Rokinon Automatic MC 135mm f/2.8

Initial condition

I got this lens in the mail in a lot of 7 as-is lenses, so I wasn't sure what to expect. This one looked interesting, as it was an older prime (so maybe a little easier to work on) and the glass looked nice and clean. It has a lot of obvious wear marks, but the main issue was clearly the grease. The aperture blades had big oil splotches on them and the aperture was quite sticky to open back up.

Removing the Glass

The first thing, of course, is to try to figure out how it comes apart. Removing the mount was fast and easy, after which I could easily unscrew the rear group. So far so good.

Next up, I took off the rubber grips and unscrewed the front group (don't unscrew the front retaining ring, the whole assembly will unscrew with the seam hidden by the front rubber grip). For the next group, my spanner didn't fit, so I used a small screwdrivers and got it out just fine -- the holes go all the way through the mount so it's pretty easy to do. 

With all the glass removed, I could be a lot less careful about touching things. After all, I'm about to clean everything so at this point it's fine if it gets dirty. With all the grease seepage all over the insides, I'm probably not going to make anything worse! The photo jumps ahead a bit... 

Disassembly of the Macro Helicoid

The dual-action focus (main and macro) leads to an interesting mechanism to take apart. I unscrewed the big screw that serves as a hard stop as well as the three set screws around the barrel as well. Don't remove the top two screws for the macro stop! It's a pain to put it back on, I think it's easier to just take the pin out of the macro ring. There is a relatively big hole in the main focusing ring under the grip -- this is used to unscrew the brass pin used as a far-stop in the macro focusing ring. The main focusing ring should be basically free turning at this point and you can 'hunt' for the brass pin pretty easily.With the brass pin removed, I could easily just unscrew the front macro focusing ring and slide off the main focusing ring as well. The extent of how gross the grease was suddenly became clear. Old, grey, chunky, nasty grease and gooped on like crazy. That will change.

Disassembly of the Main Helicoid

Looking a the back of the lens, the aperture stop indicator ring (with the red dot) has three set screws holding it in place. Off it comes, watching carefully for the ball bearing! Got lucky -- it's on the top as the lens points down, so it stayed in place. May as well remove that ring too, it's going to need cleaning! I took out the two brass L-brackets on the sides of the aperture, this is what keeps the elements moving forward and back instead of just rotating, but also serves as a stop when it gets to the front of the lens.With those removed, I just 'focused' the inner assembly out the front of the lens. The aperture setting lever needed a little coaxing at one point but no big deal.

Removing the Aperture

The whole point of all this was to clean the aperture, right? Time to get it out. I spent a long time here trying to figure it out... The inner helicoids (with different threads) are two pieces that are screwed together. They were seriously locked together and it took a lot of force to get them apart. Once that was done, the retaining ring on the aperture unscrews easily and the blades and mechanism all pop out.Into the ultrasonic jewelry cleaner with you!

Final Disassembly

I wasn't going to go this far and not clean and re-grease every moving surface. So I took apart the aperture setting ring and the main focusing barrel outer helicoid pieces too. A lot of cotton swabs and paper towels to take the bulk of the old grease off, then they all went into the ultrasonic cleaner too.


Absolutely every part from the rubber grips to the aperture blades with the exception of the glass went through the ultrasonic cleaner and manual cleaning. Everything was as shiny and pretty as I could make it. Time to reverse every step!Putting the aperture back together wasn't too hard with it clean. It was kind of fun. I didn't care about minor fingerprints on the blades and just did it with my fingers. I got some cotton gloves for handling glass but they don't fit too well and would have been very hard to do this with. Maybe a plastic tweezers would have been best but I didn't have one right in front of me.With very light grease applied (I used HELIMAX-XP which is designed specifically for low-seepage in optical helicoids) almost everything goes back together smoothly except the main focusing helicoid. For some reason it is really hard to get back in correctly. The easiest way to get the macro focusing ring back on was to just put the main ring at infinity (closest to the mount) and then try various orientations until the ring screwed fully on --  the centerline of the focus indicator will be between the "O" of MACRO and the "->" when fully screwed in.

Aperture Blades

Aperture Blades

Only the last one is difficult to get in...

Operation on a K-1

This was the first time I've used an original K-mount lens on a Pentax DSLR. At first I thought it wasn't stopping down because it didn't have the A contacts, but it does. It just doesn't have the extra mount ring to read the current aperture setting that was removed on version 2 of the KAF mount (some people call this the "crippled" mount). This hasn't been on modern K mounts for a long time, but I find it works just fine without.The DSLR is clever enough to realize that metering with the aperture open (default state with the lens mounted) won't help, so you don't get any metering info. Unless, of course, you use that friendly Pentax green button. It actuates the aperture lever to perform stop-down metering! The camera still doesn't know what f-stop you've set the lens to (because of the missing mount ring) but it is able to see how much light there will be when you take the shot. After metering, you should be able to adjust your exposure triangle without need of more metering until the light changes, but it's super fast and easy to have the camera re-check which can be handy particularly for spot metering different areas.

Full Frame

Full Frame

Looks at home on the K-1.

Powered by SmugMug Owner Log In