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Astromart.com: Stellarvue Nighthawk BV Review

Stellarvue Nighthawk BV.jpg

Jim Carpenter reviews the Stellarvue Nighthawk BV over at Astromart.com and recommends the "well-corrected, moderately-priced, achromatic refractor" telesscope to potential buyers. 'This topic for this review is the Stellarvue Nighthawk BV, which is based on the telescope formerly known as the Stellarvue SV80/9D, a well-corrected 80mm f-9.4 doublet achromat. The SV80/9D was always a sleeper in the Stellarvue lineup. Despite its noticeably better performance, it never attained the popularity of its f-6 sibling, probably due to the fact that it was not “airline portable.” The Nighthawk BV is nothing more than a Stellarvue SV80/9D with the optical tube assembly (OTA) shortened by approximately 4 inches, which is the length the light passing through the binoviewer adds to the optical path. Before going further, let’s make one thing clear – despite the use of “Nighthawk” in this telescope’s name, it is a totally different animal than the 80mm/f-6 Nighthawk Classic and the newer Nighthawk II.

The Nighthawk BV not only has a longer focal length (750mm), it also uses a glass type with a higher Abbe number than the f-6 Nighthawk in one of the elements. For those new to this hobby, the short definition of the Abbe number is a value used to define color dispersion — the higher the number, the better the color dispersion. It is named after the German optician who developed the mathematical formula for determining this value, Ernst Abbe (1840-1905), who was a professor at the University of Jena and was a co-founder of Ziess Optics. The typical crown/flint glass used in achromatic refractors have an Abbe number in the low 60's. At somewhere between 70 and 80, depending upon which authority is speaking, the glass becomes “extra-low dispersion” (ED) type, and at 90 and above it is considered “super-low dispersion” (SD). Glass types in the SD range are what are typically found in premium apochromatic refractors. While Vic Maris, the owner of Stellarvue, declines to call the SV80D an “ED” refractor, he has nevertheless stated that the Abbe number for the glass used in the lens is “above 70.”

Read: Stellarvue Nighthawk BV Review - Astromart

Posted by Slash Scope Admin on July 15, 2006 04:46 PM |

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