Re: [ATM] Looking for information on a telescope design

["Scott Milligan" <starzkey@charter.net>]

Vlad wrote:

Linear field size is irrelevant for the principle; incoming ray angle from
the secondary to any off-axis point in the final image of the Mersenne will
be 1/k times larger than the incoming angle at the primary.

Ok, that is a consequence of the secondary mirror's magnification, but my
point was simply to consider only the refractor back-end for a moment,
whereupon it seems obvious that a fixed linear field size can only accept
light from a fixed angular field in its collimated object space.  If we
admit that the refractor field and aperture stops remain fully filled in any
well-optimized Mersenne configuration, then whatever off-axis aberrations
the refractor contributes are only determined by the aberrations residual in
the refractor design alone, and are not influenced at all by the presence of
the Mersenne front end.  Of course this argument ignores the possibility for
the existence of induced aberrations, but I think this must be counted as
negligible, given the small incidence angles involved, and also given the
fact that a Mersenne front end corrects all aberrations to third order
except field curvature.  From this standpoint, the sole impact of the
secondary magnification is to reduce the angular field of view in the sky
that is projected onto a given linear field size, with field curvature being
the only aberration that is aggravated in combination.

Scott
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