Posted 13 May 2014 - 05:05 PM
So, here's what I have to build:
1) secondary mirror holder
2) secondary mirror corrector mount and collimation screws
3) tube or connectors joining corrector mount and main mirror mount.
4) Hyperstar to tube mount
5) Hyperstar to camera adapter
I have a metal lathe (7"x14") and a small milling machine. I'm planning on making most parts on the lathe. I have never done any threading on the lathe, but am willing to learn for this project. Here are my ideas on how to do the above items (your input welcome):
1) secondary mirror holder - I've ordered one of these from Astrosystems. Would have built it myself, but I don't have good skills with sheet metal.
2) secondary mirror corrector mount and collimation screws - I was hoping to use the existing collimation mount in the C8, but it's an older glued in version, and the secondary mirror holder cannot be removed without removing the glued in secondary light baffle. Ideally I'd like a Starizona Hyperstar adapter, but I paid as much for my lathe as one of those costs, so I'm going to build one. Again, ideally, I would like to build a Hyperstar compatible secondary mount so I could swap my diagonal flat for the cassegrain secondary and use the scope both ways. I may or may not make a unit which is full Hyperstar compatible. I only need an adapter which will mount the Newtonian secondary,and may build that first before opting for the more complicated Hyperstar setup. I would really like the Hyperstar setup since this would give me the option of using the scope as a SN, SC, or Hyperstar Schmidt.
3) tube or connectors joining corrector mount and main mirror mount - I would prefer to not modify the old C8 orange tube primarily for resale reasons. That leaves me with choices about what to do instead. Since the prototype phase of the project will be so experimental, I think I'd like to not use a tube and use some sort of tube end connections instead so I have working room to fiddle around in the optical path to try things out. I'm thinking about using 3 inch aluminum channel top and bottom with maybe side truss(es) to experiment with. The Hyperstar mount could easily be mounted to the channel on top. A nice flat mounting suface gives me more options.
4) Hyperstar to tube mount - This could be as simple as a ring mounted to the top channel with a locking screw or as complex as a genuine Hyperstar-like screw mounting. Again, I don't have screw-cutting experience, so this seems daunting at this point.
5) Hyperstar to camera adapter - This is the only part which will absolutely require threads being cut. I've got a Canon T-mount which has the t-threads in a ring which is held into the bayonet mount with set screws. I would be making one with the same OD as the current t-thread unit but with the Hyperstar threads instead. I would also be machining the adapter to put the Hyperstar focal plane coincident with the camera focal plane. I could conceivably buy the Hyperstar C8-T-thread adapter, but the unit backfocus does not work with Canon DSLRs. However, I did measure the unit, and it is possible to build a lower profile Canon adapter which would allow use of the Hyperstar. This was the whole purpose for building the SN-C8 so I could use my DSLR with it.
Would appreciate any brilliant ideas that I've overlooked,