Minolta Lens Blades Opening Slowly After Being Stopped Down

[hanhasgotqi]

Hi All,

I just bought a Minolta MC Rokkor-PF 55mm f/1.7 lens (MC without stop down lever, 52mm filter thread) in very good cosmetic condition. The glasses are all clean. However, when I put this lens on my XD film body, I noticed that the aperture blades closing down instantaneously but taking 3-4 seconds to open up again. I do not see any oil on the blades.

I took the lens off the XD body, and manually opened and closed the aperture by rotating the aperture ring. The blades moved in and out instantaneously as well. Very snappy. Then, I closed down the aperture and manually moved the pin in the back to open up the blades, as what a Minolta film body would have done. The same behavior happened. I saw that a shorter pin in the lens mechanism in the back was slow to follow the longer pin that I nudged with my finger. So the blades opened up just as slowly.

Does anybody know if this is normal behavior with Minolta MC lenses? Or is there something wrong?

I tried this lens on a Minolta X-570 body, and the same behavior happened. Thank you in advance!

[Teemō]

It's not normal but I don't know the exact cause. I guess there will be old grease that has leaked onto the aperture movement pieces where it shouldn't. However, I cleaned and degreased these parts in a MC 35/1.8 and the aperture was sometimes very slow such that it would not be useable on a Minolta SLR but other times it worked fast enough. It's like the tolerance is bad and parts are rubbing against each other by a microscopic amount. It's an overcomplicated mechanism compared to MD lenses. I've taken my lens apart so many times looking for what should be a simple problem but can't identify the cause. I suspect it is friction because when the aperture would work quickly, it would only do so if I pointed the camera up, and sometimes flat, but facing down it would be too slow.
Mind you, my lens did have grease on the aperture blades when I bought it. I don't think any parts in the aperture assembly are supposed to be lubricated but I could be wrong.

[aidaho]

I have two 55/1.7. One in perfect condition, other one I bought for parts.
The mint one has instant aperture operation.

The one for parts opens up slowly.
I think the grease got to the base of the blades.

[hanhasgotqi]

[hanhasgotqi]

[Teemō]

[Lightshow]

Definitely not normal, any oil on the blades will slow them down to a crawl, I had to clean and relube my 58/1.2 and 85/1.7 a number of times because the path from helicoid to aperture is so short.

A little TLC and that lens will be as good as new.

[hanhasgotqi]

Thank you kindly for all your replies. I fitted this lens on a Fujifilm X-Pro1 and took some pictures at my local market. The image quality is superb, despite the rear elements in my sample having a significant amount of balsam separation or something resembling balsam separation. I'll have somebody try repairing the aperture mechanism to salvage this little gem.

[aidaho]

[Teemō]

The 55/1.7 is a good lens. I have the faster lenses but I've not been able to bring myself to sell the 1.7 yet. Which version do you have?

After many hours of calibration and fixing mistakes in the reassembly - which is what happens when you don't note down the way it was assembled in factory - I have restored my 35/1.8. Aperture is working quickly in every orientation now down to F16 which is nice because I've had it for years and every image I've taken has been stuck wide open, and usually out of focus lol! It's clear that any minor dry stains on and around the aperture blades will slow down the performance enough to prevent use on a Minolta SLR, and it probably benefited from rearrangement in case blades were distorted.

It's a pretty easy job with some careful patience. I recommend spending a bit on the few tools needed to do a whole CLA - they will quickly pay for themselves. The cheapest CLA I know is about 50 USD.

Screwdrivers: I highly recommend the drivers from Moody Tools, which are much harder and warp-resistant than Wera drivers. Their cross-point drivers are to JIS standard. They are all you'll need for working on Japanese cameras and lenses and can buy a 6-pack of slotted and 4-pack of JIS, I've never needed other sizes.

Oil: The oil I've used for the aperture mechanism is Moebius 8000 - pretty expensive but all I had. Probably something cheaper like sewing machine oil would do too - you only want it to 'wet' the surfaces, and not dry out. You'll need something else if you live around -15 Celsius temperatures. If you get the Moebius oil, don't screw the cap down too much or it will split and leak.

Grease: For helicoid grease I've used Helimax-XP Lithium & PTFE on a variety of thread sizes and found it to be very smooth. Some have found it to be too thick for anything less than telescopes but I think they applied too much. Others use 'Japan Hobby Tool' #30 grease for normal helicoids and #10 or a mix of both for finer threads.
Minolta lenses, like most, use a dense thread for the focus ring, and a loose thread for the helicoid. The dense thread is what allows you to turn the focus ring to 'push' the helicoid out, without the focus ring moving forward too much itself. It's also used for the fine-tuning and calibration of infinity focus. You clean out the old threads with detergent water and a toothbrush - you can also just use automotive degreaser and although a bit more effective, it's a lot more messy. I just apply the new grease with a lint-free cloth or paper tissue. Cycle the threads together, and wipe-off excess, repeat that 3-5 times or until it feels right.

1. Completely reassemble the rear first and mount it to a camera.
2. Insert the optical block and aperture unit ensuring that the aperture prong is held by the arm in the mount. Orient the whole unit so that at the minimum aperture setting, the aperture is actually closed down as far as it will go, and likewise for wide-open - then screw the unit down ensuring that it doesn't turn.
3. Find infinity focus on the camera using the split-prism and micro-prism on a object more than 500m away, put on the focus ring and screw it down at the infinity position - there's a screw stopper so you can't miss it!
4. Re-insert the filter thread/decoration collar and screw-in the nameplate.

For disassembly, you simply do the following in reverse, unless of course you're just tackling the aperture mechanism in the mount. There are videos for a few lenses on Youtube. Be careful about which screws you take out depending on the lens. On the 55/1.7, there is nothing securing the aperture ring down so if you take it off, you may lose the aperture click ball bearing and spring. I also just use a toothbrush and hot water to remove grime from the focus ring grip and you can do the same on the aperture ring. Don't soak them too long as the engraving paint can peel out. You can also use a wooden toothpick and go groove by groove.

[hanhasgotqi]

Yes, very good lens. I'll update this page once I've somebody open the lens up. Don't have the time to become a lens technician yet, but I can imagine how rewarding it is.

The images I took today with this Minolta MC 55mm/f1.7 looked a lot like another lens I have, the vintage Fujinon EBC 55mm/f1.8. An inexpensive standard lens for Fujica film cameras, but full of character too.

[hanhasgotqi]

[aidaho]

[hanhasgotqi]

Beautiful shots.

I think I have the MC-II version, with the knurled focusing ring.

[braz]

I have nearly a full set of MC lenses (missing 100mm f2), and have CLA'd most of them, including 5 or 6 copies of the 55mm f/1.7. The aperture mechanism should be completely dry, no oil or grease. Even though there is no oil on the blades, there's probably oil under the aperture arm where it lays flat against the barrel. This needs to be dry for the aperture to be snappy.

[hanhasgotqi]

[Mr.Bittacy]

I agree with you that the 1.7 is an amazing lens... I had a bunch of the Minolta 50mm ish lenses and ended up keeping the 1.7 and the 1.2, the 1.2 is amazing but for some reason I can’t get rid of the 1.7...

Whenever I get a Minolta lens with slow or oily blades now, I remove the whole aperture assembly and let it soak awhile In isopropyl and clean it that way, no lube afterwards. The lenses I have done this way have stayed clean and snappy where as if I tried to take a shortcut and just clean them with a q tip and alcohol in the body, the oil and slowness always came back quickly.

[hanhasgotqi]

[Mr.Bittacy]

I wonder if that is due to the fact that it was the kit lens so not many people took good care of them...There are some amazing Minolta disassembly videos on YouTube if you search for Matt beirner.

[aidaho]

[Lightshow]

[hanhasgotqi]

What do you mean? That you installed glasses from a Contax G 45/2 lens into the lens barrel of a Minolta MC 55mm 1.7? Or that what you are attaching to your camera body is a Contax G 45/2?