Disassembly – Carl Zeiss Biogon T* 35mm F2 ZM lens

Today I’m disassembling Carl Zeiss 35/2 Biogon T* ZM lens (Leica M mount) to replace helicoid grease.

First step is to separate optical core and focusing frame. You may need to use few drops of acetone to release glue of securing ring, then use spanning wrench to unscrew that ring CCW.

Pull out optical core. Note – there is set of radial shims for precise focusing calibration. Silver bolt should fit the socket of focusing frame when assembling lens back.

Now unscrew thress black bolts that hold textured part of focusing ring, remove that part.

At this step you can also unscrew two black bolts holding brass focusing ring transmission. NOTE: it is important to mark bolts positions on that brass surface for precise focus ring calibraiton.

Flip focusing frame and unscrew four silver bolts from mount ring and remove it.

Then unscrew four black bolts holding focusing ring scale and remove it.

If you look closer, focus ring transmission has darker circles at position where bolts locatet – that is exact position to put them back when assembling.

Now use acetone again to dissolve factory glue holding the focus ring scale, then use spanning wrench to unscrew it CCW.

NOTE: opposite surface of securing ring should be covered with lubricant during assembly.

Remove focus scale ring. There is groove area in the right-bottom – it serves for rotation limting by silver head bolt.

Now unscrew bolts on each brass helicoid guider and remove them. In my sample guider with open middle groove is located at opposite side, and it required slight deformation to make it just a tiny wider to eliminate focusing “lag”, but still narrow enough to easily slide inside its socket without noticeable friction.

At this point you can simply unscrew all three helicoid rings CCW and clean them from old grease. I’m using 99% isopropyl alcohol and soft textile cloth until all surface and thread are perfectly clean.

Now is challenging part of knowing how to assemble these three rings back into correct position.

I’m showing this step without applying grease for more clear view. Note that inner thread is much more thin and requires very soft grease, so rotation of that ring shoul dbe completely efortless.

First locate middle and inner ring like shown on picture. The protruding right pin edge of middle (brass) ring is aligned right next to left edge of helicoid guider socket. Note – the horizontal opening in inner helicoid ring ends there. Catch the inner thread at this point and rotate it CW.

At some rotaiton point left edge of protruding left pin should almost touch the start edge of horizontal opening of inner helicoid ring.

At the end of rotation the right protruding pin should be stopped by right edge of inner helicoid ring horizontal opening.

Now I’ll separately show how to conect middle helicoid ring with outer helicoid ring. Use soft pencil to mark position of right edge of right protruding pin on middle (brass) ring. Connect rings to align that marked line with silver bolt position like pictured below.

Now I’m adding grease to helicoid and assembling it.

Here’s the look of relubricated and assembled three helicoid rings. It’s time to put back brass helicoid guiders and assemble everyhting in a reverse order to steps described above.

Please let me know if you try these steps and have any questions in the process, I’ll be glad to help.

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