Re: [ATM] Small Dob truss question

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

John Sherman wrote:
>> My question... I'm curious why the traditional dob truss has the 
>> paired tubes meeting at the top ring
> 
> Because usually the mirror box is square and the top cage is round.

Ah, good point.

I should have mentioned that my 8" travel scope has a square secondary 
cage.  Actually it was less work to build than a round one, IMO.  I 
think my 13" will have a similar form.

An advantage of a square cage is that the inside of it is shadowed by 
the front baffle (and a back baffle if you use one), and it looks 
darker to an eyepiece.  That improves contrast.

	Mike Lockwood

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