Altair 6" F12 M-LRS Classical Cassegrain Telescope OTA

The Classical Cassegrain design is ideal for for high resolution lunar and planetary observing and imaging. This 6" version has to be one of the best value instruments of it's type on the market today and is easily carried on an EQ3-2 or EQ5 mount, with a 500mm tube length of less than most 6" Newtonians. It also has better on-axis sharpness than a Schmidt Cassegrain due to the lack of a corrector plate, and doesn't dew up as easily.

This example can be thought of as a long F12 focal ratio Newtonian, but in a much more compact optical tube, allowing the use of popular equatorial mounts, which would be impractical with an 6" F12 Newtonian. What's more, the optical tube is open, allowing faster cool-down than a Schmidt Cassegrain or Maksutov Cassegrain. 

The advantage of the rear focus point not only gives you a convenient eyepiece position for longer more relaxed observation, it also let's you use the Altair "Big Prism" Bino-viewers for incredible views of the Moon and planets. We recommend the Altair UltraFlat eyepieces which give razor sharp views with this telescope.

For high resolution lunar and planetary imaging, the placement of the focuser makes fine adjustments so much easier when seated behind your laptop, a refreshing change from the contortions forced on us by other telescope designs! The capture of fine details with your GPCAM or Hypercam camera becomes easier than ever.

Of course you also get 6" of aperture with zero colour aberration just like an APO due to the use of an all-mirror design. One application where the Classical Cassegrain outperforms Schmidt Cassegrain and some refractor designs, is the control of optical aberrations in the further reaches of the red and blue spectrum. This allows very productive use of the Altair Planet Killer filter, and the Altair 7nm NUV filter for Venus (and the sun, with an appropriately sized Baader film on the front of the telescope). In fact, high resolution imaging of the sun in white light is also very possible with Baader film, and the relatively large aperture will easily allow views of solar granulation. Note: We do not recommend the use of a Hershel Wedge with this telescope, however, because the inside of the tube or baffle can easily overheat if solar rays strike it.

The primary mirror is fixed to the tube, eliminating image shift when focusing. This makes focusing easier than with some older Schmidt Cassegrain telescope designs. The 2 Crayford focuser has a 10:1 Dual Speed fine focus knob for precision small movements. These features make focusing easy, and much smoother at high power.

Three CNC-machined spacer rings are included allowing a large range of accessories to be used such as the Altair Atmospheric Dispersion Corrector (ADC). They can be removed for use with Altair Binoviewers or Flat Field Barlows. A 2" to 1.25" adaptor and standard finder scope bracket are included, so you can use the Altair 50mm or 60mm finder scopes.

Interior knife edge baffles reduce stray light for maximum contrast, even on the moon, and the mirrors are accurately made from BK7 by leading Taiwanese manufacturer GSO, employing CNC polishing techniques. Our views through this telescope have shown the mirrors are in the "good to excellent" category, at a price point which is quite remarkable.

Fitted with a Vixen-style 44mm dovetail mounting plate on the base to fit most mounts on the market.

Altair GSO 6" F12 M-LRS Classical Cassegrain Telescope OTA features:

• 154mm (6") aperture
• 1848mm focal length
• f/12 focal ratio
• Fixed primary
• Parabolic BK7 primary mirror: ~96% reflective aluminium with SiO2 protective coating
• Hyperbolic BK7 secondary mirror ~96% reflective aluminium with SiO2 protective coating
• Secondary mirror obstruction: 38% (comparable with SCT telescopes)
• Multiple baffles inside the optical tube affording good contrast
• 2 Crayford focuser with 10:1 Dual Speed microfocusing
• Vixen/Synta Style Finder scope base
• Vixen-Style 44mm Dovetail 
• Extensions supplied with 2x 25mm and 1x 50mm CNC-machined focuser extension rings with matte black baffled interiors.
• Weight 5.4kg, Length 500mm Approx.