Built a RC300

A Ritchey Chrétien is born..

Updated on January 22, 2009

	The following pictures show the step by step building of a 12" f/8 R-C carbon fiber ota. After years of use I decided to upgrade from Schmidt-Cassegrain telescope to Ritchey-Chrétien even if I never built a telescope, this configuration have a low field curvature and is more fast, it also have not a corrective plate, only two hiperbolic mirrors. The picture on left show my lathe work on the external tube ring. I made a wood sample then a foundry melted in alluminium, so I obtained two raw rings. I had to built a support to lock the ring on the lathe.
	Unfortunately I didn't took images of the carbon fiber tube building; I made a wood tube sample, then 5 meters of carbon fiber fabric were rolled up on it, I used 1 kg of epoxy resin to glue it, then I baked the tube for 2 hr at 50°C. The size are: 35 cm diameter, 80 cm long, 2 mm tickness and a weight of 1,3 kg, a very light and stiff solution! It was the most difficult part to built of the project. The picture show the raw carbon fiber tube with two rings on.
	This image show the lathe work on the back plate, starting from a 12 mm alluminium sheet at first I cut a circle then I work to make two parallel surfaces. The final tickness became 10,5 mm, I hope it's enough stiff to load the primary mirror..
	The back plate on the back ring nearly finished, I used 10 steel screws to lock together, in the center there is a focuser adapter, it fit the TCFS motorized focuser.
	Something that seem a telescope.. The carbon fiber tube was locked in the rings with 10 screws from the inside (each ring), carbon tube was finished with a transparent car paint, under the tube there is a Losmandy plate and at the opposite a 10 mm plate.
	Drilling the fan holes on the back plate, this was a problem becouse I have not a milling machine, by the way the holes are well done and sharp enough.
	The back plate with 3 fan grids.
	These are the primary mirror cell plate and mirror locking tube, starting from a 10 cm solid alluminium tube I bored out inside until a 7,6 cm, then I thread the parts.
	The 9 points floating mirror cell nearly finished, I drilled the main plate to lighten a bit, the 3 triangular plates will load the mirror and are locked to the main plate with 3 steel balls, they can fluctuate but can't rotate.
	The back plate was painted black, then I installed the 3 fans and soldered the lines to a external connector.
	Ready for the mirror.. The back plate and mirror cell are finished, all was painted black to avoid any kind of light reflections.
	I like it!!!
	But I have to build something more.. This is the secondary mirror spider support, the 4 blades are missing, at the top there is a secure bolt avoiding mirror to fall on the primary, with this support I can change the backfocus.
	The secondary spyder support ended, all was painted black matt, the weight is around 1.5 kg with the mirror placed.
	Primary and secondary Pyrex mirrors. Made in Italy by Mr Germano Marcon of Ariete Telescopes and Optics, a great craftsman, he made the mirrors with his hands and with great accuracy.
	All is in his place. The internal surfaces will be covered with a flat black adhesive paper to avoid any kind of light reflections. I will add an alluminium ring near the secondary spider avoiding flexture of the carbon fiber tube.
	Recently was added a selfbulted RC control box. It control the heater dew shield temperature on the secondary mirror, the water flux of the ccd cooling system and the fans of the primary mirror.
	A new design primary and secondary mirror (on left) light shields were added to the RC to remove some lights infiltration.
	Cad multiple viewpoints
	Telescope specifications: Type Ritchey-Chrétien f/8 Focal length 2432 mm Primary mirror diam. 304 mm Secondary mirror diam. 119 mm Primary mirror hole 81 mm Mirrors spacing 607 mm Averall length 800 mm Field in the focus plane 50 mm Total weight w/o ccd 20,8 kg Mirrors are made in Pyrex ___ At the end of this project I can say that it was not simple at all, but i feel a great satisfaction! I have to thanks my friends Alessio and David for the help and Mr Germano, the mirrors man!
	Screenshot of CCDInspector that show the collimation of the RC at f/8, ST10 ccd camera and AO7 (without a field corrector).
	Screenshot of CCDInspector that show the curvature map of the RC at f/8, ST10 ccd camera and AO7 (without a field corrector).
	This is the first light!!! After a fast collimation i try on a easy object, Messier 27, 15 minutes with H-Alpha filter, ST10-CFW10-AO7, bin 1x1.
	Another test on NGC 5907, a 40 minutes luminance, ST10-CFW10-AO7 bin 1x1.
	The RC work really fine until I upgrade to a large format ccd like the STL11000M, with a 42mm ccd diagonal the telescope need a field flattener. I placed a single element corrector inside the primary mirror locking tube, 208 mm from the focus plane. Corrector made by Columbia Optics.
	The new primary and secondary mirror carbon fiber light shields, redesigned to have a 50 mm clear field in the focus plane. I saved about 400gr compared with old alluminium light shields (need painting).
	This is the alluminium ring that I placed over the primary mirror, it is 3mm narrow than the mirror. It should improve the stars aspect.
	This is the new adapter set that I built for a proper flattener-ccd spacing: 1- RC rear cell adapter 2- Rear cell to PDF focuser 3- FLI PDF 3" focuser 4- PDF to AOL adapter 5- AOL front plate 6- PDF to Collimator and eyepiece adapter
	Imaging train setup: 1- RC rear cell adapter 2- Rear cell to PDF focuser 3- FLI PDF 3" focuser 4- PDF to AOL adapter 5- Sbig AOL 6- Sbig STL11000M
	A setup test image on Messier 44, RGB composite, 60 minutes total exposure. ___ Andrea Tamanti