> Just curious, have the folks on this list checked to see if their
lenses have
> accumulated dust? Do you feel that this type of accumulation has no
effect
> on image quality? Do you ever get the lens professionally cleaned
> internally, and if so, when? Do you routinely check new lenses for
dust like
> this and return them if it is present?
Of course, dust in the lens degrades image quality. However, because
the dust isn't at the focal plane, it won't show up in your image. If
you ever take pictures at a zoo with a fast lens or a telephoto lens,
you'll notice that you can shoot pictures through cage bars without the
bars appearing in the images. Of course, the bars are there, and
blocking light from reaching your film--but if they're very out-of-focus
they essentially disappear. The same thing happens to dust in the
lens--it's typically so out of focus that the blur is spread across the
entire image.
You mentioned that you're using a macro lens, which changes some of
this. If you're focusing on something very close to the lens, and using
a very small aperature, it's possible that the depth of field will
extend close enough to the front of the lens to make some relic of the
internal dust visible in the image. You'll probably never notice it,
though.
FWIW, I can see dust in a couple of my lenses, but never noticed it in
my photos. I've never gotten the inner-workings cleaned.
Tony Northrup
http://www.northrup.org/photos/
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