[el_draco (Rom)]

I scored a set of optics for a 22" F4.5 Newtonian recently and have just about finished the design work. Been a while since I've tried something of this size so I thought I'd chuck up a couple of CAD drawings for comment / Feedback.

The OTA truss framework will be expansion foam filled, welded 50 X 50, 100 X50 and 200 X 50 Aluminium box section with 3mm wall thickness. Primary will be in an 18 point flotation cell with 12 point wiffletree edge support.

Current 100mm secondary will provide about 150mm (approx.) of back focus. I'd like more, but such is life. Imaging focuser will be a PDF with OAG for guiding. No decisions on imaging gear yet. Third image is an interesting graphic showing the off-set of a secondary.

I'm toying with a bearing mounted rotating secondary that can select ports for imaging, visual and possibly a spectroscope. This will necessitate a different adjustment system compared to a standard newt with the secondary becoming the centre of the optical axis. I suspect that's gonna make for some fun and games getting the axis of symmetry right but I have a friendly engineer keen to do the work on this.

Estimated weight is about 75kg all up, without instrumentation.

Clincher is that it will be mounted on my PME 2 via a wide dovetail plate. Obviously observatory mounted.

If I can pull it off, it could make for an interesting system. Any thoughts, especially polite ones, most welcome.