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08-28-2013, 01:02 AM   #1
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M42 ST 50mm f/1.4 8 element

I have a K5II, original Pentax screw-mount adapter and a Super Takumar 50mm f/ 1.4 (8 element).

I read somewhere (maybe here) that someone was using a Canon and the mirror struck the rear element of the lens and I wanted to make sure these items are compatible before I try them.

When looking at pictures of the two lenses together, it appears to me that the rear element of the 8 design doesn't extend any farther back then the flange around the 7 element design. But I don't want to take any chances with the K5II.

If there is there anyone who actually has used this combination, I would appreciate it a response.

AP

08-28-2013, 01:21 AM   #2
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QuoteOriginally posted by Alaska Pentaxian Quote
...someone was using a Canon and the mirror struck the rear element of the lens...

I will point out that this is an issue specific to Canon cameras not Pentax cameras. There aren't any issues with this camera/lens combination because the K mount has exactly the same flange focal distance as the 42mm screw mount did. Canon DSLR cameras have a shorter flange distance* and this causes mirrors to scrape on lenses designed for longer flange focal distances. I have used the Takumar 50mm f/1.4 8 element version on my K10D without issue.



*Flange focal distance - the distance between the rear element and the sensor when the lens is focused at infinity - on Canon EOS cameras this distance is = 44mm. Pentax uses 45.46mm
08-28-2013, 01:21 AM   #3
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QuoteOriginally posted by Alaska Pentaxian Quote
I have a K5II, original Pentax screw-mount adapter and a Super Takumar 50mm f/ 1.4 (8 element).

I read somewhere (maybe here) that someone was using a Canon and the mirror struck the rear element of the lens and I wanted to make sure these items are compatible before I try them.

When looking at pictures of the two lenses together, it appears to me that the rear element of the 8 design doesn't extend any farther back then the flange around the 7 element design. But I don't want to take any chances with the K5II.

If there is there anyone who actually has used this combination, I would appreciate it a response.

AP
Hello!
I think it will only cause trouble for the "full frame" machines, because of the large mirror.
Here's a Canon 5D M42 Compatibility list:
Compatibility list of M42 lenses on Canon EOS 5D dslr
08-28-2013, 01:23 AM   #4
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No problems at all on Pentax bodies, the mirror is just really far forward in those Canons.

08-28-2013, 01:24 AM   #5
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M42 f1.4.8element50mm on to K5

Hi, You are very lucky the 8element f1.4/M42mount/50mm was the intended 'Planar'beater, beleived to have been hand built and Pentax apparently lost money on each one, and it was superceded by the 7 element version after a year, okay it's manual focus, okay it's slower in operation than 'today's' lenses but the quality is superb, especially around f8. The rear element does protrude farther 'back' and therefore should not be used on un-modified 35mm film cameras. However digital cameras have smaller mirrors and it should n't hit the rear of the lens. I have been using the M42 f1.4/8element/50mm on K5's and K20D's for over a year now with safe and excellent results. (incidentally comparison with the 1.8/55mm/7 element a highly rated (by Geoffey Crawley) Pentax lens shows the 8elementf1.4/M42/50mm to be marginally 'better' and definitly sharper).
Roger Gilroy
08-28-2013, 01:29 AM   #6
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QuoteOriginally posted by pater Quote
I think it will only cause trouble for the "full frame" machines, because of the large mirror.
Whether the camera is full frame or not is irrelevant - if the lens mount flange is shorter than the one the lens is designed for, unfortunate lens/mirror interactions are inevitable....unless you alter the geometry of the mirror or optical construction of the lens itself.
08-28-2013, 12:33 PM   #7
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If it is a problem, I don't know what it is, I have an 8 element supertak 50 and have used it for years on my K10 and *istD. If it is hitting the mirror, I have not seen it yet
08-28-2013, 01:21 PM   #8
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I have a manual for one of the Spotmatics which refers to this issue.

I think that it was an isue for ne or more of the Pentax SLR bodies which pre-dated the lens but that afterwards it was part of the design spec for the body to not have a problem.

08-28-2013, 04:00 PM   #9
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QuoteOriginally posted by Digitalis Quote
There aren't any issues with this camera/lens combination because the K mount has exactly the same flange focal distance as the 42mm screw mount did. Canon DSLR cameras have a shorter flange distance* and this causes mirrors to scrape on lenses designed for longer flange focal distances.
While OP should be fine with their setup, it's not just a question of flange distance.
The mirror of my Spotmatic would get scraped by a certain M42 lens when it was focused near infinity.
08-28-2013, 06:26 PM   #10
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QuoteOriginally posted by lytrytyr Quote
The mirror of my Spotmatic would get scraped by a certain M42 lens when it was focused near infinity.
Those lenses were focusing past infinity - this would bring the rear element closer to the sensor than was needed which would cause the mirror to impact the rear element.
08-28-2013, 06:58 PM   #11
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QuoteOriginally posted by Digitalis Quote
Those lenses were focusing past infinity - this would bring the rear element closer to the sensor than was needed which would cause the mirror to impact the rear element.
No, there was a hard stop at infinity.
The German lens wasn't matched to the Spotmatic's mirror trajectory.
08-29-2013, 12:51 AM   #12
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QuoteOriginally posted by lytrytyr Quote
No, there was a hard stop at infinity.
Of course there was a hard stop at infinity - that is how M42 lenses were designed to work. However a maladjusted lens, or one intended to work with a different camera can sometimes focus past that point and run into trouble with the mirror.
08-29-2013, 01:44 AM   #13
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Pentax M42/f1.4/50mm/8/7 element version.

290813 Hi Pentax users,reference above lens:
Hefty1 May 10 2010 says:The rear element on this lens protrudes when set on infinity(unlike the later 7element designs)and Asahi had to modify the cameras of the day to avoid this being fouled by the iris pin actuator.Modified cameras have an orange 'R' onthe rewind knob, non- modified models a green 'R' , so exercise caution before fitting it to an appropriate body or it'll all end in tears. quote ends.
So is this correct?
I use a 7/6 f1.4 on 35mm film and 8/6 f1.4 on digital. when f1.4 needed: me's very very happy with both.,
Regards Roger Gilroy.
08-29-2013, 05:21 AM   #14
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QuoteOriginally posted by Roger Gilroy Quote
290813 Hi Pentax users,reference above lens:
Hefty1 May 10 2010 says:The rear element on this lens protrudes when set on infinity(unlike the later 7element designs)and Asahi had to modify the cameras of the day to avoid this being fouled by the iris pin actuator.Modified cameras have an orange 'R' onthe rewind knob, non- modified models a green 'R' , so exercise caution before fitting it to an appropriate body or it'll all end in tears. quote ends.
So is this correct?
I use a 7/6 f1.4 on 35mm film and 8/6 f1.4 on digital. when f1.4 needed: me's very very happy with both.,
Regards Roger Gilroy.
I believe the cameras that post are referring to are the Asahi Pentax and Pentax S. The Pentax K was the first Pentax camera to feature semi-automatic or automatic aperture with Auto-Takumar or Super-Takumar lenses.
08-29-2013, 09:07 PM   #15
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QuoteOriginally posted by Digitalis Quote
if the lens mount flange is shorter than the one the lens is designed for, unfortunate lens/mirror interactions are inevitable
If the lens is properly adapted, the rear element of an M-42 or K-mount lens on Canon FF dSLR is the same distance from the focal plane as on a native M42 or K-mount SLR. The issue when adapted to the Canon is the mirror length and trajectory. There were similar cross-compatibility issues both within (Pentax SV green R, for example) and between brands back-in-the-day. A lens review would often contain a statement regarding mirror clearance on various target bodies.


Steve
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