Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
07-28-2011, 12:58 PM   #1
Inactive Account

Join Date: Jul 2011
Location: Dallas
Posts: 4
putting back together pentax-m 50mm 1:2

I thought I'd be cool and take the lens apart to clean it because I thought it needed it. Well It came off easy enough, but I'm too stupid and don't know how to put it back together. Is there any way I can get a sort of tutorial online? can anyone help?

07-28-2011, 01:02 PM   #2
Veteran Member

Join Date: Sep 2010
Location: Canberra
Photos: Gallery | Albums
Posts: 739
This thread, which has links to some other threads, might help:

Or this
07-28-2011, 01:11 PM   #3
Veteran Member
Docrwm's Avatar

Join Date: Sep 2010
Location: Somewhere in the Southern US
Photos: Gallery | Albums
Posts: 12,244
If you decide you can't do it there is a guy named Eric that repairs and CLAs lenses that does a great job by all accounts (and he is reasonable too). Just search here for Eric and repair.
07-28-2011, 02:32 PM   #4
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 5,742
I am betting that you unscrewed the focusing helix. Large aluminum threads, greased? There should be a warning label, don't unscrew this. The large threads have (I think) three starting points. It takes a lot of patience to get the right one. When you have the wrong entry point, the rest of the parts don't line up in the right place.

The main reason for doing that is, your M50/2 doesn't focus any more. A drop or whack causes focus to stick. Often someone strong tries to force it, and the grip peels off too. Lots of these jammed lenses on eBay. The problem is not that obvious, and you may not have fixed it yet. You have to start at the front. Unscrew the trim ring with the lettering on it, or if the filter threads were damaged in the accident, pop it off; it's plastic and has little slots in it 180 degrees apart. If you unscrew the three screws holding the brass washer, you can remove the front lens group entirely. There are three more screws holding the focus ring on. Remove those and take off the focus ring. Your lens should look kind of like the last photo except that's an M50/1.7. The aluminum ring here is the jammed part. It will be tilted off axis, so the ring is not parallel to the parts underneath it. You have to pop it back onto its fine threads. I just look for the low side and pry it back up.

Once that ring turns properly, you can reinstall the focus helix. First screw that aluminum ring all the way tight, then loosen it about 10-15 degrees. In the third photo here, the lens on the right is almost stripped down. One L-shaped copper piece has been removed here. It's called a guide bar, and it keeps the lens moving in and out, not turning as you focus. What I did was remove both guide bars, screw in the focus helix, and see if everything lined up right. That meant reassembling the stuff on the back of the lens. If everything goes on right, you win, and can put together the front. Or try again, trying to rotate the helix 120 degrees each time to get it to start in a new place.

You'll have to reset infinity focus when you get the lens nearly back together. Once you have the mount and back end on, put the front lens group back on. Tighten the aluminum ring again, and back off the same 10-15 degrees. Put the focus ring on with only one screw tight and the orange diamond somewhere close to infinity. Now put the lens on a camera, point at something infinitely far away, and focus until it's clear. Once you get sharp focus on a distant object, loosen the tight screw, rotate the focus ring until the diamond points at the infinity symbol, then tighten all three screws. Put the rest of the lens back together.

These photos are about 5 years old, the last time I did this, so I might be missing something. Filter ring, I skipped that. Anyway, they should show just about everything in an assembled or unassembled state.

Last edited by Just1MoreDave; 07-28-2011 at 02:42 PM.

  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
k-mount, pentax lens, pentax-m 50mm, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Having trouble putting on a Pentax Hand Strap. NecroticSoldier Pentax Camera and Field Accessories 22 04-10-2011 06:46 PM
Going back in time: Pentax A 50mm F1.7 (new purchase!) legacyb4 Pentax SLR Lens Discussion 31 10-29-2008 09:48 PM
Back lens cap for Pentax-M 50mm f/1.7 Timarete Pentax SLR Lens Discussion 2 05-09-2008 09:02 PM
Need some help putting my focusing screen back (the correct way) rhermans Pentax DSLR Discussion 3 07-16-2007 12:32 PM

All times are GMT -7. The time now is 10:31 PM. | See also:, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]