Quote:
Originally Posted by Steve Pattie
Hmmm. I understand the reason for the flattener, but isn't placing lenses in the light path prone to chromatic abberations. The RC was designed for full field flatness across a large image circle without having to use correctors.
Steve
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Just to reiterate in this, technically the RC design gives a large flat field... flat in the sense that it doesn't suffer from coma (field curvature) BUT only suffers from astigmatism. For science this is fine because without field curvature stars remain in their correct astrometric positions and it doesn't matter if their size (FWHM) changes. A corrector is needed to correct for astigmatism to give what us astrophotographers would consider a flat field in that stars remain uniform in size across the inaging field.