I am no better than you. I am still learning. this is a complete new area for me. Worse than U, I am gambling.鄧登凳 寫: I have no experience in making or designing Newtonian astrograph. I just want to learn more from you on the design.
The lowest profile focuser I found has a minimum height of 55 mm, this is a design constraint. Except than I make my own focuser ( which is not quite possible considering my poor craftmenship ) 165 mm is the minimum I can go for.鄧登凳 寫:
Your focal plain has a radial distance of 110+55=165 from the principal axis. The mirror has a radius of 102/2 = 55. So is there a reason why the MPCC is not moved much closer to the principal axis? Moving the MPCC closer to the principal axis also allows the use of a small secondary mirror and reduce central obstruction.
A Newtonian you mention is not suitabe :-鄧登凳 寫:
There are many cheap 4 to 5 inch Newtonians around, why don't you use their cell/body and just focus your effort on the optical part?
1. they have a focuser not up to astrograph requirement - not low enough profile, not zero backlash and incapable of housing a 2 inch MPCC.
2. their tube is not strong enough to hold the tight alignment precisely under long exposure. Don't forget my Epsilon has a speed of f/3.5
3. Their tube is too long, too fat to be carried around.
4. Circular shape OTA is very difficult t9o be packed inside a suitcase.
5. I like things to be flat packed. So the OTA will be rectangular in shape, ready to be dismantled and flat packed inside my suitcase- mimimum space for maximum capacity. Rectangular OTA still not seen on the market.
Thanks for your questions and suggestions. As I always maintain, your voice is always my best teacher. Looking forward to hearing again from you soon.
Best regards
Chan Yuk Lun