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Minolta 50/1.4 AF spring mechanism repair

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DrDave View Drop Down
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Post Options Post Options   Quote DrDave Quote  Post ReplyReply Direct Link To This Post Topic: Minolta 50/1.4 AF spring mechanism repair
    Posted: 26 January 2022 at 06:13
Hi--I'm trying to repair my trusty 50/1.4 Minolta AF 50/1.4.
The iris was sluggish, so I took it apart and cleaned the blades, something I have done a few times, but they were clean.
I then noticed when I pulled off the back mount that it is the lever and spring that are slow. The spring looks OK. I don't see anything bent. I'm guessing the oil inside the ring has clogged.
Anyone know how to fix this? I don't want to add more oil and have it drip onto the aperture blades.
All my other Maxxum/Rokkor snap back with a click, this one is molasses, even when removed from the camera, so it isn't the iris.
Thanks.
 



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addy landzaat View Drop Down
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Post Options Post Options   Quote addy landzaat Quote  Post ReplyReply Direct Link To This Post Posted: 26 January 2022 at 07:53
Maybe these pictures of disassembly and Repair of Minolta AF 50mm f/1.7 and f/1.4 Lenses by Pete Ganzel helps: https://pbase.com/pganzel/disassembly_repair_of_maxxum_50mm_lens
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Post Options Post Options   Quote Phil Wood Quote  Post ReplyReply Direct Link To This Post Posted: 26 January 2022 at 15:58
Sounds like you need to clean out the old gung before adding any new. Remove all glass and use acetone (sparingly).
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DrDave View Drop Down
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Post Options Post Options   Quote DrDave Quote  Post ReplyReply Direct Link To This Post Posted: 27 January 2022 at 01:40
Originally posted by addy landzaat addy landzaat wrote:

Maybe these pictures of disassembly and Repair of Minolta AF 50mm f/1.7 and f/1.4 Lenses by Pete Ganzel helps: https://pbase.com/pganzel/disassembly_repair_of_maxxum_50mm_lens

Thank you, I did look there first and it looks doable, but but with these drawings I never know how much to remove or the pitfalls in reassembly. I suppose I could buy one for parts and just swap out the mount.
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Post Options Post Options   Quote japp Quote  Post ReplyReply Direct Link To This Post Posted: 14 March 2022 at 09:13
well, have you taken off the mountring and with that tried to let the spring do its work? i have hade this before and it looked like i turned the screws of the mount a bit to strong wich let to the spring not doing its work any more. so first look at that and if the spring works out of the lens than look if somthing is blocking the way for the spring
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Post Options Post Options   Quote DrDave Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2022 at 01:10
Yes, I've tried that, thank you. I think I will have to take it apart somehow or risk spraying some dry silicone.
 



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Post Options Post Options   Quote dxqcanada Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2022 at 22:33
I assume you did not take it apart to be able to remove the individual blades for cleaning ... sounds like you will have to do so.
Do NOT spray stuff in there it will just make it worse.
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Post Options Post Options   Quote ffrolvaag Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2022 at 15:06
I know, late to the party. Hopefully you were able to resolve the issue. However, in case you didn't, here is my experience with this (50mm F1.4) and other Minolta lenses that have a sluggish aperture.

Assuming you didn't do so, I would recommend that if the aperture is still sluggish the best thing to do is disassemble and clean the individual blades in the iris assembly as well as the two plates of the assembly. This means to take the plates apart, remove all the individual blades, and clean each piece individually. I typically use a solvent like Isopropyl alcohol, methanol, acetone or hexanes (hexanes if the lubricant is silicone based) that will dissolve the lubricant. Depending on the oil, something like a dish detergent may be gentle enough to remove the oil. The advantage of solvents is that they will evaporate quickly, but if too aggressive may remove paint from the blades. Depending on the lubricant and solvent used it may take a couple of times to remove any residue. Make sure all parts are dry and debris free before reassembly. Any lubricant or debris in the blades are enough to cause a sluggish aperture, as it is designed to be clean and dry. Also inspect the blades for bends or damage, as that could be the culprit too.

I would make sure to take some good pictures of how the blades are lined up (although Pete does have some good one). The 50mm 1.4 is a fairly easy lens to repair. The most difficult part of the process is the reassembly of the iris. It is difficult to get the to overlap of the blades correct so you can fit the moving plate back on. However, once you have done it once, it does get easier once you figure out the little tricks in how to move the blades to align them.

I would also recommend that you use the lever on the moving plate to get a feel for if the assembly glides easily, binds, or if any residual oil is in the assembly as you actuate it several times both before and after assembly.
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Post Options Post Options   Quote RonnieJ. Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2022 at 17:30
I just went through mine (oily blades). This video helped which I found much better than stills. Good luck with getting your lens working.https://www.youtube.com/watch?v=5QZErRdA84I
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DrDave View Drop Down
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Post Options Post Options   Quote DrDave Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2022 at 19:43
Thank you, I also thought that was a good video. My lens is not sticking in the blades, it is in the ring with the spring. If you pull the mount off, it sticks even when not attached to the lens.
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Bob J View Drop Down
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Post Options Post Options   Quote Bob J Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2022 at 20:31
I had similar on a beer can many years ago.
There is a certain amount of interchangeability between some of the old Minolta lenses. I got the beer can going by using the rear bayonet and rings from a 35-70...
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DrDave View Drop Down
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Post Options Post Options   Quote DrDave Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2022 at 00:45
Originally posted by Bob J Bob J wrote:

I had similar on a beer can many years ago.
There is a certain amount of interchangeability between some of the old Minolta lenses. I got the beer can going by using the rear bayonet and rings from a 35-70...

Good idea! Thanks.
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DrDave View Drop Down
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Post Options Post Options   Quote DrDave Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2022 at 00:51
Originally posted by ffrolvaag ffrolvaag wrote:

I know, late to the party. Hopefully you were able to resolve the issue. However, in case you didn't, here is my experience with this (50mm F1.4) and other Minolta lenses that have a sluggish aperture.

Assuming you didn't do so, I would recommend that if the aperture is still sluggish the best thing to do is disassemble and clean the individual blades in the iris assembly as well as the two plates of the assembly. This means to take the plates apart, remove all the individual blades, and clean each piece individually. I typically use a solvent like Isopropyl alcohol, methanol, acetone or hexanes (hexanes if the lubricant is silicone based) that will dissolve the lubricant. Depending on the oil, something like a dish detergent may be gentle enough to remove the oil. The advantage of solvents is that they will evaporate quickly, but if too aggressive may remove paint from the blades. Depending on the lubricant and solvent used it may take a couple of times to remove any residue. Make sure all parts are dry and debris free before reassembly. Any lubricant or debris in the blades are enough to cause a sluggish aperture, as it is designed to be clean and dry. Also inspect the blades for bends or damage, as that could be the culprit too.

I would make sure to take some good pictures of how the blades are lined up (although Pete does have some good one). The 50mm 1.4 is a fairly easy lens to repair. The most difficult part of the process is the reassembly of the iris. It is difficult to get the to overlap of the blades correct so you can fit the moving plate back on. However, once you have done it once, it does get easier once you figure out the little tricks in how to move the blades to align them.

I would also recommend that you use the lever on the moving plate to get a feel for if the assembly glides easily, binds, or if any residual oil is in the assembly as you actuate it several times both before and after assembly.

Thanks so much--the problem is not in the blades because when I remove the ring, the ring all by itself is sluggish. I did however clean the blades as I have for the last twenty years or so.
It's actually fine for video, it just won't get out of the way for photos.
I rented the new 50mm 2.5 since I had to rent a camera anyway and I was surprised at how much better my ancient 50 1.4 is in the corners at F4. Still a great lens.
Oh and I mess up the iris every time I clean it. Whatever I learn gets forgotten a year later.
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