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08-19-2008, 02:25 PM   #1
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50-135 issue?

ok, now I'm getting really confused with my 50-135... here's an example of what's going on all the time, at f/2,8...
in some shots, focus is just right, it's nice and sharp (maybe I over-sharpened it a bit), and in some shots it's really bad. Same body, same lens, about 1 hour between the shots..

anyone else had these simptoms? any ideas what to do? I did focusing tests, it all came out fine, overall I'm happy with it, but at 135mm and 2,8 - half is not so good



08-19-2008, 06:54 PM   #2
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If you are using the multi-AF point option, the lens may be getting confused. Try some quick snaps using only the centre AF point to see if that is the problem. My 50-135 has never given me this sort of random effect, but I have never used the multi-point AF option except as a try it out.
08-19-2008, 08:57 PM   #3
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Is anyone else the 999,999th visitor prize-winner on Imageshack? Or 10,000th on another ad? I must be lucky - won on 2 of 4 clicks.
08-20-2008, 03:56 AM   #4
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QuoteOriginally posted by Canada_Rockies Quote
If you are using the multi-AF point option, the lens may be getting confused. Try some quick snaps using only the centre AF point to see if that is the problem. My 50-135 has never given me this sort of random effect, but I have never used the multi-point AF option except as a try it out.
no, I have my AF points on selective, it just seems like AF sometimes does the job right, and sometimes shows some front/back focusing... at first, I thought it's only on extreme short distances, like 1-1,5m, but yesterday I noticed this.
really confused, I think I'll go see local pentax service center, I just don't like idea of waiting for repairs if needed

08-20-2008, 02:10 PM   #5
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Clearly the guy eating is not very sharp *at all*. Is that the whole picture, or a crop from something else? Was he (or you!) moving when you shot it? Could you post the EXIF?

But what are seeing wrong with the shot at right? At the size posted, it looks as sharp as could reasonably be expected of any zoom lens at its extreme for both focal length and aperture, although I suppose if you posted a 100% crop, I might feel otherwise.
08-20-2008, 02:25 PM   #6
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I've not had this with my copy of the 50-135, it is always sharp

However, recently I have had this problem with my Sigma 24-70 F2.8, which indicates a problem with the lens rather than the body. My Sigma is about to go back to Sigma to look at.
08-20-2008, 04:27 PM   #7
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QuoteOriginally posted by Marc Sabatella Quote
Clearly the guy eating is not very sharp *at all*. Is that the whole picture, or a crop from something else? Was he (or you!) moving when you shot it? Could you post the EXIF?

But what are seeing wrong with the shot at right? At the size posted, it looks as sharp as could reasonably be expected of any zoom lens at its extreme for both focal length and aperture, although I suppose if you posted a 100% crop, I might feel otherwise.
those are 100% crops, converted from raw... First shot, guy eating, he was sitting on the bench, I was sitting on the bench about 5-6m away. Second one: me standing, handheld shot, about 10m away, both are iso 100, f/2,8, 135mm.

today I made couple of shots, and only one was soft, and it wasn't too bad, I'd say it's about right for max. aparture and tele-end...
08-20-2008, 06:38 PM   #8
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QuoteOriginally posted by silent_eyes Quote
those are 100% crops, converted from raw... First shot, guy eating, he was sitting on the bench, I was sitting on the bench about 5-6m away
Would be useful to see the whole shot. Sure looks like the camera focused elsewhere. Not sure if that because it foudn soemthing else to focus on, or if it just missed (ie, FF/BF).

QuoteQuote:
Second one: me standing, handheld shot, about 10m away, both are iso 100, f/2,8, 135mm.
And like I said, for a lens at its extremes, that looks fine to me. Does it not to you?

08-21-2008, 12:32 PM   #9
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QuoteOriginally posted by Marc Sabatella Quote
Would be useful to see the whole shot. Sure looks like the camera focused elsewhere. Not sure if that because it foudn soemthing else to focus on, or if it just missed (ie, FF/BF).
ok, I'll post full-size, so let's check together

QuoteOriginally posted by Marc Sabatella Quote
And like I said, for a lens at its extremes, that looks fine to me. Does it not to you?
agreed, second one is most satisfying, that's the confusing issue in some shots, lens gives really great results, and in some, same body, same lens, same conditions, almoust horrible. Still, I belive it's more of user-based problem than lens, since it's clearly very capable of producing great shots. Let's say, problem appears in 2 out of 10-15 shots...
Tommorow I'll go out again, first I'll give it a bit of pet-talk, so we'll see
08-24-2008, 05:09 PM   #10
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ok, just to inform you guys - I found and fixed the problem! It turned out it was dirty focusing screen that caused all the problems... I washed it, and now lens is working just great... I think I'll buy a new focusing screen just to be on the safe side, since I guess I left some stuff on it again, it's almoust imposible to handle it right at home
08-24-2008, 07:46 PM   #11
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What a find! I would never, ever, have thought of cleaning the focusing screen to fix AF problems. Well done!
08-24-2008, 11:37 PM   #12
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Since when does the focising screen have anything to do with AF? (Your AF stuff typically sits under a second mirror under the main mirror, while the metering does seem to happen at the focus screen, AF does not)
Do you manually override what your AF system just found? o_O
Sure you don't just suffer from dirty lens contacts like jsherman did the other day? After cleaning his contacts his eradic behaving 50-135 behaved well again.
08-25-2008, 01:17 AM   #13
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QuoteOriginally posted by morfic Quote
Since when does the focising screen have anything to do with AF? (Your AF stuff typically sits under a second mirror under the main mirror, while the metering does seem to happen at the focus screen, AF does not)
Do you manually override what your AF system just found? o_O
Sure you don't just suffer from dirty lens contacts like jsherman did the other day? After cleaning his contacts his eradic behaving 50-135 behaved well again.
I actually first checked contacts, cleaned both lens and body, and it had no effect.

A friend who works for local pentax dealer and I talked and he mentioned that sometimes dirt can cause such wild focusing issues, if focusing screen is a bit messy or there's just a bit of dust near AF point. Couple of months ago I did remove my focusing screen for purpose of testing split-screens, I guess that's when I left some oil from fingers or dust on screen itself.
I'm not entirely sure that this was the problem itself, however - lens is working way better and in about 200 shots - I haven't noticed any focusing-errors. Since the only thing I did was cleaning focusing screen, it should be it, right?

I can't really belive that problem solved itself
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