Fixing stuck aperture on Minolta 35-135mm Zoom w/ Macro mode
I recently acquired a 'new' (new to me) Minolta 35-135mm Zoom 3.5-4.5f with 1:4 Macro mode at 135mm. Unfortunately, I did not realize the aperture iris was not closing properly, in fact, for a bit I thought it was straight stuck open. With some help (read: more force than it should) I could get the iris to open and close by pushing on the aperture pin.
I did some research online regarding this lens, but found very little on it, and even less on repair guides. Getting it serviced was also a non-starter because the cost would be much higher than getting another lens. With some trepidation, I decided to do some exploratory surgery on the lens to see if the cause was something simple and fixable or complicated.
Starting from the back of the lens, I sketched a top down view of the back of the lens in case I would forget how some detail/alignment went back in. Another thing I do when reassembling older hardware is to put the same screws back whence they came from. This helps if there are minor differences that you might not realize. Documentation is key to success in this type of task. In this case, notes, scribbles and iPhone photographs work great to track progress.
I carefully unscrewed the larger 4 screws on the outer ring. This allowed the aperture selection ring to be removed from the body, including the aperture fork and its selector mechanism.
Once separated, I tested the internal aperture pin to see if the aperture itself is getting stuck. I was able to move it with a thin screw driver very easily, shutting open and close. Great news! This meant the problem was at the aperture selection ring.
In order to look deeper I removed 3 tinier screws that held a fuzzy coated dust shield in place. The dust shield was loose, but I also had to remove the locking catch by removing two additional screws on the side.
This part of the surgery involved understanding how the mechanism works. There is a shaped metal ring that selects the stop point for the aperture selector fork. It seemed like there was some sort of dried liquid in some parts, but not too sure if that was an accident or intentional - err on the side of caution and assume that 'its meant that way'.
I started to look into disassembling the aperture selector ring by looking for additional screws that were keeping it together. There were two screws holding a tab that seemed like a good place to start. As it turns out, with those removed, the aperture fork would freely move and snap back to place via the spring. Looking closer at the tab I just removed, it seems like the pin was rubbing the tab.
My guess? Sometime during the lens' ~20 year life, the pin had gotten whacked and bent enough to rub against this limiting tab, preventing the further intrusion of the pin into the lens mechanism but causing enough friction to prevent a snappy aperture return. A little gentle pressure to bend it back outwards, a few test fittings later and the tab was back in place with its screws. The aperture ring was much snappier now! I used some canned air to blow some of the dust of 20 years out of the mechanism, and reassembled the pieces of the aperture ring, and then replaced the ring back on the lens body, making sure the fork was lined up properly with the aperture pin.
Now the aperture works as intended!
Some test photos after the repair, both tele and macro modes:
