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lens mount on mdIII 28-85mm is loose
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PostPosted: Thu May 16, 2024 3:56 am    Post subject: lens mount on mdIII 28-85mm is loose Reply with quote
hello, i am a new member to this forum, but I was simply looking for some assistance in tightening down the lens mount on an MDIII 28-85mm lens that I recently bought off ebay. The glass is in very good condition, and the lens helicoids are fairly smooth still, but the lens came with its mount very loose. i have only very sparingly opened up some other film era prime lenses, so i thought this would be easy, but the lack of head screws (more unique rear assembly?) and the lack of service manuals online prevent me from figuring it out. can anyone give some advice/walkthrough on how to open it? or a link to any service manuals or pages covering the disassembly would be greatly appreciated Smile


PostPosted: Thu May 16, 2024 7:19 am    Post subject: Reply with quote
Welcome to the forum!

It has been a while since I last serviced one of these; the below is from memory and experience with Minolta lenses of the same era/construction:

There is a cover over the mount screws. Look carefully at the side of the edge of the mount (behind the aperture ring); you will notice three tiny slotted grub screws.

Unscrew those three grub screws (only a few turns each, no need to remove them completely).

Now the mount screw cover can be taken off, but in doing so take care to leave the aperture ring in place and don't lift the aperture ring away from the lens or you will be searching the floor for a 1mm diameter aperture click ball.

Carefully rotate the aperture ring a bit through its click-stops (again, do not lift away from the lens!) and four mount screws should become visible and accessible for tightening.


PostPosted: Thu May 16, 2024 8:18 am    Post subject: Reply with quote
Quote:
There is a cover over the mount screws. Look carefully at the side of the edge of the mount (behind the aperture ring); you will notice three tiny slotted grub screws.

Unscrew those three grub screws (only a few turns each, no need to remove them completely).

Now the mount screw cover can be taken off, but in doing so take care to leave the aperture ring in place and don't lift the aperture ring away from the lens or you will be searching the floor for a 1mm diameter aperture click ball.

Carefully rotate the aperture ring a bit through its click-stops (again, do not lift away from the lens!) and four mount screws should become visible and accessible for tightening.


Duly noted, I have experienced losing the ball bearing twice but have miraculously found them on my table not far away. I did manage to get that far in disassembly, removing the mount screw cover and rotating the aperture ring around to reveal the 4 screws underneath. The ball bearing did fall out, but I did catch it (I open the lens in a plastic bag because i do not trust myself with not accidentally lifting the aperture ring) and I did tighten the screws underneath; however, this did not seem to affect my lens mount that much Sad


PostPosted: Thu May 16, 2024 11:43 am    Post subject: Reply with quote
toostar wrote:
Quote:
There is a cover over the mount screws. Look carefully at the side of the edge of the mount (behind the aperture ring); you will notice three tiny slotted grub screws.

Unscrew those three grub screws (only a few turns each, no need to remove them completely).

Now the mount screw cover can be taken off, but in doing so take care to leave the aperture ring in place and don't lift the aperture ring away from the lens or you will be searching the floor for a 1mm diameter aperture click ball.

Carefully rotate the aperture ring a bit through its click-stops (again, do not lift away from the lens!) and four mount screws should become visible and accessible for tightening.


Duly noted, I have experienced losing the ball bearing twice but have miraculously found them on my table not far away. I did manage to get that far in disassembly, removing the mount screw cover and rotating the aperture ring around to reveal the 4 screws underneath. The ball bearing did fall out, but I did catch it (I open the lens in a plastic bag because i do not trust myself with not accidentally lifting the aperture ring) and I did tighten the screws underneath; however, this did not seem to affect my lens mount that much Sad


If the lens mount still feels loose, I can only think of two possibilities:

1) The mount isn't actually loose but the bayonet springs in the camera and/or adapter aren't tight enough.
2) The chrome part of the lens mount is loose relative to the black part of the mount. If that is the case this requires the whole lens mount to come off and be disassembled; the aperture actuator levers inside the mount need to be removed, and then the four internal screws that hold the chromed part of the mount onto the black part of the mount need to be tightened from the inside of the mount. It is very rare for those four screws to have come undone though, they are usually tightened very well in the factory.

Situation 2) is not exactly a recommended DIY beginner's task, or you will not only have a click-ball but also a couple of tiny springs flying around the place, and possibly a tiny C-clip also...


PostPosted: Thu May 16, 2024 2:44 pm    Post subject: Reply with quote
Quote:
If the lens mount still feels loose, I can only think of two possibilities:

1) The mount isn't actually loose but the bayonet springs in the camera and/or adapter aren't tight enough.
2) The chrome part of the lens mount is loose relative to the black part of the mount. If that is the case this requires the whole lens mount to come off and be disassembled; the aperture actuator levers inside the mount need to be removed, and then the four internal screws that hold the chromed part of the mount onto the black part of the mount need to be tightened from the inside of the mount. It is very rare for those four screws to have come undone though, they are usually tightened very well in the factory.

Situation 2) is not exactly a recommended DIY beginner's task, or you will not only have a click-ball but also a couple of tiny springs flying around the place, and possibly a tiny C-clip also...

Darn, sounds like I'll have to take this lens to get it repaired at a shop. The second situation where only the chrome part of the lens mount is loose sounds exactly like my situation, with it having some play relative to how the rest of the rear mount is rock solid. Thank you for the input nonetheless, it gave me some good insight into how lenses without visible rear head screws are assembled. Here's to hoping more of my Minolta gear doesn't stay in repair limbo...


PostPosted: Thu May 16, 2024 3:08 pm    Post subject: Reply with quote
On that note, could you give a hint as to where the ball bearing for the lens goes? I cant immediately find the recess that holds it, I'm thinking that it may be under the part of the aperture ring that I cannot fully lift up; there's a small two screws connecting the aperture ring on the inside to some metal piece?


PostPosted: Thu May 16, 2024 7:31 pm    Post subject: Reply with quote
toostar wrote:
On that note, could you give a hint as to where the ball bearing for the lens goes? I cant immediately find the recess that holds it, I'm thinking that it may be under the part of the aperture ring that I cannot fully lift up; there's a small two screws connecting the aperture ring on the inside to some metal piece?


The ball bearing goes between the aperture ring and the mount. Either the aperture ring or the mount has a small hole on the side with a spring in it (a tiny coiled spring, 1mm diameter, and only 2-3mm long). The ball needs to go on top of the spring, and then is depressed against the spring into the hole whilst the aperture ring slides over the top, trapping the ball against the spring tension. The ball will then click into a few detents resulting in the tactile click-stops for the aperture ring.

Some Minolta lenses have the hole (with spring & ball) in the aperture ring and the click-stop detents in the mount, other lenses have the hole (with spring & ball) in the mount and the click-stop detents in the aperture ring; I can't remember which way around it is for this particular lens.

EDIT: it can be difficult to spot the hole as the entrance of it is usually covered with grease.
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