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01-21-2012, 05:27 AM   #1
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How to fix a loose front lens?

I have bought a SMC M f 1,7 50 mm on Tradera (the Swedish brand of e-bay) which unfortunately came with itīs front (with the filter thread) loose . Atlhough it probably doesnīt affect the optical performances of the lens, it obviously completely ruins the quality feeling of older Pentaxī lenses, not the least with itīs rattling noise!
Before I go ahead with the hassle and demand the seller to take the lens back or make a reimbursement from the price (which btw was 75$, not very chep either), I would like to know if it is possible to fasten it and how difficult it is to disassemble the lens to do it. I have heard of people who have done that, and although I am hesitant to try it myself, I would like to know how to do it. The alternative is to send it to a workshop to get it fixed, but Iīm afraid that would be unproportionately expensive. Besides I have a Takumar M42 f 2,0 55 mm with the same issue, although not as servere, so it would be nice to know how to do the operation and fix both!

01-21-2012, 06:52 AM   #2
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The front trim ring (usually with the lens details printed on) - threaded area where filters mount - unscrews, once removed you can access the screws beneath which hold the front lens assembly - this is probably only loose, tighten with small jewellers style PK screw driver. The trim ring is a bugger to get off but if you search this site you will find the methods used by others to get it off.
01-21-2012, 07:22 AM - 2 Likes   #3
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First you need to determine if it is indeed just the filter ring that is loose, or if it is the entire front section, including the lenses. If the filter ring moves but not the front lens element (glass), then it should be easy to tighten. If the entire front feels loose (including the glass elements) it is still likely easy to fix, but more involved.
The first step is to unscrew the "name ring" from the front of the lens. It is just threaded into the filter ring. Before starting on it, use something like an old toothbrush to clean any accumulated grit out of the filter ring threads. (It's a pain to have the name ring jam tight as you try to remove it!) You unscrew the name ring by finding a rubber stopper or tube of the right diameter to fit against the name ring inside the filter ring, but not touch the glass. The friction between the rubber stopper and name ring is enough to unscrew it. If you can find any kind of tube the right size (I've used a piece of plastic pipe on large lenses), you can stick strips of double-sided foam tape (like used to mount pictures on walls) to get a grip between the tube and name ring.
Once the name ring is removed, on the SMC-M you will see that the filter ring is just mounted with three small screws that can be tightened with a jeweler's phillips driver. (Some lenses use slotted, some phillips.) There are three other screws about the same size that go through cutouts in the filter ring - don't mess with these. Then just screw the name ring back in.
If this isn't the problem with the SMC-M I'd return it.
The super Takumar may have the same three screws, or more likely the filter ring is just a threaded tube that unscrews from the main body. It was originally fastened with glue for a thread-lock, but I have found them loose. However, I bet you will find the entire front of the Takumar is loose to move around a bit. On the Takumar this can have a couple of causes. Most common is that the grease that fills the helical focusing threads has oozed out leaving the threads a sloppy fit. The threads aren't worn out - just dry. I've found Takumar, Minolta, Exakta, and other well-used lenses so loose and rattle prone that I was sure something had come loose, only to find cleaning and re-greasing the helical made them feel like new. If it's the helical threads the front section will move a bit back and forth, in and out, rocking, etc. This is a bit involved, but the Takumar lenses are easy to understand. If you have interest, you can find the old service manual with parts assembly diagrams and basic instructions available on the Web.
The other common issue with screw-mount Takumar is the helical guides that keep the inner lens parts from turning when you focus. These ride in slots, and need to fit tight or there is some play back-and forth (turning). To make it fit with no play, one of the guides is split like a fork, with the ends spread apart so they fit tightly in the slot. The problem with screw-mount lenses is that the guide only contacts on the far end (from its mounting point) when the lens is at near-focus. When people remove the lenses from the body they often turn it by the front in this position, so it tends to bend the forked guide and loosen it up. It can also bend both guides enough to cause other problems. So always mount and remove a thread-mount lens when it is focused at infinity, using the entire body, not the focus grip or front section. These bent guides are also easy to fix - but it requires a full disassembly of the lens body.
01-21-2012, 08:27 AM   #4
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Wow! You certainly have a wealth of knowledge! Thanks to your advice the front filter ring of the SMC-M lens is already fixed! The ring with the name and numbers on was a bit loose, so I could unscrew it from the filter thread with my nails! Underneath it are the screws you mentioned. Mine were Phillips, and with my smallest slotted screwdriver (my smallest Phillips was a size too big, I think) it was easy to fasten them. I will have a look at the Takumar 55 mm with the same problem when time comes (Iīm more into K-mount lenses, since I donīt like the stopping down aperture procedure).
This site is awsome! I hade figured to get an answer maybe in a few days at best, not being sure I could use the advices I hopefully got, and now the lens is already fixed! My support has already paid itself back many times.

01-21-2012, 11:52 AM   #5
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Glad it was easy! These screws are normally sealed with a small dab of paint to keep them from loosening, so next time you have the name ring off...
01-22-2012, 10:10 AM   #6
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Tom, thanks for your advice!
I have had the same issue as the OP (actually also with the smc M 1.7/50). As you have described, it was an easy fix.
10-08-2013, 12:25 PM   #7
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TomB and others... your directions on how to do this simple fix saved the day for me today, after acquiring an SMC-M 1.7.... I used a plastic Pentax body cap and rubber band to press & gain traction to spin off the name ring, and access the loose screws... I'll have to remembe r the paint trick next time! THANKS FOR YOUR HELP!!
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