In article <4cv5ri$d1v@newsbf02.news.aol.com>, footlr@aol.com says...

>I purchashed a used Nikon 75-150 series zoom in mint condition. I
>noticed, however, some extremely small bubbles behind the front >element. (..) I took the lens to a repair shop and the guy
>said it was just a defect in the glass itself and not to worry about >it, that it wouldn't affect the image quality. (...) By the
>way, I took two test rolls of Velvia and looked at them under a loupe >and the images are tack shop.

Minor faults like dust inside a lens, a bubble or two, even a light
layer of haze, a small amount of fungus, mars in the coating, or a
hairline scratch in the glass have so little practical effect on a
lens image that they can be forgotten (unless you are like me, a
mint-nut;-). The reason this is true is easy to figure out: the defect
occupies such a small percentage of the lens area that it cannot affect
more than a tiny percentage of the light passing through the lens. Even
if the defect were great enough to cause light scatter at a level of,
say, 5 stops below the average exposure, it would not register on most
films. A deep and extended scratch, a fingerprint, considerable haze, a
lot of hairline scratches all over a lens surface are things that would
show up in images under some circumstances, but not all. Also, visible
lens defects mostly affect the contrast and brilliance of a lens, not
its sharpness.
Hope This Helps