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08-31-2009, 06:46 AM   #1
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M42 Lens Caution

Dear Pentaxians, read the virtues of M42 lenses so much on this forum, that I ended up buying two from San Mateo California.
a) $10 Auto Yashinon-DX 50mm f1.7 from a camera shop - lens in excellent condition almost mint ; b) $10 Mitakon Wide MC 28mm f2.8 from a Russian Pawn Shop - like new.
I had the original Pentax Adapter and immediately mounted the Yashinon on my K20D. Tack sharp and brilliant TRUE colors that I never achieved with the AL II 18-55 Kit Lens.
Then tried the Mitakon. Again TRUE colors with sharpness matching the kit lens.
The next day tried the Yashinon again this tine at INFINITY focus. Alas the viewfinder blanked out after I got a shot. I reasoned that the mirror must have got stuck on the lens barrel in its return stroke as I had noticed that the rear barrel travel was much greater than the auto aperture pin length. The moment I moved the lens out of Infinity I got back the view in the finder. Thanks God.
Question: 1) How many Pentaxians have faced this problem.
2) What do I do to correct this situation.
I am cautioning all M42 fans to be wary of a potential problem - mirror fouling the lens.
Good Luck

08-31-2009, 07:49 AM   #2
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I've had many M42 lenses of different brands and never had this problem on my K100D or K200D. Some Googling revealed that it's a known problem with some Yashinon lenses.

In this thread on Manual Focus Forum there's even a quote from some old Yashica body manual:

"Because of the special construction of the mirror, the following Yashinon interchangeable lenses cannot be mounted on the yashica Electro AX:
Yashinon-DX 21mm f/3.3
Auto Yashinon-DX 28mm f/2.8
Auto Yashinon-DX 50mm f/2, f/1.7, f/1.4"

Apparently the "special construction of the mirror" is common in many other cameras including your K20D and the mirror was somewhat different in earlier Yashica bodies for which these lenses were originally meant for
08-31-2009, 07:50 AM   #3
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hmm! I did not know that there could be a mirror hitting issue with APS-C cams!

One workaround that is known to work for Canon 5D MkII is to shoot in Live View mode (since the mirror will be up).



First, set the focus to anywhere not near infinity.

Go into Live View mode. Do all your shots in Live View, including your infinity shots.

Put the focus away from infinity.

Go out of Live View.


Let me know if that works (would be good to know!)
08-31-2009, 08:22 AM   #4
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so this is more of a Yashinon warning than an m42 warning since this is an extremely isolated incident. ( I have never heard of any m42 lens hitting the mirror of an APS-C body) you will find that most people here use Takumars, but the vast majority that use 3rd party lenses have no problem at all.

08-31-2009, 08:07 PM   #5
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Even my auto Rikenon K-mount does not have this issue on my K20D.
08-31-2009, 08:29 PM   #6
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This is indeed strange since the mirror for APS-C is much shorter than any M-42 camera I am aware of. The mirror issue with the DX Yashinons is well-documented for film bodies and I guess we now know this to be an issue for Pentax dSLR bodies as well!

Steve
08-31-2009, 10:38 PM   #7
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Well, I can tell you that none of my M42 lenses in San Mateo, California have that problem!

I don't think it's the location.
09-01-2009, 12:41 AM   #8
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QuoteOriginally posted by Quicksand Quote
Well, I can tell you that none of my M42 lenses in San Mateo, California have that problem!

I don't think it's the location.


09-01-2009, 01:18 AM   #9
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QuoteOriginally posted by Quicksand Quote
Well, I can tell you that none of my M42 lenses in San Mateo, California have that problem!

I don't think it's the location.
What about the one you sold?
09-01-2009, 01:40 AM   #10
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QuoteOriginally posted by RawheaD Quote
hmm! I did not know that there could be a mirror hitting issue with APS-C cams!

One workaround that is known to work for Canon 5D MkII is to shoot in Live View mode (since the mirror will be up).



First, set the focus to anywhere not near infinity.

Go into Live View mode. Do all your shots in Live View, including your infinity shots.

Put the focus away from infinity.

Go out of Live View.


Let me know if that works (would be good to know!)
I'm afraid I don't understand how using Live View would prevent the mirror from hitting on infinity shots. I don't believe the camera shoots directly from the Live View mode, but rather drops the mirror, then raises it again for the shot. Correct me if I'm wrong. My camera is in my truck or I'd do an experiment and check it for myself.
09-01-2009, 06:04 AM   #11
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QuoteOriginally posted by Mike Cash Quote
I'm afraid I don't understand how using Live View would prevent the mirror from hitting on infinity shots. I don't believe the camera shoots directly from the Live View mode, but rather drops the mirror, then raises it again for the shot. Correct me if I'm wrong. My camera is in my truck or I'd do an experiment and check it for myself.
I just tried this with my GX20. The mirror definately does drop down and then raises again to take the photo. This does seem rather inefficient and causes quite a delay between pressing the stutter button and actually taking the photo. Mabe this can be fixed in the firmware though (any chance Pentax / Samsung ? ). Working in live view is probably not the solution to this problem. Maby the only solution is to save that lens for close up and macro work with a reverse mount or extension tubes.
09-01-2009, 09:04 AM   #12
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I am a little confused, but I will ask a few questions

I can't find any reference to yashica lenses (yashinon) with M42 mounts, all I see are bayonet

however,

when you are focused to a distant object, is the lens at infinity, or is there still travel?

If there is still travel, then the registration distance for the body this lens was designed for is further away from the focusing plane, and you may be able to solve the entire issue by using a flanged adaptor,

I am surprised that the lens can go up, but does not return, since one would expect both up and down to be impacted. Are you sure the mirror is not returning?
09-01-2009, 09:14 AM   #13
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Possibly the aperture pin on the back of the lens is the problem.
09-01-2009, 10:56 AM   #14
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QuoteOriginally posted by Lowell Goudge Quote

...I can't find any reference to yashica lenses (yashinon) with M42 mounts, all I see are bayonet...
Try this Google search:
yashinon dx - Google Search
I am pretty sure that all of the M42 Yashica lenses were Yashinons. Many lenses in the DX series had a very deep rear element. I think that the cameras were designed with a special articulated mirror design. I was aware of problems with various film SLRs and some Canon FF digital, but this is the first I had heard of the mirror not clearing on a dSLR.

Steve
09-02-2009, 11:08 AM   #15
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Mirror Fouling M42 Lens

Hello Steve and Ovim and all my Pentaxian Friends, I did some deep research on the net and came up with these facts:-
a) The Auto Yashinon-DX 50mm f1.7 did foul the mirror on the Spotmatic SLR as reported by an old timer in one of the manual lens forums. This is because the Yashinon's have a wider rear lens barrel diameter and they travel far out at infinity - much beyond the auto aperture pin.
b) Another guy says he took a dremmel tool and shaved of some metal from the top and bottom of the rear lens barrel. He solved the mirror fouling problem.
So taking a cue, here is what I did: a) Screwed open the rear lens retaining ring and removed the lens. b) Fitted a thermocole plug wrapped in thin plastic sheet to avoid debris falling inside the barrel, in place of the lens. c) Kept a fine emery sheet flat on a table and rubbed the rear lens barrel gently rotating the barrel with each stroke, d) Repeated this with the threaded lens retaining ring just a wee bit, e) Cleaned up every thing including the lens, f) Painted the rubbed ends with a permanent black marker, g) Fitted back the lens and its retaining ring.
Hey presto the mirror fouling problem disappeared. I think the mirror was just nicking the lens barrel which explains why it was getting stuck on the return stroke. Probably had I tightened the lens in the mount adapter – an original Pentax Japan – a little more, it would have fouled in the upward stroke itself. Note: this lens never centered on the top like my Practica camera with a Pentacon lens, rather it stalled at the 3 o clock position on the K20D body – hard to change and read f-stops.
Thanks to all my Pentaxian friends.
I would say please be cautious when mounting manual lenses, screw or bayonet, on your expensive DSLRs - manual lenses are cheaper than a DSLR my friends. Nanhi. Was in San Mateo California where I bought the two M42 lenses, now in Bangalore India.
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