Manual Focus Lenses Forum

stevemark · Joined: 29 Apr 2011 Posts: 5303 Location: Switzerland

Abot 15 years ago I got a CZJ Biotar 2/58mm "pre-set" (1955). The lens barrel was quite OK, but the lens was fogged and the focusing mechanism completely blocked (no way to move it at all). In addition, the aperture was defective and the aperture blades dislocated. An early trial to repairthe lens was unsuccessful, and therefore I leftit on a shelf for years to come.

A few days ago I had some spare time, and looking at Richard Haws repair infos I decided to give it another try.

REMOVAL OF FRONT LENS GROUP

First thing to remove is the front ring/ name plate:

Then we can remove the entire front group:

It's quite obvious that there's something wrong with the aperture blades:

Once the front group is removed, we can unscrew the retainer ring; then the front lens will come out, and both the front lens as well as the inner doublet can be cleaned. Be careful though since these early inner coatings are pretty sensitive and can easily be damaged.

stevemark · Joined: 29 Apr 2011 Posts: 5303 Location: Switzerland

REMOVING THE REAR LENS GROUP

Now let's remove the rear lens group. We start with unscrewing the rear lens - that's a bit tricky since using a lens spanner and turning the outermost retainer ring (as shown here) does NOT unscrew the rear lens element:

What you have to do instead is to look deep into the gap between the lens group and the outer barrel. Down there you'll find a retainer ring that holds the outermost rear lens in position. Remove it:

Once this ring is removed, you can take out the rear lens:

Now the trickiest part of the entire lens cleaning / repair procedure - separating the focusing unit from the lens / aperture.
Lokking into the gap again, you'll find another retainer ring. It's not easily accessible, and unscrewing it originally would have required a special Zeiss tool. However I managed to unscrew this retainer ring by using two small screwdrivers (it's impossible to get into the gap with an ordinary lens spanner tool):

Once the ring has been loosened, we can separate the two halves of the lens.
Be aware that - for time being - the retainer ring we just have unscrewd CANNOT be taken out of the focusing unit (left part in the image):

There's another ring (a distance ring) on the second part. Don't loose or misplace it ... it has to be there to insure the correct infinity setting:

Now we can remove the inner doublet of the front group:

stevemark · Joined: 29 Apr 2011 Posts: 5303 Location: Switzerland

CLEANING / REPAIRING THE APERTURE MECHANISM

First the screw limiting the movement of the aperture ring has to removed:

Then this retainer ring must come off:

After removal of the above ring, the two parts separate:

Without further ado the left part in the upper image (the aperture pre-set mechanism) can be separated into two parts - be VERY careful not to loose the four springs shown here:

Now let's dismantle the aperture itself. Remove this little screw:

On the other side you'll find an empty hole - that's OK (here was the screw shown in the first image above)!

Now we can remove the movable ring of the aperture mechanism:

Obviously the aperture itself is pretty damaged; some blades are bent:

The blades are sticking together; there's old grease all over the place:

Finally we can unscrew the aperture mechanism:

There are twelve aperture blades - be aware that they are NOT symmetrical, and that they MUST be re-assembled in the correct way! I have cleaned them first with water / detergent, and then with acetone. Then the bent blades were straightened as good as possible.

After cleaning everything thoroughly, the re-assembling starts. Inserting the first eight blades is quite easy:

Inserting the last four blades is abit tricky - but less difficult than expected. After inserting the movable aperture ring it should look as follows:

Now we can secure the movable aperture ring with this spring:

The spring is in place, and the the aperture mechanism is repaired:

It looks really beautiful now - and it works flawlessly!

stevemark · Joined: 29 Apr 2011 Posts: 5303 Location: Switzerland

CLEAINING THE FOCUSING MECHANISM

At first I didn't know how separate the two parts of the focusing thread since they were completely blocked / locked at the infinity position.

I thought of using some pliers, but that probably would have damaged at least the outer surface. Finally I tried the chemical path - and it worked: Soaking the entire focusing for a few minutes in acetone resulted in the partial dissolution of the greas / dirt inside the focusing thread, and the two parts were moving again (albeit with difficulty). To separate the threads, first this screw has to be removed:

Be VERY careful when separating the TREE parts of the mechanism (two threads and the third part). All three parts MUST come together in the correct way when re-assembling the mechanism !! I messed it up since those Japanese lenses I had serviced before did have only two parts (the two threads) which must be in the correct position ...

Cleaning the three parts (with four threads on them) was laborious. The old Zeiss grease was pretty sticky, and didn't even come off using acetone and a toothbrush! I finally was able to clean them reasonably well by first using hot water & lots of houshold detergent and a toothbrush, then rinsing / brushing them with acetone, and repeating the procedure. Once more or less clean, the threads were re-lubricated with tiny (!) amounts of Losimol 33B, a grease with low viscosity specially designed for manual focus lenses.

Re-assembling was pretty straightforward - do everything in reverse order Wink

S