60° Apparent Field Eyepieces
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Concept: In 1979, I had to sacrifice size, cost and weight in the original Nagler design to achieve what were previously mutually exclusive interests; extremely wide field, full field sharpness and comfortable eye-relief. Fortunately, users agreed that a lifetime of "spacewalk" viewing pleasure justified the investment. Fast forward to 1999. As the hobbyist population ages (along with me), more amateurs need eyeglasses. It was time to adjust the mix of parameters for observers who require or prefer long eye-relief. Under the framework of the "Nagler" design, the new field was set at 60° with a uniform 20mm eye-relief. Optimizing this new design with fully multicoated exotic glasses, we reached our new goal of full field sharpness with true orthoscopic linearity, highest contrast for critical planetary viewing, and compact size. The size and weight blend also makes the Radian preferable for small instruments and bino-viewers, and allows the convenience of being parfocal with other 1¼" Tele Vue eyepieces. — Al Nagler
Instadjust was developed for maximizing contrast while aiding in proper eye positioning for non-eyeglass wearers. It is essential, since with the Radian's long eye-relief, non-eyeglass wearers could easily get too close to the eyepiece, resulting in vignetting where edge field rays miss your pupil. The push-pull, click-stop adjustment permits fast positioning and maximum suppression of environmental stray light.
Another unique development is the Pupil Guide. It helps non-eyeglass wearers, especially novices, zero-in and stay centered on the exit pupil. The Pupil Guide is included with all Radian and Nagler Type 4s and fits under the soft, fold-down rubber eyeguard.