I think we’ve all been here, buying a camera and lens rated by a seller as “very good” and not realizing all the photos had the lens caps on. When the Minolta X-370 with this lens arrived, opening the box filled my living room with a smell like broccoli and fish had been dumped in a bucket of milk and left in a car’s trunk in the summer. The camera was completely unrecoverable and the lens was filled with fungus and rust.

Most people would, rightly, have sent the thing back or dropped it in the recycle bin. I thought it might be fun to see how it worked and if I could repair it enough to take serviceable images. The end of this article contains a video detailing the process and providing more results.

To start, I put the lens on my Sony A7S II and took it around a local park for some sample photos. The rust on the lens’ elements tinted all the images brown. The mold, dirt, and rust gave the images a pictorialist quality. Some work in Photoshop CS6 Extended, primarily having to do with duplicating layers, correcting curves, and changing layer blending modes, pulled about as much out of the images as possible. I could restore the colors very well and through the blurriness could see hints of sharpness.

I tried both film and digital images and found the film images unusable and uneditable. This surprised me a bit as I’d expected they would be more so. More surprising, the black and white roll that I shot returned nothing that approached usable. Again, I had expected black and white film to perform better than color film.

Disassembling the lens revealed that the rear lens cell had significant rust damage. To repair the lens, I disassembled the cells with a spanner wrench and removed them. I cleaned them with rubbing alcohol (91%) and gentle application with cotton swabs to remove the mold and rust from the lens. This also removed the black edging on the lens elements.

Moldy and Rusty Minolta 50mm f/1.7 Rear Cell

Lens elements’ edges are ground and, in quality optics, also painted black. This absorbs stray light reflections that occur within and between lens elements and helps eliminate flaring, ghosting, and contrast loss when the lens has bright light either in the field of view or immediately outside of it.

Applying Culture Hustle Black 2.0 to the ground edges of the lens cells

Replacing the black coating was simple. I used Culture Hustle Black 2.0 to re-paint the edging. This had the advantage of being a better material than the original for this task and, though I can’t directly prove this because of the multiple repairs on this lens, I suspect this had a lot to do with improving contrast in the repaired lens’ images. I used a cotton swab to apply the paint and then a clean swab to remove bits of over-paint from the elements polished surfaces.

This is what the lens cells looked like after cleaning and edge repainting. The cell disassembly was simple and the cleaning, though time consuming, was not particularly challening.

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Cleaned lens cell

I also tried to repair the aperture, but the leaves had rusted and a number had broken beyond repair. Aperture leaves close because of simple mechanical action. In their basic design, aperture leaves have a fixed rotational axis with movement controlled by rotating pin that moves through a sliding pin track. The rotational axis causes the leaves to move around that pivot point, which directs them to close inward. In the leaves in the image below, that axis is the small circle.

Aperture Leaves exhibiting significant corrosion

Apertures convert the rotational energy of the aperture ring to inward motion by using a pin in the leaves’ longer slot. That pin slides with the aperture ring’s rotation and that rotation causes the leaves to close and move at the axis. In the leaves below you can see rust at the small holes. This caused the axis pins to fall out. In this lens, the axis pins are simply pressed and mushroomed into the leaves and the water in the lens caused a differential-metal reaction which accelerated rust at the pin location. This rendered the leaves unusable because they could no longer rotate at the axis point.

All this to say the repaired lens can only shoot wide open as I had to remove the entire aperture assembly.

So how does the repaired lens perform? Well, here are some sample images.

Overall, this lens performed far better than expected both before and after the repair. There is some softness and a pleasing glow in the post-repair images, and I don’t think I know of a lens that can truly replicate that. Surprisingly to me, the lens retained significant sharpness and, given that all the photos following the repair are shot wide open, it looks pretty darn good.

For more information on this project and a more detailed description of the repair, check out my video on this moldy lens repair at the video above!

~ David

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About the author

David Hancock

David Hancock is a professional writer and photographer in the Denver metro area. He specializes in dog, portrait, and event photography. David is most well known online for his film and technique-oriented...

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