Astro-Physics Apochromatic Refractors
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The optical design of all lenses currently in production is patterned after the 6" EDF astrograph objective. The EDF design uses synthetic fluorite, FPL53, which has excellent optical, mechanical and thermal properties. Although it is the most expensive E.D. optical glass currently available, its singular ability to bring a wide spectrum of colors to a common focus places it several notches above the nearest rival. The two mating crowns that make up the final triplet assembly are chosen to compliment the E.D.'s optical characteristics as closely as possible, resulting in a well-corrected spectrum range spanning 6000 Angstroms. While the color correction was originally chosen for photographic emulsions, these lenses are especially well-corrected for the critical visual colors from red to violet. This makes them superb planetary instruments, easily rivaling and outperforming the old long-focus doublets. The following link shows the color correction curves for the 160mm f7.5 StarFire EDF refractor.Optical Production and Testing Standards
Every production run starts with optical glass purchased to our specifications. Each blank is inspected and tested by our suppliers to meet our homogeneity and quality standards. These blanks are then processed in our computerized facility and hand-figured by experienced opticians. Each surface is polished to a fine sphere and tested by test plate interferometry. Three elements are then matched and assembled as a set. Final figuring on the front and rear surfaces is done using our green light Fitzeau interferometer which checks the wavefront accuracy. The interferometer immediately shows when a polishing lap is worn when zones develop on the glass surfaces. A new lap can then be made without guesswork to again produce a smooth surface.
The finished lens is then coated and assembled in a precision cell which is fully temperature-compensated. The cell is attached to the tube assembly and the optical alignment is checked at high power on an artificial star. The lens is serialized and all test data including final interferogram are stored in a computer file along with the customer's name. Our extensive hand-figuring techniques and the use of high quality blanks allows us to guarantee that all production lenses will meet the 1/50 RMS (98.4% Strehl ratio) minimum limit.
Construction of the Tube Assembly
The mechanical construction of Astro-Physics refractors makes the scopes completely trouble-free and keeps the optics permanently aligned. Their gorgeous tube assemblies are precision machined in our shop with modern CNC equipment. There are no fragile die casts in these telescopes. Our expert machinists transform solid, aircraft-quality aluminum into a fully baffled tube assembly with a large number of knife-edge baffles. This eliminates as much stray light as possible for maximum contrast at the eyepiece. The exterior finish of the tubes and dewcaps will retain their deep, lustrous beauty for many years.
We have incorporated several significant improvements to the tube assembly to make it easier to transport and set up in the field. The dewcap slides over the lens cell for more compact storage. An aluminum dust cover protects the optical surface when not in use, and a foam-fitted carrying case will help retain the beauty of your tube assembly for years. You will appreciate the unique design and fine craftsmanship of these fine telescopes.Astro-Physics 2.7" Focuser (27FOCU2)
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Copyright © 2012 Astro-Physics Inc. All rights reserved.
Last modified: January 4, 2012
11250 Forest Hills Road, Rockford, IL 61115, U.S.A.
Phone: 815-282-1513 Fax: 815-282-9847