"Two Major Issues with this Lens that are Expensive Repairs"

In this guide, I am referring to the original Vintage model Minolta Maxxum AF50 Macro released in 1985. I have over the past few years come across many of these highly desireable Macro lenses. This lens offers a nice compromise in price when compared to the Minolta Maxxum 100mm f/2.8 Macro, with no loss in 1:1 image reproduction, image quality or aperture speed. The major difference between the two appears to be the working distance between lens and subject, with the 50mm having the shorter distance by a factor of two.

The overall build of this lens is solid, but internally, there is a design Achilles Heel just waiting to turn the lens into an expensive paperweight. Of the many I have inspected, only a few have been offered for resale in my listings. Those were of excellent quality showing no sign of iminent disaster. The rest I either returned to their owner or refused outright to accept as stock for my little ebay thing.

You see, when Minolta engineered this very complex lens, they included a thin metal tape band about 1 cm wide on the outside of the extension tube assembly in order to create an internal "dust seal". This seal is located at the front end of the lens, beneath the cosmetic outer skin, just posterior to the focusing ring. A good idea, but unfortunately the band is affixed to the extension tube assembly with some pretty nasty adhesive which appears to break down over time. It seems that with use and as these lenses age, the likelihood of this problem increases.

Internally, the lenses' extension tubes articulate with one another via a complex system of bushings and grooves that through their movements, extend and retract the tubes to focus and adjust image magnification. Some of these bushings, while on their journey back and forth through their grooves, pass under the metal band and over time pick up small bits of this adhesive. Over time and with use, the adhesive works its way deeper into the lens from one extension tube to the next until as many as all three tubes get a build up of this sticky mess at various points along their surfaces. This creates inadvertant internal friction, with contact and wear points between the extension tubes. The end result is hesitant, rough or very stiff focusing movement. In the extreme case, the camera AF motor can no longer focus the lens. Does your Macro lens do this?

 I would be hesitant to put a stiff focusing AF50 Macro lens on my camera body and try to use it repeatedly. That heavy of a load on the AF motor can not be healthy for it.

The only option at this point is to open up the lens and remove the metal band, all of the remaining adhesive with a solvent, and then clean any glue residue off each of the extension tubes. Not a project for the faint of heart to say the least. Not a project to be undertaken without a repair manual or instruction on the first attempt, either. Like all macro lenses, the design of the AF50 Macro is inherently complex and care must be taken throughout the procedure to ensure a useable lens is the end result when reassembly of the project is complete. It is not an impossible undertaking - I have been able to successfully repair this issue in the AF50 Macro, but there are a few fatal errors that an inexperienced lens disassembly can produce. As an aside, if you are looking at an AF50 Macro in my listings, if I have refurbished or repaired it in anyway, trust that I will make a note of this fact in the listing. It may actually be to the buyers' advantage to purchase a repaired AF50 Macro so that you can be confident that the problem doesn't develop in the future. In my experience, more than half the AF50 Macros that I have inspect have had this problem to some degree. Lenses that appeared to see the most use usually had a more significant stiff-focus problem. Be sure to ask the seller whether the focus ring turns smoothly and easily in any AF50 Macro Lens auction you are bidding on! You could end up stuck with a useless or very poor performing lens if you are not careful. The "Camera Shop" labor involved in repairing the lens would likely double (or more) your winning bid price. May as well buy a new one at that cost.

The other issue that can affect this lens is the bane of all lenses, the oily aperture. Normally, the thin, lightweight aperture blades are clean and dry and slide easily over one another. Oil shows up on the aperture blades after the lens has been left in the heat of the sun, or a locked up car on a very hot day. Increased exposure to extreme heat exacerbates the likelihood and/or severity of the problem. Grease that lubricates the focus gear warms up and liquifies. Over time, the oil seeps its way centrally into the aperture mechanism.  As the blades open and close with regular use, oil is pulled further onto the aperture blades. There, because of the viscosity of the oil, blade movement is impeded. Initially, your lens aperture will be sluggish. This can affect exposure if the lens is unable to stop down in the short interval prior to shutter release. Eventually, as the problem evolves and more oil builds on the blades, they will stick in the wide open (f/2.8) position, causing overexposed images on every photo. The lens is now pretty much useless. 

To check a lens for this problem, you can inspect the lens aperture under bright light. If areas of the aperture appear wet or darker or shiny in comparison to the greyish matte color of a normal aperture, or a multipoint star or petal-like pattern are apparent, chances are you are seeing oil on the blades. Another easy check is to take a toothpick and slide the lens aperture adjuster located on the lens mount. The Adjuster is a metal tab located in a narrow 1" curved slot near the gold contacts at the lens base. The tab is spring loaded and connected to the aperture mechanism. It should snap back smartly if the blades are clean. You can visualize the aperture action while you do this. Compare the action of the questionable lens to one you know has a clean aperture. Any difference in action could indicate a problem.

To repair an oily aperture in an AF50 Macro, further disassembly (beyond removal of the extension tubes) is required and the aperture blades must be cleaned. Again, a very tricky and time consuming venture. Once cleaned, everything has to be properly reassembled. I haven't attempted this yet. It is much easier to simply buy a lens without the problem!

Once again, the bottom line is "ask the seller questions about the item condition" prior to bidding! If you don't get a straight answer, look elsewhere. The AF50 Macro is not a cheap lens, and the potential for getting a used lemon on Ebay or elsewhere is relatively high, so be careful and make sure you are getting a good one. When working as it should, this is an excellent lens. It is super sharp and delivers beautiful 1:1 image reproduction with a nice bokeh and lots of depth of field control. Anyone interested in macro photography would appreciate this lens. But when a problem arises like one of the two I've mentioned, you are looking at an expensive repair in a camera shop, or replacement at significant cost. Asking a few simple questions prior to purchase can save you a world of hurt when your item arrives in the mailbox. If you wish to repair an AF50 Macro that has developed this problem yourself, ensure you have a guide to refer to so that you don't destroy your lens in the process of the repair attempt.