CONTAX Carl Zeiss Tele-Tessar T* 300mm f/4 (MMG) Disassembly – Cleaning Fungus from the Middle Group

This CONTAX Carl Zeiss Tele-Tessar T* 300mm f/4 is a long telephoto lens for the C/Y mount. It weighs about 1.3 kg and takes 82 mm filters. I serviced it in September 2024. This post walks through the disassembly and cleaning, step by step.

When I bought it, the seller wrote that there was fungus on the middle elements, “not enough to affect pictures”. In the seller’s photos, though, looking in from the front, a large petal-shaped patch of fungus was clearly visible in the centre of the lens (the seller described it as being on the middle elements). Fungus does not go away by itself, and it is better removed before it spreads or marks the coating. So the goal of this job was to get to the middle group and clean it.

Here is how the job went.

1. Taking out the front group

To reach the aperture and the middle group, the front group comes out first. On this lens the whole front group comes out of the barrel in one piece, at a threaded joint. You can see its silver ring and black thread as it comes out.

Inside the front group, the front elements (around the first and second elements) are loosened with a fine screwdriver.

There is also a small screw hole on the outside of the barrel, shown here with the tip of a needle. A screw comes out from here.

2. Wiping oil off the aperture blades

With the groups out, the aperture at the bottom of the barrel can be reached. There was oil on the aperture blades, so I wiped it off from the mount side and from the front, using a long stick with lens tissue wrapped around the tip. Oil on the blades can make them sticky and slow, so it is best removed. In the first photo one of the removed groups sits on the right.

3. Checking the middle group against the light

Next I held the middle group, where the fungus was, up to the light and looked through it from two angles. Light shows things on the glass that are hard to see otherwise, such as fungus, haze or dust.

After cleaning, the fungus was gone, and the glass looked clear against the light.

4. From the rear

This is the view from the mount side.

Then I opened the ring inside the rear of the lens with a lens spanner.

5. Back together

The front group went back into the barrel.

And here is the front of the finished lens, with the Tele-Tessar 4/300 and T* markings.

After this service, I listed the lens as CLA’d (cleaned, lubricated and adjusted) in Mint condition, and it was sold.

A seller’s note like “fungus, but it does not affect pictures” is common on old lenses. On many lenses the groups can be taken out and cleaned.
Thank you very much for reading.