Unsuccessful Repair of a Takumar 135mm f/3.5 Telephoto Lens
This 135mm Takumar prime lens unit provides a modest telephoto view and was quite popular with Pentax single lens reflex cameras. It was made by Asahi Optical. It has a screw in camera mount. While it could be adapted to some digital SLR cameras, it has no coordination with automatic cameras.
While opening and closing the aperture the aperture ring suddenly tightened up and then froze between the f/4 and f/5.6 positions. The ring would wiggle freely back and forth about half a degree of rotation but was otherwise stuck.
We researched various web pages regarding repair of stuck aperture rings and diaphragms but did not find any articles for this lens.
We were able to unscrew the front group of lens elements which was a single module. When we looked inside the barrel, there were no screws we could undo except for three little spring tabs that gave the aperture ring its click stops at the marked f-stop positions. We found that the 2 or so inch diameter thin silver ring in front of the aperture ring snapped out from the front leaving three 1/16'th inch ball bearings in a groove and spaced evenly around the lens barrel where one of the ball bearings engaged the aperture click stops. The screws holding the spring tabs appeared to do nothing more than hold the spring tabs and ball bearings in place.
There was a 1-1/2 inch or so C shaped brass retaining ring visible inside the barrel from the front that we were able to remove easily. A 1-1/2 inch black washer defining the maximum aperture and also all of the diaphragm leaves fell out. But the aperture ring around the outside was still frozen.
The front of the lens barrel was wider so there was no way to slip the aperture ring off the front. So we had to dismantle it from the rear.
We undid some screws to take the silver rear shell with the depth of field markings off and also remove the stop that limits the rotation of the black focusing ring (shell) and also a few other screws. Now we could keep turning the focusing ring so the front section of the lens barrel unscrewed completely out of the rear section with the focusing ring itself.
We unscrewed the one inch or so diameter rear lens element module and looked inside where the diaphragm leaves used to be. No screws we could undo.
We then undid three small screws around the outside holding the black aperture ring on. This ring was now loose but would not fit over the threaded section of the barrel that engaged the focusing ring. So we removed a tiny screw that locked the various parts of the lens barrel in place rotation wise and, with a little effort we unscrewed the rear half of this front section of the lens barrel. In our case we were unable to unscrew the 1-1/2 inch or so diameter black retaining ring reachable through the rear of the barrel but were able to unscrew the barrel section a fraction of a turn using miniature wrenches similar to engine oil filter removal wrenches and then unscrew the retaining ring..
After the black aperture ring was removed we found that there was a second rotating ring inside to which the former was attached and which was frozen to the barrel itself.
We were now down to two pieces, the black front half of the front lens barrel assembly and the black inner aperture adjusting ring. The problem was between the two. And there were no screws to undo that would separate these two pieces.
A little tapping failed to make the inner aperture ring slide backwards off of the barrel.
Perhaps the inner aperture ring would slide off if it were rotated to a particular position and then pins engaging a circumferential slot would line up with and slide through front to back slots. Except we could not rotate the ring.
At this point we decided to do something destructive. Cut a slot across the inner aperture ring (turning it into a C shape) and then pry the slot wider and the ring would finally slip off.
After doing this we discovered that the inner aperture ring screwed onto the lens barrel in a manner similar to the lens elements' screwing into the barrel or the entire lens unit screwing into the camera. Apparently dust or a frament of worn off aluminum jammed the threads. It would have required several revolutions to get the ring off whereas it would move only one half of one degree.
We found some deformation of the threads suggestive of a scratched LP or 78 RPM or Edison cylinder record. Although the aperture ring was still tight enough to screw back on, we could not get it to work smoothly. Actually it was useless as it stood. Depending on where we held it, with its C shape it would either compress, preventing turning, or it would expand and slip off the threads.
Our final conclusion was that this aperture ring jamming problem was truly irreparable (other than by replacing the barrel section we mutilated) and therefore there was nothing to lose with with our destructive act of cutting the inner aperture ring.
Last updated April 28, 2011
Go to other, unrelated, topics
All parts (c) copyright 2011, Allan W. Jayne, Jr. unless otherwise noted or other origin stated.
If you would like to contribute an idea for our web pages, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.