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01-08-2020, 04:03 PM   #1
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Older manual K mount lenses and infinity focus

I seem to have problems getting my old non-A, ancient Pentax lenses to focus to infinity on the K-01. They just don't seem to reach it, at least an SMC 28mm Pentax 3.5 and a 50mm Pentax 2.0. Both work fine on other bodies. And more modern lenses work on the K-01. Just incompatible?

01-08-2020, 04:44 PM   #2
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I can't speak authoritatively about older lenses on the K-01. I will say, though, I've encountered a number of vintage lenses with hard infinity stops, in various mounts, that are less-than-perfectly adjusted for infinity focus when paired with a DSLR or mirrorless platform. In the days of film, I guess this wasn't so apparent because no-one was viewing images at the same reproduction ratios we use during processing and editing.

In some cases - especially where the focus ring incorporates a pin or stop to limit further rotation - these lenses can be adjusted by loosening the focus ring, turning it a little and re-tightening. But it varies on a lens to lens basis...
01-08-2020, 04:55 PM   #3
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I've used MUCH older (uncoated M42) lenses, as well as SMC and M lenses on my K-01s. I don't think I have an SMC 28/3.5, but I do have both the Takumar and SMC versions of the 35/3.5 and all the various M 50s, and I never noticed problems with focusing to infinity.
01-08-2020, 05:01 PM   #4
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I've run into this with M42 lenses. I've got a couple I've been meaning to tear down to see if I can adjust.

01-08-2020, 05:06 PM - 1 Like   #5
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Define "infinity"...

Many vintage lenses were adjusted at the factory to an arbitrary standard based on focal length (e.g. 2000x or similar). Such works fine with optical viewfinders,* but not so well when using 1:1 magnification in digital live view. Most lenses allow for adjustment of infinity focus and with some it is as easy as shifting the focus dial a few degrees. On others, some disassembly may be required.


Steve

* Consider degrees of arc for a 28mm lens along with average visual acuity and very quickly, 60m and the horizon start to look pretty much the same in the viewfinder, even for a sensitive split-image focus aide. Several of my 28mm lenses dial in at about that distance.
01-08-2020, 05:21 PM   #6
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QuoteOriginally posted by stevebrot Quote
Define "infinity"...

Many vintage lenses were adjusted at the factory to an arbitrary standard based on focal length (e.g. 2000x or similar). Such works fine with optical viewfinders,* but not so well when using 1:1 magnification in digital live view. Most lenses allow for adjustment of infinity focus and with some it is as easy as shifting the focus dial a few degrees. On others, some disassembly may be required.


Steve

* Consider degrees of arc for a 28mm lens along with average visual acuity and very quickly, 60m and the horizon start to look pretty much the same in the viewfinder, even for a sensitive split-image focus aide. Several of my 28mm lenses dial in at about that distance.
I have a wonderful Orion-15 6/28 lens in Soviet rangefinder M39 mount. Many copies of it are reported as being unable to achieve "infinity" focus on adapted mirrorless platforms, and it isn't easily adjustable without shaving down the hard stop pins inside. Mine is exactly the same. I thought about shaving the pins, but for the sake of originality, I just live with it. The result is, distant detail isn't quite as defined as it otherwise could be, especially when viewing images at 1:1 reproduction on my displays. At some point, I'll shave an L39 adapter specifically for that lens...
01-08-2020, 05:42 PM - 1 Like   #7
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QuoteOriginally posted by BigMackCam Quote
At some point, I'll shave an L39 adapter specifically for that lens...
I was actually having that thought as I was reading your post. You might even be able to do it by hand using a piece of plate glass and some emery cloth and a little finesse.
01-09-2020, 10:30 AM   #8
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I have the same 28mm 3.5 lens I picked up a few years ago to use with K-5. After awhile I realized I wasn’t getting infinity. There was an adjust I did using some guidance posted in another thread on this forum .....wasn’t difficult and seemed to improve it. I can’t recall the exact steps offhand, but it involved removing the outer ring and repositions the focus stop.

I think this was the thread:

Pentax M 28mm 3.5 Infinity Focus Issue - PentaxForums.com

01-10-2020, 02:43 PM   #9
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I use many (3 dozen?) pre-AF lenses, and I've never had a discrepancy with infinity focus between (or among) bodies. IOW, if the lens makes it to infinity on one body, it makes it to infinity on all.
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