The Astro-Tech 1.25” Flat Field eyepieces provide exactly what their name implies, a flat field of view that keeps stars and planets in sharp focus from one edge of the eyepiece field to the other. There is no need to constantly refocus to keep the image sharp as an object drifts across the field, a virtue that Dobsonian owners will particularly appreciate (but a visual virtue all telescope owners will enjoy).
Each uses five lenses in a proprietary design to provide a flat field of view ranging from 53° to 65°, depending on the focal length. All Astro-Tech Flat Field eyepieces are parfocal, to minimize the need for refocusing when you change eyepieces. The edges of their lenses are blackened and the interiors of the barrels 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 Flat Field eyepiece has a twist-up rubber-rimmed eyecup for eyeglass use. Twist it clockwise to fully retract the eyecup for use with eyeglasses. Twist it counter-clockwise to extend the eyecup. This helps shield your non-eyeglass wearing eye from ambient light to improve the image contrast. The eyecup also can be partially extended to any intermediate height to position your eye for the most comfortable observing.
The focal length of each Astro-Tech Flat Field eyepiece is laser-etched into the eyepiece body. The aluminum body material revealed by the etching provides permanent visibility against the body’s black anodized exterior. Rubber grip rings on the barrels of all focal lengths 12mm and above provide a sure grip when wearing gloves or mittens in cold weather. Protective dust covers are provided for both ends of each eyepiece.
A safety groove is machined into each barrel. This engages the thumbscrew or compression ring of your star diagonal or focuser drawtube to keep the eyepiece from falling should the thumbscrew accidentally loosen during use. In addition, the barrel is threaded to accept standard 1.25” color and light pollution filters.
Priced well below similar designs from other suppliers, and available from Astro-Tech in a wider selection of focal lengths than available elsewhere, the Astro-Tech Flat Field eyepieces offer premium performance at an affordable price. They are typical of Astro-Tech’s “more performance for less money” philosophy.