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6 Days Ago - 3 Likes   #1
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Takumar m42 500mm F4.5 lens adventure

This is just an update into my Tukamar m42 500mm F4.5 lens adventure:
Well, I finally got it up and working! It took persistence and some face time with Fred at Universal Photographic in Kalamazoo, MI. He sat down with me and explained the theory behind the focus mechanism and from there it was just commitment. For this particular lens you want to have the helical splines engage in order to have the shortest overall length to enable focus past infinity. I had discovered the "person" who previously worked on this lens had engaged the helical two splines off that prevented focusing past Infinity. Once that is done it's just a matter of reassembling and focusing at infinity (the moon for me) and noting the amount of rotation from the hard stop and then making that adjustment. For me I was able to add a k-mount adapter (the one WITH the flange) from GOBE and still have plenty of room to focus past infinity by about an 1/8" looking at the markings. (the GOBE adapter stays with the lens and mounts like a regular K-mount lens - nice) I am not going to set the hard stop until I use it enough to know that's where it should be with both my bodys and teleconverter. So there you have it. One final word. If you add an adapter to your old screw mount and cannot focus to infinity there is adjustment that can be made to the stop and worse case you have to dig down to the helicals and change the engagement.

6 Days Ago   #2
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QuoteOriginally posted by Toolmaker Quote
For this particular lens you want to have the helical splines engage in order to have the shortest overall length to enable focus past infinity.
I'm curious how you determine this without simple trial and error.
6 Days Ago   #3
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I assume you mean the focal length part? Fred helped me realise that with this type of lens the longer the distance from the lens group to the sensor the closer it will focus and inversely the lens group needs to be at a specific distance to focus to infinity. From there when I disassembled the focus helical mechanism I could figure out that I could move the point of engagement to get it to the shortest OA length. This focus system only rotates 360 degrees minus the width of the stop so by allowing it to focus a bit past infinity I am losing some of the closer focus range. Considering the age of this lens I am sure they had some leeway on the assembly process at the factory and was able to make it up through adjusting the hard stop and then the scale position. I worked a bit a Eaton transmission for a while so I have some insight on gears and splines and such stuff so the mechanics are something i could work out.
6 Days Ago   #4
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Interesting info. One day I would like to get one of those to play with. Now you need to start posting some pics taken with it.

6 Days Ago   #5
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QuoteOriginally posted by Toolmaker Quote
This is just an update into my Tukamar m42 500mm F4.5 lens adventure:
Well, I finally got it up and working! It took persistence and some face time with Fred at Universal Photographic in Kalamazoo, MI. He sat down with me and explained the theory behind the focus mechanism and from there it was just commitment. For this particular lens you want to have the helical splines engage in order to have the shortest overall length to enable focus past infinity. I had discovered the "person" who previously worked on this lens had engaged the helical two splines off that prevented focusing past Infinity. Once that is done it's just a matter of reassembling and focusing at infinity (the moon for me) and noting the amount of rotation from the hard stop and then making that adjustment. For me I was able to add a k-mount adapter (the one WITH the flange) from GOBE and still have plenty of room to focus past infinity by about an 1/8" looking at the markings. (the GOBE adapter stays with the lens and mounts like a regular K-mount lens - nice) I am not going to set the hard stop until I use it enough to know that's where it should be with both my bodys and teleconverter. So there you have it. One final word. If you add an adapter to your old screw mount and cannot focus to infinity there is adjustment that can be made to the stop and worse case you have to dig down to the helicals and change the engagement.
Nice description of how the system works, I have the older 500mm with the rack and pinion focusing, however I have spotted a slightly fungus affected one like yours and I think I will give it a try
Thank you
6 Days Ago   #6
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It's an interesting beast of a lens. I had to fully strip my copy down to clean fungus out of it (success!). The focus mechanism is fun to reassemble the way it extends in both directions from the piece you actually rotate. Did you pick up on the tail piece being threaded inside so you can screw in a 49mm filter?
6 Days Ago   #7
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Wow that looks an impressive lens. Glad you have it sorted - would be great to see some photos shot with it!
5 Days Ago   #8
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Well, damn.

I have the K version. It's really a pretty good lens.


Here's the OP's original post: Takumar 500mm F4.5 lens repair - PentaxForums.com

3 Days Ago   #9
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I guess I am confused. The original M42 adapter doesn't have a flange and if you use the original adapter there should be no issue of infinity focus as long as the lens is correct in function. Someone fiddled with it and now you fixed the fiddling. There shouldn't be an adjustment needed to use it with an M42 adapter on a K-mount body if you have the correct adapter.
2 Days Ago - 1 Like   #10
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I didn't want the original Pentax adapter. That one was designed to stay with the camera so you could interchange screw mount lenses. I purposely wanted the flange type so I could leave it on the lens and still have it use the bayonet function.
2 Days Ago   #11
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QuoteOriginally posted by Toolmaker Quote
I didn't want the original Pentax adapter. That one was designed to stay with the camera so you could interchange screw mount lenses. I purposely wanted the flange type so I could leave it on the lens and still have it use the bayonet function.
I just remove the little spring (one screw) on the original style flush mounting adapters, and I have a dedicated adapter on most of my M42 lenses. I've never had a lens come off by mistake or issues with the lens rotating while focusing etc.
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