Resources on the web:
- Mel Bartel's diagonal Calculator
www.bbastrodesigns.com/diagonal.htm
I like this one.
- Newt for the web:
stellafane.org/tm/newt-web/newt-web.html
This is on the Stellarfane site.
- Mike Lockwood's page:
http://www.loptics.com/ATM/diagonals.html
Gives similar results to Bartels' page.
Its useful to calculate L (distance from the secondary mirror to the focal plane) for your particular scope (this from a Gary Seronik article):
[image] [/image]
My scope yields a number of 10.2" for L. If you know focal ratio (in my case 4.72) you are set. Dividing 10.2/4.72 gives me 2.16" for minimum size of the secondary.
Interestingly, this is backed up by the Newt program online.
[image] [/image]
Here is a handy ray-trace using Newt:
[image] [/image]
This configuration is by the numbers....which may be great for strictly planetary work. I am not interested in limiting the scope to planetary views and want a real-life solution.
Bartel's page and Mike Lockwoods' (respectively) provide perspective on this, and using their calculators and tables, give me a number very close to the stock secondary diagonal size!
[image] [/image]
[image] [/image]
2.48" or 63 mm is the stock secondary size for
Thanks for reading to the bottom,
Ian