Repairing a Meyer-Optik Görlitz Oreston 50mm f/1.8 Lens (2nd Zebra Version)

The Meyer-Optik Görlitz Oreston 50mm f/1.8 lens is a legendary lens. It is famous for its painterly bokeh wide open, and for it sharpness when stopped down. The early versions of this lens have both the aperture and the focus rings in "Zebra" style - this later version has only the aperture ring in (a different) "Zebra" style. This piece was made around 1969.
Usually, for these old lenses the old grease became stiff, making the focusing hard - plus: oil on the aperture blades causes the aperture to get sticky and close either slowly or not at all.

General Recommendations

First, you need tools like a lens spanner and (good!) screw drivers. For cleaning the metal surfaces, I am using cotton swabs and high percentage Isopropyl Alcohol (I got 91%) for all metal surfaces and the glass - and lighter fluid (Zippo) for cleaning the old grease in the helicoids). You also need helicoid grease.

I strongly recommend to take photos of every single step along the way. Whenever I take off a piece, I first try to understand how it was connected and what it did, and then I clean immediately all of its accessible surfaces with alcohol-soaked cotton swabs. 

Disassembly

Here, I show the pictures of the disassembly and cleaning of my Oreston.

It starts with loosening the little screw (below the "O" of "Oreston") - just loosen it, don't take it out. Then you can unscrew the front piece by hand and, with a lens spanner also the front glass piece.

On the back side, removing the three screws lets you take off the back piece and then, the aperture ring (don't loose the little metal ball that comes out - it's for the aperture ring's clicks).

Warning! There are three small grub screws holding the rear glass piece on the left. And it seems like you could take these out to separate the rear glass and to get access to the rear side of the aperture. But don't do it! Don't open these! In fact, these grub screws are used to align the rear optics - and once removed, you will never be able to align the optics again, as this requires special tools.

I set the focus ring to a defined value (I pick infinity) - then I remove the helicoid key.

Careful: Now the helicoid can rotate freely - don't "play" with it, but keep it in its current position.

Before taking out the coarse helicoid, remember where it was (take notes & pictures). Then slowly rotate it out and remember exactly where it became free (this one was cleaned already before I took the picture - yours will likely have old dark, sticky grease on it). 
The helicoid piece also holds the aperture mechanism. If you wanted, you could take out the aperture blades (from the front), clean them (carefully!), and reassemble them. The last step can be difficult and time consuming - that's why I always try to clean the aperture blades in-place. I put lighter fluid on a cotton swab and rotate it around the closed aperture - open and close the aperture - and repeat this 20-40 times (always using new cotton swabs) until it looks clean and moves without resistance. This ususally works very well, and a full disassembly is not needed.

These two screws are setting the limits for the focus ring. Before removing those, I make sure that the focus is still set to infinity. Before unscrewing the fine helicoid, I always test (and take a note) how many turns it could be inserted (i.e. rotated clockwise) until it comes to stop, starting from infinity - and then, how many turns it takes to come out, and at what position it exactly comes out.

Cleaning both helicoids with 91% IPA and/or lighter fluid.

Using small amounts of lube, first insert the fine helicoid (the focus ring) and make sure it sits exactly at the infinity position before you removed it.

And the coarse helicoid too. 

Put back the helicoid key, ...

... the aperture ring (with the ball!), ...

... and the rear piece.

Before assembling the front, you may want to extract the front lens and clean it, if needed.

This lens is finished! While it can't hide its age, it will function for many years with clean glass, a snappy aperture, and smooth focus - and inspire someone to take great pictures! 

More of my lens repair tutorials can be found here.