Tele Vue Radian Eyepieces

By Chuck Hawks

Tele Vue Radian Eyepieces
Artistic representation of Tele Vue Radian line courtesy of Tele Vue Optics, Inc.

According to Al Nagler, who designed and patented them, Tele Vue's premium Radian line of short focal length oculars is intended to provide long eye relief for those who appreciate or need it, especially eyeglass wearers. The apparent field of view (AFOV) of all Radian oculars is 60-degrees and the eye relief is 20mm. Nagler wrote this about his Radian eyepieces:

"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 1" Tele Vue eyepieces."

Like all Tele Vue oculars, Radians are a proprietary design that is assembled and finished to the highest standards in factories in either Japan or Taiwan that do not make competitive products. 100% quality control is assured; all Tele Vue oculars, whether they are made in Japan or Taiwan, are shipped to Tele Vue's Chester, New York facility for testing. Those sold in Asia are then shipped back to the Far East after quality control inspection in New York.

Here is a chart from Tele Vue with the basic specifications of the Radian oculars:

Type

Model #

Focal
Length
(mm)

Barrel
Size
(in.)

# Elements
/ # Groups

Apparent
Field
of View
(deg.)

Parfocal
Group

Eye
Relief
(mm)

Weight
(lb / oz)

 Radian

 ERD-18.0

 18

 1"

 6 / 4

 60

 B

 20

 0.49 / 7.8

 Radian

 ERD-14.0

 14

 1"

 6 / 4

 60

 B

 20

 0.54 / 8.7

 Radian

 ERD-12.0

 12

 1"

 6 / 4

 60

 B

 20

 0.53 / 8.5

 Radian

 ERD-10.0

 10

 1"

 6 / 4

 60

 B

 20

 0.54 / 8.7

 Radian

 ERD-08.0

 8

 1"

 6 / 4

 60

 B

 20

 0.60 / 9.6

 Radian

 ERD-06.0

 6

 1"

 7 / 5

 60

 B

 20

 0.79 / 12.6

 Radian

 ERD-05.0

 5

 1"

 7 / 5

 60

 B

 20

 0.80 / 12.8

 Radian

 ERD-04.0

 4

 1"

 7 / 5

 60

 B

 20

 0.76 / 12.1

 Radian

 ERD-03.0

 3

 1"

 7 / 5

 60

 B

 20

 0.77 / 12.3

 

Radians incorporate six elements in four groups or seven elements in five groups, depending on focal length. The optical design incorporates expensive, rare earth glasses to optimize performance and minimize aberrations. All air to glass surfaces are fully multi-coated, lens edges are blackened and they have anti-reflection threads for maximum contrast. Ocular upper bodies are made of aluminum for strength and lightweight, while mounting barrels are heavily chrome plated to resist scratching and incorporate a wide safety notch undercut to prevent loss if the scope's retaining setscrew should loosen. They are threaded to accept 1.25" filters.

Radians are finished in a glossy anodized black with a wide, checkered, rubber non-slip band. The bright green Tele Vue name and focal length markings are engraved around the body of the ocular, not screen-printed. They are very attractive and well-finished oculars that practically radiate quality.

Tele Vue Radian 14mm
Radian 14mm Eyepiece. Photo courtesy of Tele Vue Optics, Inc.

Radians come with a soft rubber eye guard to protect eyeglasses from scratches. Protective caps for both front and back to protect the ocular when it is not in use are provided. One of the nicest Radian features is their "Instadjust" click-stopped, push-pull, sliding eyeshade. This helps observers comfortably and conveniently achieve proper eye position, while excluding ambient light. I can attest to the fact that it works and it is the nicest ocular eyeshade system I have used.

The Pupil Guide is another, rather odd, Radian feature. This is a thin plastic disc with a large hole in the center that is placed directly under the Radian ocular's soft rubber eye guard. Its purpose is to help novice, non-eyeglass wearing viewers "zero-in and stay centered on the exit pupil." I have not found it necessary to use the Pupil Guide, but one is included with every Radian eyepiece.

The view through a Radian is sharp from edge to edge with excellent contrast and visual "snap" and no visible distortion. The image quality is excellent and the more you use one of these oculars the happier you will be that you bought it, despite its admittedly high price. (The 2009 list price is $295, but they can be purchased online for about $210 from retailers such as Optics Planet and OPT.)

Remember, all Radians have the same AFOV and 20mm eye relief. From the user's point of view, unlike most ocular designs, it is just as easy to look through a 3mm Radian as an 18mm Radian. Unlike conventional Plossl or Ortho oculars, you can simply buy whatever focal lengths the light grasp of your telescope and the anticipated seeing conditions will support, without concern about tiny exit pupils or eyelash-length eye relief.

I find Radians to be very easy oculars to look through and the 60-degree AFOV is just about perfect. It is wide, yet I can see the entire field of view without having to move my head, something I cannot say about the extra wide 82-degree AFOV of Nagler oculars.

Tele Vue oculars are warranted to the original owner for five years and can be cleaned, serviced or repaired by Tele Vue. They traditionally have a high resale value, should you ever need to sell them. If you are getting the impression that I am impressed by Tele Vue's Radian line, you are correct. They have become my favorite short and medium-short telescope eyepieces and I recommend them without reservation.




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Copyright 2009 by Chuck Hawks. All rights reserved.



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