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11-26-2009, 04:23 AM   #1
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Manual focus problem with K10D?

Hi all,

I love older fixed focal lenses and I have quite a few of those well made lenses. I love to shoot largest apertures around f1.2-f2. But I have found some problems when using those lenses on my K10D. I am not sure if my experience is unique or whether it is a specific problem with my K10D. Just to share my frustrations with you. Several people have mentioned the difficulty of using large aperture lenses at f1.2-f1.4. I could not find specific posts discussing the problem.

I bought a split screen (the jinfinance version) and the O-ME53 Magnifying eyepiece for my K10D. I have recently done some testing and found some very intriguing results.

When using the largest apertures, I can rarely focus precisely. The focus is either "left focused" or "right focused." In my tests, I usually rotate the focus ring about 1mm from the left to the right and shoot about 4-5 pictures. I normally repeat the same test 2-3 times. The results seem consistent with the same lens.

The following lens are "right focused." In other words, I have to rotate about one forth to a half millimeter from the visually perfect focuses to the right to achieve perfect focuses on the pictures : 1. Auto Mamiya/Seikor 55mm f1.4; 2. Auto Yashinon 50mm f1.4; 3. Auto Yashinon 50mm f2; 4. Vivitar 105 Macro;

Almost all the Pentax lenses I have tested or "left focused." In other words, I have to rotate about one quarter to one half millimeter to the left to achieve perfect focuses. The lenses I have tested so far are: SMCT 20mm f4.5 | ST 50mm f1.4 | ST 50mm f1.8.
Pentax M 28mm f2.8 | Pentax M 35mm f2 | Pentax M 50 f1.4 | Pentax A 50 f1.2


My Zeiss Jena 35mm Zebra f2.8 (a great lens) does seem to focus on target.

I could not test auto focus (AF) lenses since the focusing throw is too short.

Thanks for your insights.


Last edited by yyyzzz; 11-26-2009 at 09:08 AM. Reason: typos
11-26-2009, 07:38 AM   #2
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I noticed the same with my K10 with s/s and o-me53, except all my lenses needed a very slight twist to the left (only when shooting wide open mind you). I became aware right after installing the s/s - so it was easy to compensate for it.

c[_]
11-26-2009, 07:40 AM   #3
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I never have this issue with the standard screen so it must be that the SS is slightly off when a lens is wide open. A bit of a PITA since most focusing is done wide open.
11-26-2009, 09:04 AM   #4
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but not all lenses are the same

Thanks for the note.

But some of my M42 lenses are "right focused" for the lack of better terms. This is in contrast to most of my Pentax lenses almost of all which are left focused being either M42 or K mount.

11-26-2009, 09:41 AM   #5
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QuoteOriginally posted by yyyzzz Quote
Hi all,

I love older fixed focal lenses and I have quite a few of those well made lenses. I love to shoot largest apertures around f1.2-f2. But I have found some problems when using those lenses on my K10D. I am not sure if my experience is unique or whether it is a specific problem with my K10D. Just to share my frustrations with you. Several people have mentioned the difficulty of using large aperture lenses at f1.2-f1.4. I could not find specific posts discussing the problem.

I bought a split screen (the jinfinance version) and the O-ME53 Magnifying eyepiece for my K10D. I have recently done some testing and found some very intriguing results.

When using the largest apertures, I can rarely focus precisely. The focus is either "left focused" or "right focused." In my tests, I usually rotate the focus ring about 1mm from the left to the right and shoot about 4-5 pictures. I normally repeat the same test 2-3 times. The results seem consistent with the same lens.

The following lens are "right focused." In other words, I have to rotate about one forth to a half millimeter from the visually perfect focuses to the right to achieve perfect focuses on the pictures : 1. Auto Mamiya/Seikor 55mm f1.4; 2. Auto Yashinon 50mm f1.4; 3. Auto Yashinon 50mm f2; 4. Vivitar 105 Macro;

Almost all the Pentax lenses I have tested or "left focused." In other words, I have to rotate about one quarter to one half millimeter to the left to achieve perfect focuses. The lenses I have tested so far are: SMCT 20mm f4.5 | ST 50mm f1.4 | ST 50mm f1.8.
Pentax M 28mm f2.8 | Pentax M 35mm f2 | Pentax M 50 f1.4 | Pentax A 50 f1.2


My Zeiss Jena 35mm Zebra f2.8 (a great lens) does seem to focus on target.

I could not test auto focus (AF) lenses since the focusing throw is too short.

Thanks for your insights.
Why some lenses should be out one way and others out the other way I haven't got a clue. But I do know that the Katzeye fitted to my K10D did not give an accurate indication of manual focusing. The result was always slightly backfocused. Didn't matter stopped down, but it did matter wide open in low-light situations. Whether it was the screen or the camera I still don't know. That camera tended to back-focus on auto anyway (cured with the debug pirate software), but of course AF is a different system. I think there must have been a mild quality control issue with the assembly of the camera.
11-27-2009, 01:13 AM   #6
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the funny thing is that...

The focus tramp (the red focusing dots) also seems to mislead a little bit. It is a bit frustrating with my f1.2 lens. I always suspected that some of my manual lenses were defect in some ways...

QuoteOriginally posted by timo Quote
Why some lenses should be out one way and others out the other way I haven't got a clue. But I do know that the Katzeye fitted to my K10D did not give an accurate indication of manual focusing. The result was always slightly backfocused. Didn't matter stopped down, but it did matter wide open in low-light situations. Whether it was the screen or the camera I still don't know. That camera tended to back-focus on auto anyway (cured with the debug pirate software), but of course AF is a different system. I think there must have been a mild quality control issue with the assembly of the camera.
11-27-2009, 02:28 AM   #7
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This might be a stupid question, but does all of the lenses' focus rings turn to same direction to reach infinity? This might explain why some focus to "right" and some to "left".
11-27-2009, 02:42 AM   #8
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Ok, I googled some lenses and Vivitar Macro and Yashinon lenses indeed seem focus to different direction than Pentax so now I'm thinking you just have the the split screen a little bit too near or (far from) the lens.

Edit: Did you test all the lenses to the same target at same conditions? Why the Zeiss Jena would be spot on I cant explain.

When I had a jinfinance screen in my K100D I ajdusted the split screen position with thin strips of clear adhesive tape to act as a shim. It was a trial and error type adjustment but it didn't take too long.


Last edited by ovim; 11-27-2009 at 02:46 AM. Reason: added aquestion
12-01-2009, 05:50 AM   #9
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correct!!!!

I forgot this important point in time of frustration. Indeed, they have different focusing directions. That explains everything. Thanks a lot.
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