Double Truss Configuration
The double truss configuration allows a heavy secondary cage without having to use counterweights, by allowing the altitude trunions to be mounted near the midpoint of the Optical Tube Assembly. The following photo shows the double truss assembly with the rotating secondary cage removed.
(Click on the image to see a large image of the double truss and more details)
The secondary cage is relatively heavy due to the rotation bearings (the sec cage rotates to allow more comfortable viewing), and the image plane derotation system, as well as a heavy finder, a camera/eyepiece slide, and a camera.
(Click on the image to see a larger image of the Rotating Secondary Cage with much more information)
The primary mirror cell has a Plexiglas cover that is hinged open. When it is open, it does double duty as an extra dew shield for the primary mirror.. The rear of the primary mirror box has a DC powered fan to aid cooling of the 2"thick primary mirror. All collimation adjustments are accessed from the front. The collimation system is a 3 point design, using 3 corners of the square plate that forms the rear of the cell. The mirror rides on a 9 point flotation system.
The light sock is in three pieces. The main sock is a tube with internal plastic rings to help hold its shape. It is stretched between the sec cage and the primary mirror box. The sock slips over the rear of the sec cage to seal out light at the forward end. At the primary mirror box, there is a second sock that slips over the primary mirror box and over the truss assembly to seal the light at the bottom end. The aft sock can be seen temporarily stowed around the primary mirror box in the picture above. The forward light sock (light shield) is a 1/4" foam sleeping pad rolled into a cylinder and joined with Velcro, and attached with Velcro to the front of the secondary cage. (it is the green cylinder on the front of the scope). The light sock system is effective enough to allow ccd imaging with a street light at the end of my driveway...
