Lens repair Carl Zeiss Jena 28-85 II / 4-5

[Nahre]

Hello, A friend gave me a 28-85 Jena II /4-5 lens. I have repaired many lenses. Starting at 80mm down to wide angle focusing changes and loses sharpness at infinity in great extent. I dismounted the all the (3-4) back elements. There might be something wrong about the elements. So I need the lens scheme. I whish there is somebody to help me. Thanks, Erhan

 

[AgX]

I am not aware of Carl Zeiss Jena ever making a zoom lens of that focal range.

However there are such Carl Zeiss zoom lenses (Vario-Sonnar 28-85mm). Be aware of the existence of two different Zeiss companies in both parts of Germany.


There are parfocal zoom lenses that keep focus during zooming once focused correctly.

The early zoom lenses were built up to the varifocal principle and do not keep focus.


May that be the reason?

 

[Jeff L]

It might be one of the Japanese made CZJ. Can't remember who made them.

 

[John Koehrer]

With many zooms there are adjustments for tele and wide.
Usually one is at the lens mount and can be a simple twist mount. Usually locked in place with a couple of set screws. Others may use shims.
The front can be as simple as adjusting the front element/group.