90/2.8 quality control

["Charles E. Dunlap" <cdunlap@rupture.ucsc.edu>]

Happy New Year to everyone.

For the past month I've been involved in an informative series of exchanges
with B+H camera. I bought a 90/2.8 M lens there in early December. When I
returned home from the trip to New York City I noticed that the coating on
the rear and front elements had three or four little specks in it that
showed up as bright, mirror-like reflections. These defects were in the
coating and did not respond to Dust-Off, a microfiber cloth, or a Lenspen.
I sent the lens back and received a second lens (diff. serial number, but
still 369xxxx). This lens had a couple of the specks on the fron element
and a distorted spot in the coating. The rear element looked ok. I returned
the lens again and the third lens was just fine. The third lens is not in
the ser. #369xxxx batch.

B+H was very good throughout the entire process. They shipped the exchanged
lenses the day that they received my returns and did not protest in the
slightest about the swapping.

It seems that Leica has had a problem with a recent batch of 90/2.8 lenses.
If you're in the market for one, look at the front and rear elements
carefully in reflected light. I was panning the image of a reading lamp or
window across the surface to examine the coatings. I am not convinced that
the specks or small distortions that I saw in the coatings would
necessarily show up in photographs; after all, early Leica lenses often
have bubbles of much larger size in them and these do not effect image
quality. But a coating with flecks in it or a distorted patch does worry
me. Perhaps the coating was not applied properly and will not wear well.
For the cost of a new Leica lens I expect the coatings to have no visible
flaws.

- -Charlie