Posts tagged 'Ritchey-Chrétien'

They Do It With (hyperbolic) Mirrors

Posted by on October 11th 2010 in Astrostuff, Shiny new kit, Thanks

I wouldn't have bought this if it hadn't been on offer and if I hadn't managed to get a further significant discount.
It takes up less room on the mount than the big black 8-incher does and it doesn't catch the breeze so much, so it's a lot more stable.
Add to that the facts that it's lighter, more portable and gives a much bigger flat-field for imaging, and it was a no-brainer.



For those with an interest in such things, it's a GSO GSRC6M 6" f/9 Ritchey-Chrétien Astrograph as supplied by Teleskop Service (as opposed to the Astro-Tech version marketed by Astronomics). The Ritchey-Chrétien design is favoured by many professional observatories (including the Hubble Space Telescope) and by some high-end amateurs for many reasons (the absence of any refractive elements, the fixed primary mirror, the coma-free image capability etc.) but until recently they had been expensive beasts compared to other Cassegrain designs. I've wanted one for many years and when the chance to get one came along I grabbed it with both hands.

FWIW, here are some of the specs:

  • Design: True RC (Ritchey-Chrétien) with a hyperbolic primary and a hyperbolic secondary mirror. No glass corrector plates or lenses in the optical train
  • Aperture: 6" (152mm), Focal Length 1370mm, Focal Ratio f/9
  • Primary Mirror: BK7- surface quality 1/12 Lambda or better, 99% dielectric high-reflectivity coating
  • Secondary Mirror: BK7, 99% dielectric high-reflectivity coating. Robust collimatable cell. Complete obstruction = 77mm
  • Construction: Steel tube with alloy primary and secondary mirror cells. Total weight 5.4kg
  • Focuser: Axially-rotatable 1:10 dual-speed Crayford focuser for extremely smooth focusing with no image-shift, accepts 2" and 1.25" accessories

Just in case you were wondering, it is currently on offer discounted from 898 Eur to 499 Eur including tax... suffice to say that a polite request to TS resulted in a favourable deal at a much-reduced total cost and including a GSRCV50 50mm spacer placed between the focuser and the telescope. At this point I must thank Wolfi Ransburg of TS for the great deal - thanks, Wolfi!

Typically, we've had cloudy nights here ever since the thing arrived 🙁

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