Re: ATM tube diameter for dob

["Bob May" <bobmay@nethere.com>]

The technical way is to calculate from the FOV that you desire the tube
expansion of the edge of the light cone going to the primary mirror from the
outside world.  An 1 deg. FOV with a 60" tube length gives a 1.04" larger
(1" is close enough) tube than what the primary diameter is.
I'll note that larger increases in the difference also mean that the focuser
needs to be mounted closer to the tube for the same operation or you get a
larger secondary size to fill the focuser with unvignetted light.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net