Lenses for Pentax

How to Dismantle and Clean a 50mm Lens

Posted by: Kit. on Tue Dec 13, 2011 16:49
Step by step instructions, with pictures, on how to dismantle and clean a 50mm lens....
Here is the Pentax 50mm F1.7 SMC-M, found by thoramay in a charity shop.

And here is the stuff we will use to clean it.

First job, is to remove the finishing ring, from the front of the lens.

This is done by cutting a double sided sticky pad into 4 pieces, and sticking them to the ring, as in the above picture.

We now place an M42 rear lens cap on the pads and press down firmly.

Unscrew the ring, in an anti-clockwise direction.

Now we can remove the filter threaded front tube. This is done by removing the three little screws, highlighted with white paint, in the picture above.

With the front tube removed, we have easy access to the front element retaining ring.

The element is held in place by the inner ring (marked white) in the picture, above.
The correct tool for removing these rings, is a lens spanner. I do not have one. Fortunately, they were not very tight, and I was able to undo them with my fingernails. The rings undo anti-clockwise.

With the ring removed, the front element will drop out.

We can now remove the second element assembly. If the retaining ring is tight and you do not have a lens spanner, a steel rule placed across the ring and located in the slots, can be used to loosen the ring. - But only if it does not foul the lens element!

The second and third element assembly also unscrews anti-clockwise.

Below, we see the second and third elements seperated

With the front group removed, we can turn our attention to the rear group.

Remove the five mount retaining screws.

DO NOT REMOVE THE APERTURE RING! - It is not necessary and doing so risks losing the tiny spring and ball baring within.

With the bayonet mount removed, we can now simply unscrew the rear group assembly by hand... Again, anti-clockwise.

Here are the two rear elements separated

Ideally, the rear element should be removed from it's housing, but the retaining ring was very tight and I could not undo it. Not really a problem, as we can clean it as it is.

Now that we have removed all of the glass from the barrel, We can set to cleaning.
Dip a cotton bud into the vinegar and swab each element gently. Leave the vinegar on the glass for a few minutes, to do it's work of killing the fungus.

After the vinegar treatment, wash the elements in soapy water. I used washing up liquid. Wash until 'squeaky' clean, then rinse well in clean running water to remove all traces of the detergent.
Dry immediately with a soft, lint free cloth.

Here we see the now cleaned elements laid out in order.

The lens is now cured of it's infection and can be reassembled.
Reassembly is of course, the reverse of the method we used for the strip down.

Here is our patient. - Reassembled this evening and fully restored to health.


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