[nebulosity. (Jo)]

Originally Posted by Merlin66

Very nice.
What size disk do you have on the secondary holder?
There's a program called I think "Newt" which calculates the secondary and the spacing....
http://www.dalekeller.net/ATM/newton...t/newtsoft.htm

Thanks Ken, the disks for the secondary holder are 3x50mm. It is a new design I'm trying, it has only one adjustment screw! And is more sturdy and rigid than any secodaries I have made before, I'll post some more pics of it when it's done.

Thanks for the link, I put in my specs and it reckons with a 63mm mirror I'll get a 32% obstruction with a 20.68mm 100% illuminated focal plane. And with a 70mm mirror I'll get a 35% obstruction with a 29.84mm 100% illuminated focal plane.

Which one do you reckon would be best? I will be using APS-C size sensors (24mm) most of the time but might upgrade to full frame later on.

probably going slightly bigger than I need is not a bad idea.

Cheers
Jo