Hello MEPER, hello everybody,
Schneideritis, and not "schneider
titis"
is like Richard Haw explains it very well, degradation of the canada balsam (or other material) that cements 2 elements (or more) of an optic.
Why "Schneideritis" ? Because a lot of german Schneider lenses (but also other brands), large format lenses (Super Angulon, Symmar,...) or enlargement lenses (Componon, Comparon,...) have or had this "problem" that seems more annoying (appearance) than a real problem...