Re: [ATM] gregorian considerations

[Mike Lockwood <melockwo@uiuc.edu>]

Doug,

Douglas S Angle wrote:
> Thanks to all that replied to my earlier post about gregorian baffling
> 
> Mike Lockwood wrote:
>>Using the tertiary to direct the light path to the focuser on the top of 
>>the mirror box in itself performs some baffling, because the view of the 
>>sky through the eyepiece is limited to the reflection off the tertiary. 
>>Otherwise, the eyepiece sees the bottom of the mirror box.

> It looks like a great scope.  I hadn't thought of this approach of a 
> tertiary mirror before the primary, and others suggested similar 
> approaches.   It also allows more flexibility in the secondary-to-focus 
> distance.  I can't see that using a tertiary mirror is any different than 
> a baffle of the same dimensions at the same location though.

Thanks, it is a fun scope to use, and performs well.

The tertiary actually allows you to reduce the size of the secondary a 
bit (which confers the advantage of lower obstruction).  There is a 
limit though, as a tertiary that is too large will block light going 
from the primary to the secondary.

The tertiary mirror basically acts like a baffle, but it is slightly 
different.  If the focuser looks into a baffle tube, there can be 
grazing reflections through the baffle.  The mirror box doesn't have 
the grazing reflections.

	Mike Lockwood

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