Leica SUMMILUX-M 1:1,4/28 mm ASPH. Notice D'utilisation page 27

CARE TIPS FOR YOUR LENS
Dust on the outer lenses should be removed with a soft hair brush or carefully
using a clean, dry, soft cloth. Micro fiber cloths (available from specialist
retailers) are ideal and can be washed at up to 40°C. To remove marks or
fingerprints, wipe the lens with this cloth starting in the middle and working
towards the edge in a circular motion. Special cleaning cloths for glasses should
not be used as they are impregnated with chemicals that can damage the types
of glass and coatings used.
The bayonet is given an ultra-thin film of grease in the factory to ensure that the
lens can be changed easily, gently and smoothly. In normal use, this is retained
for many years even if the bayonet is occasionally wiped with a clean cloth. If a
substance that dissolves grease is used for cleaning, the grease film must
subsequently be replaced. To do this, coat the bayonet with a tiny amount of
Vaseline with a finger and spread using a clean cloth.
Important: Make sure that the area around the lens identification (7) in the
bayonet fitting is left clear, as otherwise grease residue can accumulate in the
recess and collect more dirt. This could impair the legibility of the code and thus
restrict camera functions on digital M models.
In addition to the type designation, every lens has its "personal" serial number.
Note this number in your documentation for security.
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