Re: Breakthrough Dob

Then you still have to capture the entire cone before it hits the smaller secondary...and will result in a longer scope.  A Barlow will be heavier than a flat secondary as it has at least two elements, let alone the cost of making one that big.
 

--- On Wed, 9/30/09, John R Pierce <pierce@No-Spam> wrote:

From: John R Pierce <pierce@No-Spam>
Subject: Re: [TAC] Breakthrough Dob
To: "TAC mailing list" <tac@No-Spam>
Date: Wednesday, September 30, 2009, 7:46 AM

Alvin Huey wrote:
>
>     Im my personl opinion, I think it is worth it for larger scopes we
>     don't want the eyepiece to be too low for the average observer.     For 18" f/3.6 is good.  f/3.3 is practical for 24" and larger
>     scopes.  Perhaps a 30" f/2.8, but you'll be looking at a 8-9"
>     secondary!  That is the short axis!  The long is probably about
>     13" long.  That's one big honkin secondary that will require a
>     massive spider to hold that thing nice and steady.  And the upper
>     cage will be pretty heavy.  Imagine having a equivalent of a 10"
>     primary up in the upper cage.
>     

This is probably heresy, but what about putting the equivalent of a barlow lens in FRONT of a smaller secondary?

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