Clean with lens cleaner and paper. First,
don’t forget to blow off the dust with a
blower!
The front and rear lens groups sand-
wiching the aperture are in a “unit
structure” housed in a metal tube. The
lenses facing the outsides of this unit
are hard coated, so it is okay to clean
them, but if you disassemble it, the
lenses on the inside are soft and can be
scratched easily.
Optical diagram of the MD 50mm f1.7 lens.
Pull out the rear lens unit.
