Optical issues with changing rear cells?

[Richard Raymond]

There was a thread about damaged Fuji lenses a while back. One of the suggestions was to use the front cell of the 125mm lens and the rear cell of the 135mm lens. What are the optical issues/problems with doing this? If the lens "works" then is it just that the focal length has changed but everything else is fine?
Thanks for considering this.
Ric

[Gene McCluney]

I don't think it is quite that simple. In "convertable" design lenses, the optical cells are "designed" to interchange and work with various combinations, or alone. In modern Plasmat style lenses, while these designs do stem from "convertable" designs, they have been modified, to perform "best" when used at the factory shipped combination. In other words, they are not "identical" front and back. Putting a rear group from one focal length with the front group from another focal length..both from lenses that were not designed to be "convertable" will probably lead to reduced sharpness, or other undercorrection.

[Glenn Thoreson]

I don't consider it wise to mix cells from identical lenses. I don't know what your idea would produce. A nice experiment, perhaps.