The Astro-Tech AF Series premium 1.25”/2” dual barrel 70° field eyepieces are excellent values, typical of Astro-Tech’s “more performance for less money” philosophy. Each uses a proprietary eight lens/five group optical design to provide a very flat and very wide 70° field of view. They have excellent sharpness and superb field edge performance to go with that very wide field of view, as well as very low geometric distortion and an accurate color rendition.
From the 3.5mm up through the 17mm, the Astro-Tech AF Series eyepieces all have dual 1.25” and 2” barrels. Unlike other dual barrel eyepieces, that use non-removable concentric barrels, the AF Series 2” barrel is simply threaded onto the eyepiece when you want to use a 2” focuser or star diagonal. Unthread and remove it to expose the permanent 1.25” barrel for use with a 1.25” focuser. All 1.25” barrels are threaded for standard eyepiece filters. The 2” barrel only 22mm is threaded for standard 2” filters. The removable 2” barrels of the shorter focal length eyepieces are also threaded for 2” filters, but the inner surface of some 2” filters may contact the concentric 1.25” barrel of these eyepieces before the filter is threaded on fully, scratching the filter. Care should be taken when using 2” filters with the dual barrel focal lengths.
The edges of all Astro-Tech AF Series lens elements are blackened and the interiors of the barrels are finished in matte black with antireflection threading. The resulting low internal reflections give you high visual contrast, with a dark sky background that makes low surface brightness objects stand out more clearly. All lenses are fully multicoated with the latest broadband high transmission/antireflection coatings for excellent light transmission and low ghosting.
Each Astro-Tech AF eyepiece has a long 17mm eye relief, with a roll-down rubber eyecup for essentially non-vignetted eyeglass use. Protective dust covers are provided for both ends of each eyepiece. A plastic bolt-type storage case is standard equipment, not an extra-cost option. 1.5” wide ribbed rubber grip rings on the barrels provide a sure grip when wearing gloves or mittens in cold weather.
Unlike similarly-priced eyepieces whose focal lengths are only silk-screened onto the barrel, and are prone to rub off during use, each Astro-Tech’s model and focal length are laser-etched into the eyepiece body. The aluminum body material revealed by the etching provides permanent visibility against the body’s black anodized exterior.
All in all, the Astro-Tech AF Series eyepieces offer superb 70° field performance that we feel equals or exceeds the performance of any competitive 68° or 70° field eyepiece, regardless of brand name or price.