Most Minolta lenses with SR mount are out of production since the late 80’s, with the oldest lenses being produced in 1958. Buying them today therefore means buying more than 30 year old equipment. The lenses have seen the world in decades of use or have been in storage for equally long periods. And like all mechanical parts, they need a little maintenance from time to time.
The most common defects seen in old lenses are dust inside the optical system, scratches to the glass and paintjob, bend body parts from being dropped or hit, oily aperture blades and mold or fungus infections. Dust and dirt inside the focusing helicoid are also more likely than in modern lenses, mostly because the vintage ones had more time to ‘collect’ it.
Mechanical damage and signs of wear on the outside
Some defects are easy to repair, some are better left untouched. Scratches in lens elements should be considered permanent, as it would require you to precisely ground, polish and re-coat the lens to achieve the same optical properties as before. This can’t be achieved without purpose-built high precision tooling and measuring equipment. Therefore, repair attempts on the glass usually do more harm than they do good.
Lens bodies where exclusively made from aluminum and brass before plastics became popular in the 90s. That made vintage lenses mostly heavy but very durable. Brass and aluminum where used for the mechanics inside the lens and aluminum for the body. However, aluminum is a rather soft metal and will easily deform when stressed mechanically. It is noteworthy that once bend, aluminum becomes very brittle, too. When you try to bring a deformed part back into it’s original shape, you should therefore look out for conglomerates of very fine crack-lines appearing on the metal surface. If you can spot those, the metal may break abruptly when stressed further and it’s probably time to stop.
After all, repairs might leave visible marks themselves or – in case of a fresh paint job – remove the patina and kill the vintage feel of the lens. This should always be considered before attempting to fix purely cosmetical flaws.
Disassembling the lens
When it comes to internal damage, most vintage Minolta lenses are surprisingly good to service. As long as you know how to dis- and reassemble the lens, cleaning most parts requires only a little patience and no special tools. Some valuable sources on how to disassemble Minolta lenses are listed in the links section. My recommendation would be to start with Matt Bierner’s Youtube channel, as he offers easy to follow step-by-step guides. Also, in my opinion, actually seeing somebody do the work is very helpful.
Cleaning the mechanics
Over the years, dust, sand and other particles may settle in the lens and creep into the mechanics. Often, particles get into the focusing helicoid and cause that typical grinding feel and sound when focusing the lens. On some occasions, the lubricants may also have decomposed over the years, leading to parts being either too hard or too easy to move. In any of those cases, the mechanics should be thoroughly cleaned and re-lubricated, to prevent further damage. Keep in mind that taking apart the focusing helicoid usually means you have to re-adjust the infinity focus of the lens afterward. Taking photos after each step of the disassembly process can be very helpful.
For lubrication, small amounts of acid- and resin-free grease will do. You don’t need any exotic stuff. The viscosity should be high enough so the grease does not flow or creep away from his designated point of use, even if the lens is left sitting in direct sunlight. This should be tested before applying it to the lens. Teflon-based lubricant is a good and modern alternative to regular grease. It is suitable for a wide range of temperatures and does not decompose. A first test with an MC Rokkor-PF 58 mm f/1.4 in which the lubricant had aged and got much too viscous showed good results. In this case I tried Robbe 5532 universal lubricant, which is originally intended for RC models. The resistance is a little higher than in the best Minolta MC lenses, but focus is extremely smooth and uniform again.
When there’s one place in a lens where grease is not good, it’s the aperture. The aperture in classic Minolta lenses works with a spring-loaded mechanic, in which the spring keeps the aperture closed at the value you preset. The aperture lever of a classic SLR counteracts the spring, keeping the aperture open for focusing and metering. Only for the shutter release, the lever is set free so the aperture can be closed with help of the springs tension. As the tiny spring is not very strong and the aperture blades offer a large contact area when opened, the mechanics have to work very smoothly. Oil on the blades increases the contact forces between them and counter-intuitively reduces the mechanics smoothness which is why it has to be removed.
Cleaning the aperture requires a little more sensitivity then the rest of the lens. As the aperture blades themselves are only 1 or 2/10th of a millimeter in thickness and the aperture mechanics are equally fragile, you have to be careful when working with them. Oily blades are the easiest to clean when you completely remove the aperture assembly from the lens body, disassemble it and wash everything with isopropanol (isopropyl alcohol). This method, however, requires a lot of time and it’s usually a pain in the a** to put the mechanics back together. As a starting point, I therefore recommend to grab some cotton swabs, some isopropanol and a little bit of patience. Wipe the still assembled aperture from both sides with the alcohol-infused swabs, wait a second for it to evaporate, open / close the aperture two or three times and repeat. After 15 to 20 turns, the aperture should be clean and can be dried carefully with an air blower (see tools section). This method also prevents the risk of damaging the blades during dis-/reassembly of the aperture.
A common problem with lenses stored in dark and humid basements or attics is fungus. Fungus presents as very fine, mostly white web-like structure on glass surfaces that can sometimes only be visible with the help of a flashlight. It might seem irrelevant, as you can hardly see it in the beginning. But the metabolism products of the fungus can actually dissolve the coatings and the glass (!), resulting in permanent and irreversible damage. Therefore, fungus should be removed from a lens or deactivated as soon as it is detected.
Killing fungus in lightly infected lenses is best done by exposing the lens to intense UV light. Sunlight for a day will do the trick, but also heat up the lens quickly and therefore is not the best solution. Sunlight is also useless indoors, because regular windows absorb most of the UV light coming in. A UV flashlight or lamp is the better way. As the UV will kill the fungus, but not the fungal spores, you need to impede further growth. To achieve this, infected lenses – like all lenses – should be stored in an absolutely dry and preferably well lit environment. Exposing the infected lenses to UV again from time to time won’t hurt, either.
An additional treatment possibility to not only disable the mycelium but also kill the invisible fungal spores can be ozone. Since ozone is nothing more than a highly reactive oxygen molecule (O3), the gas oxidizes many organic compounds on contact and should kill the spores. As a bonus, it also kills off most odors – great for lenses which have that particular “basement smell”. Because it is so aggressive towards organic components, ozone should only be used outdoors or in very well ventilated rooms where no humans are around. And there are some problems with the gas, too: First off, ozone tends to attack rubber parts after prolonged exposure. In my experiments, four to six hours were okay. After eight hours, the rubber smelled freshly vulcanized. Anything more than that would probably not have ended well for the material. The second problem is, that ozone of course cannot reach sealed compartments in-between lens elements. This is, where UV comes into play again. So in the end, a combination of UV and ozone treatment is my preferred solution to deactivate/kill as many of the fungus as possible.
For heavily infected lenses, killing the fungus isn’t enough. If the growth starts to impede image quality, there are three options: Live with it, dispose of the lens or clean it. A word of caution if you decide to attempt to clean yours: As fungus is the same as mold, it should be considered a health hazard. I recommend wearing gloves, protective glasses and breathing protection when cleaning it. This also indicates that your living room or kitchen might not be the perfect place to do this. As with all potentially toxic substances, concentration and exposure time are key. Therefore, carefully cleaning your workplace with disinfectant and venting the room after working on fungus-infected equipment reduces the health hazard. As does spending as little time working on the infected lens as possible.
Cleaning lens elements
As soon as the mechanics are fine, the next step is cleaning the optics. This is usually a simple but tedious task. Once a smear is gone, the next one appears. Therefore, a larger supply of fresh clean and lint-less wipes is essential. As cleaning agents, I use window cleaner, ethanol (ethyl alcohol, 94%) and isopropanol (isopropyl alcohol, 99,9%). The latter two should be available in any well-stocked pharmacy or drug store. See the tools section to read which fluid fares better and what not to use to clean a lens.
You should start getting rid of any particles left on the lens surface by using an air blower. Then softly patten the lens with a cleaner-infused wipe to remove particles that survived the blow. In the next step, you can very carefully wipe the surface from one side to the other two to three times, using a fresh, cleaner-infused wipe every time. For the last wipe, start at the center of the lens and wipe outwards in a spiral motion. After that, quickly grab a fresh but dry wipe and finish the surface, removing any leftover fluid. This method has proven to be the best for me to essentially avoid any residue on the lens.
Getting rid of dust
The last step in the cleaning process is getting rid of dust. The only problem with dust is, that it’s everywhere. Dust from your cleaning equipment tend to stick to glass and the matte painted metal parts inside the lens. Setting a piece aside for one minute usually leaves enough time for new dust particles to settle on it. Therefore, lintless dry wipes, an air blower, lens caps and small, closed containers are very helpful. A clean desk and patience are, too. I wouldn’t recommend using brushes, as those have to be kept really, really clean and grease-free which tends to be rather annoying. When the whole process is finished, check your lens with the help of a flashlight or any bright source of light held at an angle and admire your work.
When done reading here, have a look in the tools section for recommended and discouraged tools and cleaning agents. I’ve had my share of bad repairs and there’s little reason for you to repeat my mistakes.