I didn't have any qualms about that because I cheated. I knew what the
outcome would be. Sticking a piece of tape on the front element is no
different than putting a big old secondary mirror in the middle of the
correcting lens of your catadioptric mirror lens. All it does is block
some of the light and cause a bit of extra diffraction around the edges
of the obstruction. The diffraction scatters a bit of light and can
reduce contrast but you won't notice it unless the obstruction is really
large. The reason you're unlikely to see it is that the perimeter of
your lens cells and filter threads, etc. are also diffracting surfaces
so, percentage wise, that piece of tape doesn't count for much. So,
it's OK to whack the front element with a ball pien hammer. Just
remember to fill in the chip with some black india ink.
People who go bonkers over dust specs on or in the lens need to find
something else to fret about.
Chuck Norcutt
Moose wrote:
I
> think it may have been Chuck who took images with and without a big
> piece of black tape on the front of a lens. You just couldn't see the
> difference in the images.
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