TeleVue Radian eyepieces have six or seven lens elements, depending on the focal length. They make ideal planetary and general purpose eyepieces, and are very relaxing to use with glasses, as the distance from lens to eye or "Eye Relief" is 20mm throughout the whole range.
Instadjust was developed for maximizing contrast while aiding in proper eye positioning for non-eyeglass wearers.
It is vitally important, since with the Radian's long eye-relief, non-eyeglass wearers can 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.
An additional unique development is the Pupil Guide which aids 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.
The size and weight blend of these Radian eyepieces make them preferable for small scopes and bino-viewers, and have the added convenience of being parfocal with other 1 ¼ inch Tele Vue eyepieces.
"What sets Radians apart from other long eye-relief, short-focal-length eyepieces is superb image quality. Even discerning planetary observers who customarily choose Plössl or orthoscopic designs are switching to Radian." - Sky & Telescope, December 1999