Mamiya Sekor C 45mm 2.8 Loose Focus Ring

I recently disassembled my 45mm to fully clean the aperture blades as they had oil on them and wouldn't consistently open or close. I couldn't find any definitive guides to do this so I just had to figure it out along the way. After getting it clean and put back together the focus ring is no longer locked with the outer element so it just spins freely. It still stops at the designated ranges but only adjust focus if you squeeze it with a lot of pressure. As far as I can tell there are no screws that hold it into place so I'm wondering if it was attached with glue or some other method. I'd love to use it again now that the blades are finally clean so I'm hoping I haven't done any irreversible damage. Any help getting the focus ring locked again would be greatly appreciated.

Was there any evidence of glue when you disassembled the lens ? Is there a hole for a screw, even just one hole ?

 

If you post the brand of the lens, other members may be familiar with how it goes back together

No holes or screws on the focus ring. The only evidence of glue is on the outer element and it seemed to be a small dab to hold it in place. I had to break it to unscrew the element.

Is this the lens ?

 

 

 

This Pentax f1.4 lens has three screws. It's a very similar looking lens and I just removed the front barrel part to see how the focus ring is attached

 

That's pretty close but I think I've got an older version. Here's the lens I'm working on. With the front element removed there are 6 screws visible. 3 of which attach the flared out metal housing for the element, the other 3 hold the aperture assembly into the barrel.

 

 

 

I've got it broken all the way down to just the outer barrel and the outside black ring spins freely on the inner silver ring but isn't threaded and won't detach. I'm assuming that these should not move separately and maybe the outer ring was glued to the inner and I broke that seal in my taking the lens apart. Hopefully not the case but I can't see any other way to fix the focus ring to that inner ring.

Any fixing screws are generally hidden under the rubber grip. Have you lifted the rubber sleeve to see?

 

A glued focus ring would be very unusual in a lens of this vintage. I haven't taken my 45mm lens apart - no need, but I've dismantled a Mamiya Sekor 70mm leaf lens. No glue holding anything in place, only screws.

 

BTW, I hope you marked the point at which the helicoid inner and outer parted company. Otherwise you'll have a frustrating time trying all the different combinations of thread 'start' before finding the proper infinity focus point.

 

Incidentally, the 77mm front ring 45mm lens was re-computed and replaced with an 'S' (presumably for small) version. This was a much-needed upgrade, since the old lens was very soft at the edges and corners. The 'N' version retained the optical formula of the S version, and only the cosmetic design was changed.

Edited July 15, 2018 by rodeo_joe|1

Thanks for the info. There was one small screw under the grip but it's the one that stops it from rotating past the end points.

 

Unfortunately I didn't read about marking the helicoid so I've been dreading that aspect of the reassembly as well.

There was one small screw under the grip but it's the one that stops it from rotating past the end points.

 

So you removed the rubber hand grip and saw a small screw underneath ?

First of all, be certain it's not a locking screw. Try screwing it down and see if it locks the focus ring to the helicoil

 

Another question though - does the ring with the rubber on it turn separately to the focus distance numbers ? In other words, is there two rings, one with the distance numbers, and one with the rubber grip ?

 

The helicoil looks like an eight or ten start thread, no need to panic, you only have to number each "start" (each thread) and try each one until infinity comes up against it's respective stop, when you're reassembling it

The numbers are printed on the same ring as the rubber grip and it spins freely on the silver barrel. There is a very small amount of play between the two pieces if you push them front or back.

 

Here's a picture of the back side. You can actually see the screw under the grip to the bottom right. The piece that threads onto the back of this has a lip that catches that screw and stops the gauge at the near/far markings.

 

Also, thanks for taking the time to reply, I appreciate it.

 

Yes we're back to square one but things are a bit clearer since you've posted those photos

 

It's obvious the the focus ring has come adrift from the helicoil but if there's no other screws under the rubber grip then it's difficult to imagine how the two parts held tightly together and still be a permanent good quality fixture. I wouldn't put it past Mamiya to use glue, I've seen some shoddy production and design work in some of their lenses and bodies

 

If it was glue that they used, probably not enough was applied around the ring. If they didn't use glue , there is really only two other ways that could be used: by using locking screws, or somehow clamping the two parts together. Both of these don't seem to be the case from what you've explained about the problem

 

Whatever you do to lock the two parts together, you must make sure the distance numbers correspond with the position of the helicoil at "Infinity". You have a big job ahead of you. You need to do an Infinity Focus Test by using a frosted screen taped to the film plane in the back of the camera and with the lens reassembled turn the helicoil till you get sharp focus of an object no less than a quarter of a mile away. You may have to use that method of "squeezing" the focus ring to turn the helicoil to arrive at the sharp focus

 

Then you need to turn the focus ring till "Infinity" is opposite the arrow, then using a "G" clamp, lock the ring to the helicoil and remove the lens from the camera, after which, mix some slow setting Araldite, heat it slightly till it runs easier and pour it in place/s around the inside of the ring keeping it away from the "Stop" screw

If the outer grip ring was only glued to the helicoid, then it should now be free to lift away from the helicoid. You say it isn't and that something is holding it in place. That sounds like a screw in a groove to me.

 

If the ring was glued in place, then it'll have to be completely freed from the helicoid to re-apply glue to it.

 

"I wouldn't put it past Mamiya to use glue, I've seen some shoddy production and design work in some of their lenses and bodies"

 

- Really? All the M645 gear from that era I've had has been really well built. It was only with the terrible plastic Super, E and Pro/ProTL bodies that Mamiya build quality took a nose dive. Even then, the N series lenses were well made. Shame that the placky camera bodies and magazines fell apart!

 

Anyway, given the tendency for oily aperture leaves to re-oil themselves quite quickly, my advice would be to sell the lens if you ever get it back together in a presentable state. As previously mentioned, that big ole 45 is pretty awful optically. Replacing it with an S or N version wouldn't be a bad idea at all.

At this point I may have to take your advice rodeo joe. I've got more time sunk into this than I care to admit so it may serve someone else better as a parts lens. I appreciate the help from you both.