Here are the basic plans for the promscope(coronagraph) that David designed. Twenty of these units were built in a weekend when David's club, the Delmarva Star Gazers (www.delmarvastargrazers.org) hosted a telescope making weekend in Spring. The telescope provides excellent views of prominences. Most of the parts can be obtained at the local home Improvement store. The optics and metal telescope tube came from Apogee. The 10 Angstrom 656 H-alpha filter came from Maier Photonics that was used for the class. The original prototype used a filter from Andover Corp. The telescope can be built for under $300 and only requires hand tools.
The "cones" picture shows the brass 1/4" diameter ferrules that David uses for the occulting disks. They came out of 1/4" Swagelok plumbing tee used with 1/4" copper tubing. The ferrules at attached to 1" long 1/4" diameter "stand-off" The stand-off has a thread hole down it's center and the ferrule is held on to it with a 8-32 bolt and washer. The stand-off is commonly used to mount circuit boards. It is epoxied to the center of the field lens The image also show a 24" mm OD adjustable iris that is placed between the relay and field lens and used to adjust the contrast of the image.
All the optics, iris and filter are mounted inside 1" standard copper tubing. The parts are held in place with 4-40 set screws. The lens and filter have masking tape applied to the edges for a better fit and also so the set screws or not pushing against bare glass. The inside of the copper tube is lined with black flocked paper to reduce stray light.
The copper tube is placed inside a chromed 12" x 1- 1/4" sink trap extension. The flaired end of the sink trap is 1- 1/4" ID so it fits standard eyepieces. The outside ends of the copper tube are wrapped in a few turns of 1/2" wide masking tape to makes up the difference in diameter between the outside diameter of the copper tube and inside diameter of the sink trap. The sink trap with the optics becomes the focusing tubing for the telescope and fits nicely into a 1- 1/2" PVC to 1- 1./4" The end of tube is stabilised by three nylon tipped set screws, placed about 1-1/2" behind the PVC sink trap adapter and at 120 degree centers. The sink trap slides easily into and out of the adapter so one can focus the image, then can be locked by tightening the plastic nut on the sink trap adapter.
These are pictures of David's latest project, his solar spectroscope. It was made from two 65x900mm lens, a 3 3/8 inch diameter flat and a 600 lines/mm grating blazed at 500 nm. The grating is rotated by a small DC motor located under the main housing. By using inexpensive PVC plumbling parts and plywood, the cost was kept down to under $50. The amount of detail visible in the solar spectrum is amazing. (David.M.Groski@usa.dupont.com)