Astro-Tech 6″ f/9 Ritchey-Chrtien Astrograph

Description

Focuser drawtube travel is 34mm, while back focus between the focuser’s 2″ accessory holder and the focal plane is 150mm. The December 2009 issue of Sky & Telescope said that “the infinity focus of the AT6RC falls 9-3/4″ outside the back of the telescope, allowing plenty of room for all types of cameras, filter wheels, and ancillary equipment.”

Two extension rings (one 1″ and one 2″) are provided to thread onto the rear of the scope (singly or in combination) between the scope rear cell and the focuser. These form a very rigid and tilt-free extension that moves the focuser out from the rear cell to accommodate the varying back-focus requirements of webcam/Deep Sky Imager-type cameras versus DSLRs. Typically, both rings (one 1″ and one 2″) will properly position most DSLRs at the AT6RC focal plane. Sky & Telescope pointed out that the “1- and 2-inch extensions, as well as conventional extension tubes that fit in the 2-inch focuser, mean that you can always assemble the system so it comes to focus with whatever camera and accessories you’re using.”

While it is possible to use large CCD cameras and filter wheels with the AT6RC, these cameras are generally not recommended. The weight of a standard CCD camera and the color filter wheel typically used with it may cause the focuser drawtube to tilt slightly when fully extended, affecting the focus. Adding an optional Feather Touch focuser (our part #FT-1.5BC), plus an optional 90mm x 1mm pitch adapter (our part #M90X1), will eliminate any such potential problem, although at significant additional cost (more than double the cost of the AT6RC itself).

For even more impressive coma-free DSLR imaging with the AT6RC, consider adding the Astro-Tech AT2FF field flattener. This modestly-priced imaging accessory essentially eliminates the residual field curvature inherent in all reflector telescope designs, so that the coma-free star images remain point-like all across the field of the APS-C size imaging chip used in most DSLR cameras. Use of the #AT2FF with a DSLR will typically requires one optional #AT2EXT 2″ extension ring, instead of the two rings generally needed with a DSLR camera alone.

Compression ring accessory holders: The focuser drawtube ends in a 2″ accessory holder that uses a non-marring soft brass compression ring to hold 2″ imaging accessories in place. The compression ring won’t scratch the barrel of your accessories as an ordinary thumbscrew can. Also supplied is a 1.25″ accessory holder that slips into the 2″ compression ring holder to let you use 1.25″ imaging accessories. Like the 2″ eyepiece holder on the eyepiece holder rotation mechanism, the 1.25″ adapter also uses a non-marring soft brass compression ring.

Mounting dovetail: a Vixen-style dovetail bar runs the length of the underside of the optical tube. The dovetail can be removed, if desired, so the AT6RC can be installed in optional user-supplied mounting rings for piggyback mounting on a larger scope. An optional #AT6SDP Vixen-style dovetail is available for mounting on top of the AT6RC to allow you to mount an optional photoguide scope on top of the astrograph.

Finderscope dovetail: a Vixen-style finderscope bracket dovetail base is installed on the upper left side of the optical tube. It can easily be removed if not needed. It will accept Vixen-style finderscope brackets as well as red dot-type finders, such as the Astro-Tech #ATF.

Other accessories: A snap-in dust cap is standard.

Tech Details:

Supplied Accessories:

1″ and 2″ extension rings for fine-tuning the back focus
Vixen-style dovetail rail