Telescope-Service: Ritchey-Chretien (RC) Telescopes

Real Ritchey-Chretien (RC) telescopes share many design principles with the classical Cassegrain concept. They are known for their excellent photographical performance.

Two mirrors without a correcting lens produce a large field free of coma. The image field has a strong curvature, though, resulting in a very small usable field. For this reason the RC telescope is equipped with a correcting lens close to the focal plane. This lens corrects for the field curvature, resulting in a very large usable field at a very high resolution.

In direct comparison with a classical Cassegrain the RC telescope offers a corrected field that is about three times as large. For this an RC must be very carefully made, otherwise the very good theoretical performance would not be passed on to the real telescope.

Main Fields of Use For RC Telescopes

RC telescopes offer a very large, well corrected field. For this reason RCs are ideally suited for astro-imaging. Very many of the best astro-images that you can find throughout the internet are made with Ritchey-Chretiens. The RC is particularly effective with the new generation of digital and CCD cameras with their very high image resolution.

On this page Telescope-Service offers only true RC telescopes, not variants or entirely different telescope designs. It is this exact telescope design that has been in frequent and successful use among professional astronomers for many years. And now this telescope is also available for amateurs.

Optics:

- Type: Ritchey-Chretien (original optical layout, not a variant)

- Aperture: 250mm

- Primary mirror focal ratio: f/3

- Secondary mirror diameter: 96mm

- Effective focal ratio: f/8

- Effective focal length: 2000mm

- Primary mirror substrate: LK-5

- Mirror coating: Aluminium coating with Quartz protective coating

- Maximum usable film (chip) sizes and equivalent field of view: 4.5x6cm or 6x6cm format (1°15'x1°40' or 1°40'x1°40')
- Maximum Back Fokus 117mm

Mechanics:

- Tube weight: 15kgs

- Weight including tube rings and finderscope: 17.8kgs
- Base plate - 160x105mm with central M8 thread (further mounting adaptations are possible)
- Eyepiece / accessory attachments: M84 x 1 thread, M77 x 0.75 thread, M60 x 0.75 thread, 2", 1.25"

Further Details:

The Astrosib 250 RC has a number of properly positioned baffles for optimized contrast and suppression of stray light.

The secondary mirror of the Astrosib 250 is held in a massive cell with covered collimation screws.

With these knobs you can release the tension of the tube rings. You can then rotate and move the tube in the rings.

Off Axis Guider - Included!

A further advantage of the large corrected field of the RC is that you can use an Off Axis Guider with ease.

Despite the fact that the focuser has a clear aperture of 80mm the star image within the Off Axis Guider's 1.25" barrel is well defined. As a result finding a suitable guide star is possible without a problem.

The Off Axis Guider is attached to the focuser with an M105 x 0.75 thread. By loosening the locking screw you can then rotate the Off Axis Guider by 360°.

For camera connection a mechanical 2" reducer is included. Even if you use the full 2" field the prism of the Off Axis Guider doesn't block any light.

Into the Off Axis Guider you can insert 1.25" eyepieces. The Off Axis Guider has an integrated helical focuser for the eyepiece.

Please send requests or online orders to: sales@telescope-service.com

TOSCANO - Ritchey-Chretien (RC) Telescopes

Secondary mirror spider for Toscano 10" f/9 RC telescope

8" F9 Toscano RC

Specifications:

- Primary and secondary mirror substrate: Pyrex
- Secondary mirror diameter: 71mm
- Linear obstruction: 35.5%
- Diffraction limited field of view: 16mm diameter
- 90% field illumination: 54mm diameter
- 100% field illumination: 19mm diameter
- Back focus: 200mm
- Tube weight: 8kgs
- Focuser: Crayford focuser with 1:10 dual speed microfocuser
- Optical quality:
Standard optics: 1/20 wave RMS surface quality per optical surface
Deluxe optics: 1/40 wave RMS surface quality per optical surface

Prices:

Standard optics = 2775.- Euros (incl. VAT)
Deluxe optics = 3465.- Euros (incl. VAT)

10" F9 Toscano RC

Specifications:

- Primary and secondary mirror substrate: Pyrex
- Secondary mirror diameter: 87mm
- Linear obstruction: 35%
- Diffraction limited field of view: 20mm diameter
- 90% field illumination: 54mm diameter
- 100% field illumination: 19mm diameter
- Back focus: 250mm
- Tube weight: 13kgs
- Focuser: Crayford focuser with 1:10 dual speed microfocuser
- Optical quality:
Standard optics: 1/20 wave RMS surface quality per optical surface
Deluxe optics: 1/40 wave RMS surface quality per optical surface

Prices (with standard focuser):

Standard optics = 4710.- Euros (incl. VAT)
Deluxe optics = 5585.- Euros (incl. VAT)