[Doomsayer]

Hi Jason
Good to see you're nearly at the end. These are not easy things to build!
As you know I built two similar RC truss scopes using the same optics (shown on a thread here some time ago).

My designs are quite different and use a very beefy Van Slyke secondary mirror focuser & spider. I started my RCs at about the time you got your mirrors as I recall (I have been in touch with Jason quite a bit during the throes of construction off forum and on CN). Both scopes are performing well now - I had a few teething problems with alignment of some components which took me a while to sort out. It is a very 'solid' scope - which really needs a PME or an AP1200 to carry it with extra gear.

Paul Jones (optician at Star Instruments USA) told me that mirror separation should be within a few mm (not super critical) but that concentricity and relative 'squareness' of the two mirrors is more critical (plus any subsequent collimation). So placing the image plane at the right position for optimum mirror spacing is a bit tricky in these short backfocus RCs.

Because these f6.7 RC optics have a relatively short backfocus of around 9 inches from the front surface of the primary, I felt that a secondary focuser is essential - especially if the rear plate of the OTA and the primary mirror cell eats up a few inches of backfocus - and also if you want to have a large camera rotator and an off axis guider in front of the camera.

The two RCs have a doublet field flattener which reduces the backfocus to 8.5 inches. I plan to upgrade my Pyxis 2" camera rotator to the 3" one before long. Still saving pennies for a bigger camera - likely an FLI 16803. I have the loan of an STL6303 as of yesterday for a short while - hopefully I'll get the chance to use it with weather and other to-do's that get in the way.

cheers
guy