[HoutHans]

Can anyone confirm that removing the name ring that surrounds the front element will expose the screws that will allow me to set infinity focus? I have a these lenses that I use for astrophotography but they will not focus to infinity anymore ever since I'm using a clip in filter. Adjusting infinity focus seems a relatively simple way to deal with this, or am I mistaken?

[MossyRocks]

I believe that they are like what you describe. I have had to do that with most of my older lenses (they get real close but not all the way to infinity when checked with a bahtinov mask) and the process is remove the name plate, remove another ring and then you can get at the focus screws. I have done this to my K 35/2, K 30/2.8, A 28/2.8, and A 50/1.2 so I would assume that the K135/2.5 would be the same as would the M50/1.4 since my K lenses that I have done this to are the same and the later A lenses are also that way so I would be surprised if the M was different.

[Not a Number]

Should be the same basic design as almost all prime lenses of the time period.

Under the name ring there should be three or more screws that hold on the filter ring. Remove these and the ring and there should be three or more screws that anchor the focus barrel to the helicoid barrel. Loosen or remove those so you can adjust the helicoid and re-align the infinity mark on the focus barrel. Some lenses have cut-outs on the filter ring so you can get at the focus barrel screws without taking off the filter ring.

[HoutHans]

Great, many thanks for this very helpful information. I'll post a confirmation if this works indeed!

[HoutHans]

This is indeed how it works, first you remove the nameplate ring. I made a small tool from a bit of 50mm PVC pipe I had lying around and fixed some double sided tape to it. The nameplate ring came of easily. To remove the filter ring was a bit more fidly as the three screws for that are underneath the filterring, but that was not too difficult (though I'm happy that I didn't take them out completely and just left them in the filter ring. That provides easy access to the three rings that hold the barrel to the helicoid barrel. Easy peasy. The problem is that I've now found out that my lenses still won't focus to infinity as the clip in filter holder is too high. The rear-most element then touches the frame of the clip in filter. I guess I'll need to send some emails to STC.

[Just1MoreDave]

I think to adjust infinity focus on the K135/2.5, the whole front barrel unscrews. If the lens was vertical and the mount was on the bottom, everything above the focus ring unscrews. You should see the three screws you need to access much like on the 50mm. You also need a longer screwdriver. I haven't had one of these lenses for quite a while, so I am not 100% sure.

[HoutHans]

Thanks, Dave. I'll check it out and report back if it works that way as well.