Small steps. Let's not turn my teasing comment into a full scale hijacking. I did investigate 3" lenses in the past and things get expensive fast.
This group build is a great idea in my mind at its scale, and 8" f/7 is small enough for most for it to be portable and relatively uncomplicated. Considering that these lenses cost about the difference between a good 10" primary and an 8" primary, these 8" Chiefs should cost little more than 10" dobs to build.
Those of you who are in for this group build should be thinking about the other purchased components. I've decided my longer 8" Chief will only use 1.25" eyepieces, which also made an optional dielectric tertiary cheaper and lighter.
I imagine most of you would be satisfied with a 1.25" focuser. If you make your upper end a box structure you'll probably want a newt focuser that attaches easily to a flat surface. If you build as Ed did his last couple you may want to affix a refractor focuser to a tube. Some refractor focusers are nice and long, which allows for flexibility for binoviewers or cameras. Just be careful you don't create a crash condition between your draw tube and mirror cell.
A tube in a tube clamp allows for a little more adjustment in the build, too, both for length and rotation. Ed discovered last year, however, that the tube clamp sizes in the practical diameters for these builds are scarce. Salvaging such hardware from larger refractors or building your own may be required.
I haven't worked out all the details on my upcoming Chief build, but it will probably be a bit more intensive on the woodworking side than most would want to delve into, and I'm still most likely to have hexapod adjustment on my setup for collimation control of both ends.
I urge you to watch Ed's YouTube videos and his "Optical Ed's" (opticaleds.com) writeups on the evolution of these scopes.
I believe the corner frame mount he currently favors was in fact first used on Kevin Frederick's 17" Chief.
I'm anxious to see what mechanical designs some of you come up with. A fork design sounds excellent to me.
These 8" diameter primaries are small enough that only particularly thin mirrors wouldn't be adequately supported with a three point mirror cell with no moving parts and the back supports anywhere near 40% of the mirror radius.
Don't forget, though, to build your cell at the tilt angle of the optical design, which is 3.4 degrees here. This could be as simple as angling a dob tailgate at that angle.
Edited by jtsenghas, 18 August 2020 - 02:13 PM.