need help fixing Minolta Apo 200mm 2.8

kiddo · Joined: 29 Jun 2018 Posts: 1146

I bought this lens cheap for having issues that I've thought I could deal with ,basically fungus on the inner elements . I've tested the lenses with 2 adapters and it won't reach infinity, in fact it would only reach up to about 8 meters far away. I really need this lens for my daughter's graduation, so it's about time to try again after leaving it unattended for a long while. Some time ago, I've tried removing front name plate ring , the thin one. The issue is that when I'm trying to unscrew it, would only unscrew a little bit and when it turns, it will do it with the whole front group together (I can see optics moving inside the barrel). So I need help to see what would be the best option to approach this lens , other than the mentioneed before. I did apply acetone all around the name plate ring on top and bottom next to the optic, but no luck so far.

kiddo · Joined: 29 Jun 2018 Posts: 1146

Ok ,I finally figured out and it wasn't that hard .
First the rubber ring from the hood needs to be removed, after release a black outer ring from the top of the hood (where the rubber ring was seated on). This will allow to remove the hood unscrewing it to the rear. Once the hood removed, there's a tiny screw that holds in place the whole front group from the outside ,after this is piece of cake. That tiny screw is the one in charge to hold the front group in place and to allow adjustment of the infinity . I still have no clue how the top side of the lens is connected to the rear side, in my lens there's a little wobble between these two parts , I think they are connected just next to the rear mount

RokkorDoctor · Expire: 2025-05-01

You mention fungus on the inner elements. Minolta APO designated lenses from that era usually have a fluorite (calcium fluoride) element in the front group, protected by glass elements on either side. You need to be very careful with fluorite elements; they are far more easily damaged compared to optical glass.

kiddo · Joined: 29 Jun 2018 Posts: 1146

Thank you , there were few fungus spots under first front element and last one from the front group, close to the diaphragm, some more on the edges ,it cleaned up very well . I avoided to open more than really necessary .
The fluorite element could be the second one? I understand the front group has 4 elements (2+2 cemented?)
Some very small spots have remained where the fungus affected coatings , but otherwise I'm really happy the optics are much better right now and it will reach infinity.
It still bother me the little wobble between the front part of the lens and the rear one next to the mount , I've checked the screws from the mount and they're all tighten. This lens it had some thread locker between the elements, but not at all comparable to yashica ML 50mm 1.4 which finally I was able to open after leaving inside the freezer for couple of days. That lens had a lot of red loctite type thread locker, the most that any lens could have, I'm not sure if Zeiss c/y might be the same , but I guess so.

stevemark · Joined: 29 Apr 2011 Posts: 3771 Location: Switzerland

kiddo · Joined: 29 Jun 2018 Posts: 1146

Steve, can you remove the whole front group from the lens? is the 300 mm lens opening the same as the 200 mm apo for the front group? at least the 200 apo is very easy to access, my lens also has got a good bump at some time

stevemark · Joined: 29 Apr 2011 Posts: 3771 Location: Switzerland

No, I can't.

If I remove the black rubber front ring, there's no screw to be found under it. There is one at the base of the large front part, and removing it doesn't "free" the front part or the sunshade.

My own 2.8/200 APO currently is used by a friend, so I can't compare the construction of the MinAF 2.8/200 APO and the MinAF 2.8/300 APO right now ...

S

RokkorDoctor · Expire: 2025-05-01

kiddo · Joined: 29 Jun 2018 Posts: 1146