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Coma Corrector Chromatic aberration

Equipment Coma Artifacts
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Gabriel Wiklund avatar
Gabriel Wiklund avatar
Hello,

My images suffer from chromatic aberration with 2 different cameras and Newtonian scopes even when imaging 65° above the horizon.

 I have been using the Explore Scientific HR Coma Corrector so since that's the only lens in my system it must be the cause.

Does anyone here have any recommendations for a Coma Corrector that can handle F3.4 and that does not suffer from CA?

Clear skies!
Gabriel
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andrea tasselli avatar
andrea tasselli avatar
That would be odd, LCA is usually associated with tilted optics hence one might be lead to infer that the issue isn't with the CC per se.  The TS 4 -element CC works brilliantly @ f/4 but so do others as well. It all depends on the depth of your wallet.
Gabriel Wiklund avatar
Gabriel Wiklund avatar
andrea tasselli:
That would be odd, LCA is usually associated with tilted optics hence one might be lead to infer that the issue isn't with the CC per se.  The TS 4 -element CC works brilliantly @ f/4 but so do others as well. It all depends on the depth of your wallet.

Thank you for pointing this out, my wallet is not deep at the moment so it would be great if the problem could be solved without a new CC. 
So if i understand this correctly if the CC is tilted, that could cause CA?
andrea tasselli avatar
andrea tasselli avatar
Something is tilted but your problem is that imaging system is giving you poor correction and that is exacerbated by the very high image scale. Hard to say but one test I'd do is to image one brightish stars with the Nikon without the CC in place (is that modded? I expect not) near the zenith (few seconds worth of single shots, then stack them up). Look to see what the pattern is like. Is the center correction good, is the coma pattern radially symmetric? Then image again at different altitudes but above 60 degrees to see if you are collimated at different altitudes. And see whether the Nikon is to be excluded. Mind you, it might still turn out that your HR CC  is a poor copy with a wedged element but optics is a hard science…
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Gabriel Wiklund avatar
Gabriel Wiklund avatar
andrea tasselli:
Something is tilted but your problem is that imaging system is giving you poor correction and that is exacerbated by the very high image scale. Hard to say but one test I'd do is to image one brightish stars with the Nikon without the CC in place (is that modded? I expect not) near the zenith (few seconds worth of single shots, then stack them up). Look to see what the pattern is like. Is the center correction good, is the coma pattern radially symmetric? Then image again at different altitudes but above 60 degrees to see if you are collimated at different altitudes. And see whether the Nikon is to be excluded. Mind you, it might still turn out that your HR CC  is a poor copy with a wedged element but optics is a hard science...

Thank you, informative!

The Nikon is unmodified, but i had the same problem with CA even with the 200PDS and 533MC Pro. However i realize at this moment that i did not have CA when i used my 200PDS and a planetary camera (without the ES HRCC) so it seems the HRCC is the problem. I did drop the ES HRCC by accident once when doing visual (had not tried imaging yet) so pherhaps that is the cause.