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11-21-2012, 02:27 PM   #1
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Location: Houten
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Repair internal anti-reflexring SMC 500mm f4.5

Repair internal anti-reflexring SMC 500mm f4.5

Hello,

Since a week I am the proud owner of a legendary lens from the old days. It took quite some efforts to get ‘m here, and I must say, it is a beauty. Good preserved, all rings, focus as well as aperture, turning smooth, no eyecatching scratches but only caused by use, clean and untouched frontelement. It is ok. But,… there is a anti reflexring internal getting loose. The lens looks as if it is only used few times, but this ring rattles as you move the lens. The ring also nears the apertureblades, cautious for damage of them, and hits the inner surface of the last frontelement. You can wait for more damage.
I suppose that during shipping to my place, Holland, the lens got hit by strikes and bumps, allthough no damage according to this matter showed on the box. Still, these strikes could have happened when the box hits a hard surface in the full face and the lens was not packed, it is a heavy one, with bubblefoil all around. Or, the lens has been sold with the loose ring allready. I do intend to keep’m, so I am looking for a solution.

I suppose the frontpart of the lens with the sunhood, almost similar to the Takumar 500mm f4.5, can be removed, but I am anxious to do that. I don’t know exactly how the frontpart is assembled to the barrel. A ghosting from the Takumar shows me what the mounting is, thread(?) combined with some locksrews (?), but such a huge lens should have more than only a thread, considering the size and the weight. I suppose also that unthreading the frontpart takes quite some force, not to say a thing about how to hold this part, the barrel too, in your hands, cause it is too big! Such a force can easily destroy a fine construction.

Is there anybody whom has some experience with unmounting the frontpart of this lens ?

I really want to know what and how. Maybe there are some photo’s showing how to handle. The ring is glued, expected to be very lightweigthed, the glue did not hold.


pentaxior

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11-22-2012, 07:14 AM   #2
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Join Date: Sep 2006
Location: Mississippi, USA
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Posts: 558
I haven't been into this lens, but yes they can be held together with set screws and threads.The threads are extremely fine and from my experience, the threaded area is around an inch long. Makes for quite a good bond.
Mark your lens with some masking tape so you know where all the parts should end up upon reassembly.
Removal of the set screws requires a very good screw driver, a precision tool that fits the slot nearly perfect.
Once the screws are removed the barrel should unscrew without a lot of force. Rubber strap wrenches work if the bond isn't extremely tight.
Make your repair and reassemble. Be cautious with your lens barrel threads and don't cross thread them .

DISCLAIMER. If at any point a screw won't release....stop and find a lens repair person. A frozen screw requires you to drill it out and re-tap the hole.

All this being said, unless your mechanically inclined, send it to a lens repair shop. By education I'm a Mechanical Engineer and some times lens and small cameras are very tedious to work on.
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500mm, barrel, box, damage, f4.5, k-mount, lens, pentax lens, slr lens, takumar
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