Well, I realized I still had more fingers on one hand than astronomy projects in progress, so I started another!
Actually, I very nearly started a project like this nine months ago and came very close to pulling the trigger on buying a Discovery 8" f/8 mirror then. They had them in stock at the time. I started an exploratory thread then that ran a few pages and can be found here. I want to have at least one unobstructed reflector in my stable, and love how Ed Jones has worked out a way with two lenses to make reasonably fast optics perform adequately while completely unobstructed.
When I added up the cost of primary, secondary, two lenses from Newport, and a few accessories last year, I decided instead to start building a 12.5" f/4.3 dob that I actually already HAD a mirror for. That project was 90% complete before this year's June Cherry Springs Star party and is still waiting to be completely done. I've had a beastly hot summer and haven't been inclined to play in my uninsulated garage after spending at least six days a week in a large plastics factory where indoor temperatures are always at least 10 degrees F hotter than outside. That project will resume shortly in parallel with this new build. Temperatures are getting bearable again after the hottest July on record both locally and worldwide.
I decided last year to keep my ear to the ground and continue to watch CN classifieds in the "ATM Parts and Stuff" for reasonably cheap reasonably appropriate components for this project. Well, about a week ago both an 8" f/10.6 primary that had been tested quite favorably by Mike Spooner and some 2.75" secondaries both were advertised at VERY reasonable prices. What a community!
I now have the mirror, and the secondary is on the way. Newport reportedly shipped yesterday the two lenses Ed Jones has specified. This mirror strikes me as almost ideal for this project, except at 1 3/8" thickness it is the thickest I've built with. A cooling fan will definitely be in the design. Being f/10.6 it should do well with the same radii concave and convex lenses I've ordered, according to Mr. Jones.
I've been pestering Ed Jones with questions via PM the past week and he has provided me with rough dimensions to consider in the design. Despite an approximately seven foot focal length, it appears that with a 2.75" secondary (used sideways) I can fold the light path low enough before the lenses to place the eypiece only about four feet from the primary. YEAH! This will have the aperture and approximate focal ratio of a C8 with the eyepiece not much higher than that of an 8" f/6 dob!
Anyway, I'm starting this build thread, if for no other reason to motivate me to keep this project moving along at a reasonable pace for a sense of pride. I've enjoyed looking through Kevin Frederick's 17" chief at Cherry Springs and want to see how well a reasonably priced smaller version will perform. I have the benefit of both a well appointed woodworking shop at home, and access to water jet robots and CMM equipment at work (both of which I have experience using). I may make a "top box" that precisely holds the secondary, lens cell, and focuser in their relative positions as Kevin did, and then build the rest like a more traditional dob. My mechanical design hasn't been envisioned yet. Ed has warned that if a fixed design doesn't work, "then where are you?". I don't mind taking that risk because I could have a do-over without significant expense because I expect to be my own fabricator.
Wish me luck, and come along for the ride!
Edited by jtsenghas, 27 August 2019 - 11:10 AM.