Re: [ATM] Ball bearing for triangles,spherical aberration caused bythermal gradient inthemirror :theresults...(long)

["vladimir sacek" <v959@msn.com>]

Peter,

If you meant a single lens coma corrector, it can, but 
with strings attached. I was wondering about the same
question for some time. Turns out, the only lens shape
that can generate enough off opposite coma to significantly
reduce or cancel that of a paraboloid is a positive meniscus,
concave toward mirror. Unfortunately, along with generating
coma, such corrector also generates overcorrection and 
either astigmatism or chromatism. Limit to reduction of coma
w/o introducing more than ~1/8 wave overcorrection seems 
to be ~30%.

An example would be a positive meniscus 80mm in front of the
focal plane, 360mm&240mm radii, 0.5" thick BK7. Chromatism
is very low, and atigmatism is still fairly low. Relaxing the first
radius further reduces coma, but increases chromatism. 
Reducing both radii in proportion also reduces coma, but increases
both spherical and astigmatism.

Obviously, somewhat overcorrected mirrors (hyperboloids) could
take advantage of it to have coma reduced this way somewhat 
more.

Vlad

  Vlad,

  Can coma be corrected in a similar way?

  Peter

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