On Sat, 12 Sep 1998 20:16:43 +0000, "Dana" wrote:

>I have a Canon 28-105 USM that I purchased new about 6 weeks ago. A couple
>of days ago a noticed a mark on the rear glass element of the lens. It's
>about the size of a pin head, white in color, semi-translucent, and in
>certain lighting I can see a blue halo around the white mark. It's
>circular, but not a perfect circle and is definitely on the outer surface of
>the glass. Any ideas what this is? A chip in the coating? fungus? or what?
>
>The lens is under warranty, do I need to have it replaced?

Most likely a spit mark - never blow on a lens, or talk over one,
since spit marks are quite hard to remove from multicoated lens
surfaces... (Try a clean small cotton swab ["Q-Tip"] very lightly
dampened with glass cleaner, alcohol, or lighter fluid if simple
[up-directed!!] breath-and-swab alone does not work - finish with
a clean swab and up-directed fogging breath.) In any case, the
mark will not affect the lens image.