Re: ATM Re: Aplanats II via troublesome Juno X-mailer

[Douglas Braun <doug@dougbraun.com>]

Hello,

Perhaps this is sort of a naive question..

By "astigmatism", do we really mean "off-axis astigmatism"?  I do not see
how any properly built and collimated scope could have
astigmatism in the center of the field (except for off-axis designs).

Doug Braun

At 09:55 PM 12/17/02 -0800, John Swenson wrote:

>The Lurie Houghton design has essentially zero coma, zero spherical aberation and an almost perfectly flat field, it does have a little astigmatism. The basic geometry is a newtonian with spherical primary and a corrector right before the secondary (the secondary is usually attached to the corrector). The corrector consists of two weak lenses that are NOT achromats, the same glass type can be used for both lenses.