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Tele Vue 1.25" Radian Eyepiece - 4mm

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Brand TeleVue
Part Number ERD-04.0

Product Info

Manufacturer Description

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.

All Tele Vue eyepieces have proprietary tuned full multi-coatings, blackened lens edges, high index glasses, fold-down eyeguards, rubber grip rings, cover for the eyeguard, an undercut in the barrel for extra locking security, and filter threads. All Tele Vue eyepiece lines are proprietary, in-house designs manufactured to their specifications and tolerances. Every eyepiece is individually tested at Tele Vue to ensure it meets high optical and cosmetic standards.


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Apparent Field of View 60°
Barrel Size 1.25" (31.7mm)
Bolt Case Included Discontinued Item
Bolt Case Size Agena 65x120mm
Coatings Fully Multi-Coated
Max Width 1.8" (45.7mm)
Eye Relief by Design 20mm
Field Stop Diameter 4.2mm
Filter Threads Standard 1.25" Filter Thread (M28.5 x 0.6)
Focal Length 4mm
Lens Elements 7
Lens Groups 5
Parfocal Yes
Rubber Eye Guard Yes
Blackened Lens Edges Yes
Additional Information

- Suitable for use with Tele Vue Bino Vue binoviewer
- Suitable for use with Tele Vue Dioptrx / digiscoping

Manufacturer TeleVue
Eyepiece Focal Length 5mm and Under
Eyepiece Field of View 51 - 60 degrees
Eyepiece Series Tele Vue Radian
Barrel Type With safety undercut
Eyepiece Weight 12.10oz (343.03g)