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10-01-2012, 02:35 PM   #1
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Pentax 15mm infinity focus

Hey guys,

I just got a DA 15mm F4 and I am really happy with it's overall sharpness, however it seems like the focus ring is inaccurate. Under autofocus things seem okay, however if I use manual focus, infinity focus is achieved before the actual infinity symbol (end of the rotation) and if you keep rolling you go past infinity and pictures end up all fuzzy. I searched the forum and I found at least two people who had the same issue. Is that an isolated problem or more of a design problem of all 15mm lens (sort of like the Rokinon 14mm problem). Thanks in advance!!

10-01-2012, 03:12 PM   #2
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All af lenses ive had is like that. I think they do this to let the af fine adjust or they dont care because the af does the job.
10-01-2012, 05:45 PM   #3
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Also, I believe it depends on the ambient temperature. Depending on that, true infinity focus may be just before, on, or just after the infinity mark.

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10-01-2012, 06:14 PM   #4
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I could understand that this might be vexing, but one of the nice features of the Limited series of lenses is the hyperfocal scale - you ought not be at the focus stop. Those little lines on the top of the lens barrel do more than decorate.

Play around with this. Online Depth of Field Calculator - this is a great tool for establishing "zone focus" for street shooting too

As for focusing past the infinity point.. I have an F 28mm 2.8 that annoyingly will not adjust past the infinity point, and as a result can on occassion not AF to infinity. It has its purpose.

10-01-2012, 06:21 PM   #5
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Thanks for the quick replies! What concerned me the most is that I am a bit of a perfectionist, so I was curious if it's a common issue with that lens. Just wondering if I should give another copy or try or just stick with this one. What do you think?
10-01-2012, 10:20 PM   #6
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It's not an issue. It's a design feature that infinity is not at the end - it aids in autofocus and allows for temperature variation. It,s normal and correct.
10-01-2012, 10:23 PM   #7
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Many lenses are designed that way to allow for contraction and expansion in different temperatures. Our lenses have to work in blazing heat and also the sub zero temps of winter. If it didn't go a little past infinity, it may not be able to focus to infinity on a hot day. Some telephotos can go quite a bit past infinity. I'm checking my DA 15 as I type. The line is about the center of the infinity symbol at the stop and at the 1 on the other end (0.18). Since it's 1:15 AM, I really can't check infinity focus to see where it stops with the auto focus. Since most of the time I shoot at f/8 or more with this lens, it really doesn't matter. I remember once in a "senior moment", I had left my camera set in MF after mounting the DA15 and fired off quite a few shots before I realized the lens was not focusing and at f/4. There is still so much DOF with this lens, almost every shot was still usable.
10-02-2012, 03:06 AM   #8
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I just checked DA 55-300, 18-55, 12-24, 10-17, 16-50 and 15 ltd. They all go past the mark, the 15 being closest to the center of infinity mark.

10-02-2012, 06:43 AM   #9
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Well, the problem is that my lens reaches infinity focus at the 1meter mark... I tried this with my 31mm ltd and infinity is right smack in the middle of the infinity mark. I think I am going to have to exchange the lens...

Last edited by oxidized; 10-02-2012 at 06:59 AM.
10-02-2012, 02:21 PM   #10
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QuoteOriginally posted by oxidized Quote
Well, the problem is that my lens reaches infinity focus at the 1meter mark... I tried this with my 31mm ltd and infinity is right smack in the middle of the infinity mark. I think I am going to have to exchange the lens...
Just tried the 15 in daylight. Manually focusing it to 1 meter causes infinity to be out of focus and objects close in sharp. Then auto focusing to infinity has the opposite effect. Send it back.
10-02-2012, 06:13 PM   #11
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Did today. Thanks again for the help Ex Finn.
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