Stripping and cleaning a Meyer-Optik Gorlitz Domiplan 50mm f/2.8 M42 lens
I bought this lens as ‘for spares or repair’ from eBay a few days ago for £9 as a project to help develop my strip down and clean up skills! When I received it the aperture blades were completely stuck open so that no amount of trying to free it by turning the aperture ring or pressing the actuation pin would work so I pulled it apart and wrote this post as I repaired it. I apologise for the quality of the images – I took these with a compact camera as I did the strip down.
Turns out it is relatively easy to get it apart. I’ll describe the process here but please refer to the pictures above for greater clarity.
- Remove the aperture selection ring by unscrewing the lens nameplate on the front. It may be quite stiff but I found gripping the lens by the body and applying force with the fingers flat on the nameplate enabled me to get enough grip. There is a large spring under the aperture ring which you can also remove as the ring comes free. Note that the thread of this component is plastic so it can be easily cross threaded or worn by being fitted too many times. My advice would be to make sure you take it off once and only fit it once the whole operation is complete.
- Turn the lens over and unscrew the ring round the outside of the lens. Again this will probably be stiff. Once this is off it reveals the workings of the aperture control.
- Remove the three small screws which hold the aperture control assembly onto the lens body. Two of these are located under the bar which moves the aperture but they can be undone with a small watchmakers screwdriver. Be careful because as the control assembly is removed it’s possible for a couple of small springs to fall out. If they don’t I recommend you find them in the lens body and remove them for safekeeping.
- Now the aperture compartment itself is revealed and can be opened by removing the three screws which hold it on. Lift it away to reveal the aperture blades. In my case the blades were covered in oil which was why they wouldn’t move. Note that in the disassembly pictures above the blades aren’t shown because I removed them for cleaning before I took the picture.
- In order to remove the oil from the aperture blades and assembly I dropped them all into a small glass with about 1/2 inch or Isopropyl Alcohol and swirled it all about for a minute or so and then put them through an ultrasonic bath for 3 minutes to give them a final wash. Once the wash finished I put all the items on a piece of tissue for a few minutes and let them air dry.
- At this stage I fitted the aperture assembly back on the lens body and held it in place with one of the screws so it didn’t move about as I reassembled the aperture blades.
- As with any aperture, re-assembly is an exercise in patience. The rules are
- Don’t touch the blades with your fingers – it’s easy to damage them and you could transfer oil from your fingers to the blades
- Add each blade with the small protruding pins sitting in the relevant holes in the aperture assembly. The pin at the end of the blade goes in the outer ring and the pin towards the right angle sits in the inner ring. The photo above shows this.
- As you add each blade you fit it over the last one you fitted. When you get to the last two this becomes tricky because you have to also fit it under the first blade you fitted. It’s particularly fiddly with the last blade.
- Moving the aperture pin with make the rings turn relative to each other and the blades will form the correct O shape, but be careful as a rapid movement will make the blades fly out.
- Once they are all in place you can fit the top of the aperture assembly in place. Remove the screw you used in step 6 to hold the aperture assembly together and fit the top in place. You will need to slightly close the aperture so that the blades don’t get trapped
- In order for the focus helicoid to properly drive the back lens assembly the two small pegs in the camera body need to fit into the two slots in the back lens assembly. These two slots then have the small springs fitted inside them. At this point I must admit I didn’t find a way to get the two springs to stay in place whilst I reassembles the lens – this is something I’m still thinking of a method for and my lens was assembled without them
- To fit the bottom of the lens I found it best to hold it the right way up and drop the rest of the lens in it, making sure that the aperture will close down as the pin is pushed. Once this is working it’s easy to put the lens back on the bench upside down and screw the retaining screws in place.
- Finally, reassemble the front aperture control ring and makers name plate.
The missing screws didn’t seem to be a problem – there is a small amount of play in the lens focusing but not too bad. Once I work out a method of fitting the small springs I’ll amend this post.
Some sample pictures taken with a Domiplan are shown in this post