifically some cameras is really off. I plot all my lenses using a uniformly lit block wall and green button metering at each aperture click. Check out threads on the K10/20 and metering and you will see probably a chart I produced to show the issues pertaining to metering. I used a K50/1.4 for all my tests
02-20-2012, 08:24 PM   #12
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Unless I've missed something, you don't seem to mention which 50mm lens you have. If it has a auto/manual switch like a takumar, perhaps it's set to auto.
02-20-2012, 08:28 PM   #13
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If it is sticky blades a f1.4 50 should be worth saving and not too costly if you use Eric our favorite Pentax repair man.
02-20-2012, 08:42 PM   #14
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I've got the old M mount mate--nuthin' fancy...
02-20-2012, 09:58 PM   #15
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It would be worth trying again using center weighted metering, just to see what happens. Wide open, and maybe f/4 and f/8. When you have the aperture ring stopped down on the lens, and you manually move the aperture arm, is the diaphragm snappy when you let it go?
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