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Also, I've found that the primary in the Orion Maks are not under sized according to my tests using a laser perpendicular to the meniscus. The light beam hits the primary as soon as it passes the edge and enters the light path. I could not detect any light going past the primary. Just musing.

Tony

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The steeper the curve, the more divergeance it has. Meade makes a point of using an 8" primary on their 7" Mak.

The entrance pupil is the diameter of the corrector, but to field that light does require a primary larger than the corrector.

How much larger is a calculation an optician should be able to provide.

Your laser should not be perpendicular to the corrector's surface, but its beam should be parallel to the tube for On-axis rays. Tilt the laser slightly sideways to simulate off-axis rays.

In my Orion 127 Mak, a laser beam shone into the tube , kept parallel to the tube, hits the edge of the primary mirror well before the beam gets to the edge of the corrector, indicating that the undersized primary significantly vignettes the light from the edge of the corrector. It's difficult to evaluate perfectly, but it appears that the amount of corrector that actually casts its light on the primary mirror is less than 120mm.

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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie


Edited by Starman1 (07/31/05 02:04 PM)

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