I'm forever blowing bubbles

[P3D Peter Abrahams <telscope@xxxxxxxxxx>]

> tiny air bubbles in the lenses of two of the viewers.
This sounded to me like tiny air bubbles in the glass, not decementing,
although all the advice on recementing was correct and useful.  These
bubbles are found in almost all antique lenses, and it is astonishing how
minute the effect is.  Many early telescopes give outstanding test results
with more than a few small bubbles in the objective, Bubbles in an ocular
will have no effect unless there is a focal plane in the ocular, a lens or
reticle or bubble there will be visible.  A tiny amount of diffraction
causes a tiny loss of contrast, thats about all.  If the area of the bubbles
starts to get to more than a few percent of the area of the lens, like in a
microscope objective, then it's a problem.
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  Peter Abrahams    telscope@xxxxxxxxxx
the history of the telescope, the microscope,
   and the prism binocular


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