| The Takahashi 8.35" aperture CN-212 gives you two very different telescopes in one 34" long x 9.6" metal optical tube. You get a 2630mm focal length f/12.4 classical Cassegrain for high resolution/high magnification observing and an 820mm f/3.9 Newtonian for wide field low power use. The optical principle of the CN-212 is simple yet clever. Its primary mirror is a fast focal ratio 820mm focal length parabolic, with a Cassegrain focus opening in its center. Two different optical configurations are possible, depending on which of two secondary mirrors is placed in its light cone. By using the supplied 68mm diameter hyperbolic secondary mirror to amplify the image and direct the light back through the Cassegrain focus, the CN-212 becomes an f/12.4 classical Cassegrain for high resolution visual observing and high power photographic imaging with a 36mm image circle and a 0.9º field. Replacing the hyperbolic secondary mirror with the supplied 72mm m.a. elliptical flat diagonal directs the light out to a Newtonian focus at the side of the tube instead of to the Cassegrain focus at the bottom of the tube. Attach the supplied low profile 2" eyepiece adaptor and coma corrector/field flattener lens to the Newtonian focus, and you transform the CN-212 into a bright wide field f/3.9 Newtonian. In this configuration a 26mm TeleVue Nagler yields a magnification of 31.5x, a 6.7mm exit pupil, and a huge 2.6º field of view that’s wide enough to encompass all of M31. Photographically, the Newtonian configuration produces a 2.9º field across a 43mm image circle for totally unvignetted 35mm photography. Changing between configurations is a simple matter. Each secondary mirror comes in its own unique housing with a tapered shaft that fits into a conical hole in the four-vane secondary mirror spider. This assures repeatable centering and tilt of the secondary housings. The housings also have an indexing pin that fits into a keyway in the spider to maintain the rotational orientation of the secondary switching between configurations. A knurled thread-on ring locks the secondary housing firmly into alignment in the spider. This combination of cone, pin, and lock ring indexing assures consistent collimation when switching between secondaries. For initial collimation and further routine fine-tuning of the collimation, particularly important for critical high-power Cassegrain imaging, centering marks are provided on the mirrors and a precision collimating scope is supplied as standard equipment. Focusing is by means of a knob on the die-cast rear cell which moves the primary mirror fore and aft in the tube in both Cassegrain and Newtonian configurations. One complete turn of the focus knob moves the primary mirror a mere 1mm, allowing very precise focusing. Back focus is a long 210mm (8.25") in both modes, allowing the use of binocular viewers and CCD imagers. The CN-212 comes with a 7 x 50mm crosshair finderscope that has a wide 6.3º field of view. When set up as a Cassegrain, the tube weighs 18.5 lbs. When set up as a Newtonian, the tube weighs 19.8 lbs. For intermediate imaging requirements, and optional focal reducer (#TNC2100) is available for the Cassegrain configuration. Adding this accessory reduces the focal ratio from f/12.4 to f/9.9 (20%) and reduces the image circle to 29mm, but with a 1.1º field instead of the standard 0.9º field when used at f/12.4.
|
Printer friendly version
Email page link to a friend
Do you have a question about this product?
Terestrial Photography
Lunar Photography
