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08-21-2019, 06:46 AM   #1
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Takumar 500mm F4.5 lens repair

Takumar 500mm F4.5 lens

I have acquired one of these beasts and am in the process of “restoring” it so-to-speak. This one has the “slight wobble” I have seen in the descriptions of ones for sale. I have it disassembled far enough to find the issue. There are three 2x5mm screws that hold the focusing assembly to the front part of the lens. In my case two were sheared off and the third had a damaged head. Being an old tool & die guy I have lots of experience with damaged and broken fasteners. I was able to remove the broken pieces so I am well on my way.

But I need some help.

The focusing mechanism is comprised of opposing right and left hand multi threaded helical splines that are keyed to each other so that when the cylinder housing them is rotated they move away or towards each other. I need to disassemble this mechanism for cleaning and re-lube. Taking it apart is easy. This is where I need help. What is the procedure for re-assembly ensuring I start the helical splines on the correct tooth and after that how do I make any fine adjustments? I am also in need of some screws. 2x5mm flat head screws. 2x6 will work also. I would also like to find a 1.7mm screw that's long enough to make a new pin. Probably 5mm long would work.

After all that I plan on making a drill jig to add 3 more screws to the helical assembly to help prevent this from happening again. If you were to hit the lens on it’s end about half the weight of this monster impacts the three 2mm screws. No wonder this is a common issue.

Thanks for taking the time to read this rather long note.

08-21-2019, 11:44 AM   #2
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You have to carefully scribe where they come apart. Scribe inside the groove on the inner helix and the edge of the outer helix. Pick any groove/edge. I am not familiar with how the lens is put together so I can't comment on how to adjust it.
08-21-2019, 02:37 PM   #3
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Just do a search on M2.0 x 5 screws and you should find a number of vendors online that will sell them by the piece.

For instance:
M2x5 Wafer Head Machine Screws

They also have M1.7 x 5 screws, your choice of head.

You can always cut/file down longer screws.

Last edited by Not a Number; 08-21-2019 at 02:43 PM.
08-21-2019, 05:59 PM   #4
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My Local Ace Hardware has a good selection.....No Kidding !

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