Thank you Robert,
When I thought it over again, I realized that for instance a F/8 scope with off-axis mirror, is in fact part of a paraboloid with something like F/3.4 and that should introduce a tremendous amount off coma. I read some tests on the ITE site of recent introduced off-axis parabolic mirrors (made by DMG), and there the coma was not mentioned. I do not know, but it might be the case that these ITE scopes do not have a flat secondary to correct for the coma (or that the primary is compensated somehow)?
My own scope is a MN61 (20% central obstruction), and I experienced with blocking more of the primary and I feel it rather amazing what a difference that makes. Differences between 20 and 25 % are so good noticeble, that I am really wondering what the effect of 0% obstruction would be for the same scope. So, I become interested in the area where I am starting to investigate for a simple and elegant solution to avoid the obstruction.

• RE: RE: RE: Off-axis parabolic mirrors - bobmay - July 19, 2000 - 22:56 UTC
• RE: RE: RE: Off-axis parabolic mirrors - Steve Fejes jsfejes@swva.net - July 20, 2000 - 02:03 UTC