Caveat: The following is a completely subjective review.  I am by no
means an expert on eyepiece optics but I do have a working knowledge of
the basic concepts.

Tele Vue Optics has finally officially unveiled the Radians, a new line
of oculars that is intended to provide adequate eye relief for those who
must wear glasses while observing.  They will be available next year in
focal lengths of 3, 4, 5, and 6mm (7 lens elements) and 8, 10, 12, and
14mm (6 lens elements).

Like the Tele Vue Panoptics expensive high index lanthanum glass is used
in the manufacture of the Radians.  These eyepieces will have a 60
degree apparent field of  view, a well designed eye lens, and a generous
20mm of eye relief.  The 1/2 pound Radians will all be the same price,
somewhere between the cost of a 15 and 19mm Panoptic, and should be
binoviewer friendly.  They seem destined to compete with the Pentax SMC
XL's in the wide-field planetary eyepiece race.

The pincushion distortion (i.e., lack of image linearity) that is
inherent in the Panoptic line has been virtually eliminated in the
Radian line by the use of a Nagler style negative lens system (i.e., a
"built-in Barlow lens").  Some apparent field of view was sacrificed to
produce longer eye relief.  (The name Radian springs from the fact that
Mr. Nagler had originally planned a 57 degree apparent field of view and
that one radian equals 57.3 degrees.)  A smoothly functioning 8
click-stop "Instadjust" eyecup allows proper positioning of the eye.

I have had three opportunities to inspect the 10mm Radian.  The first
was at the Northeast Astronomy Forum and Telescope Show, which took
place in Suffern, New York on May 3rd.  The 10mm Radian, unlike a 15mm
Tele Vue Panoptic, exhibited no noticeable pincushion distortion on an
indoor target when viewed through a 85mm Tele Vue refractor.  The image
quality was quite good.  Intriguing, but how would the Radian perform
under starry skies?

Two few months later at the 1998 Stellafane convention I learned the
answer to that question.  I spent some time on both Friday and Saturday
nights observing with "Uncle" Al.  On Friday I had some very impressive
views of M31, M32, M110, and M13 through a 85mm Tele Vue refractor and
the Radian.  The sharpness of the field and lack of pincushion
distortion were quite evident.  When I positioned M13 so that only half
of it was visible, the stars of this great globular cluster were tack
sharp at the edge of the field.  The Radian's contrast was excellent.
The next night I observed Jupiter and Saturn through a Tele Vue 140
refractor, the Radian, and a Tele Vue 2x Barlow lens.  Although the
magnification was only in the 150x range, planetary performance seemed
very good indeed.  I noticed no obvious ghosting.

On October 3rd I attended the annual Tele Vue Day at Pocono Mountain
Optics near Moscow, Pennsylvania.  A number of Tele Vue refractors were
set up for daytime outdoor viewing and the 10mm Radian performed very
well visually.  One interesting result of an eyepiece comparison between
the Radian and an 18mm Meade SWA was the fact that the apparent field of
view of the SWA (supposedly 67 degrees) was almost identical to that of
the Radian.  A bit later Mr. Nagler discussed the design principles of
the Radian, Panoptic, and Nagler lines with me at length.

Amateur astronomers from throughout the nation have been discussing the
new Radians on the sci.astro.amateur newsgroup.  Joe Castoro reported
that he saw the 10mm at the NEAF and that it had a well corrected field
with exceptional contrast.  Robert Cuberly used one at the Texas Star
Party and was impressed with the flat and very sharp field.  Thomas Back
did a rough field test at Pocono Mountain Optics and admired the
Radian's highly corrected field and lack of distortion.

Judging from what I have seen and heard of the 10mm Radian I will be
replacing my 10.5mm Tele Vue Plossl with one in a few months time.
 
2. The 8mm Televue Radian: Initial Impressions

I am now the proud owner of a "really rad" Radian, one of three
eyepieces that I picked up at the Northeast Astronomy Forum and
Telescope Show on May 16th.  Despite the curse of recently acquired
astronomical equipment I got to try out my new 7mm Tele Vue Nagler and
8mm Radian on the same day of  purchase.  The eyepieces were used with a
114mm f/7.9 C4.5 and a 6" f/10 ATM Dob at my residence that Sunday
night.

My views of Mars were quite good through the 6" Dob and 8mm Radian
(190x), as were those of a number of binary stars including Gamma
Virginis.  I even caught some glimpses of Niliacus Lacus through the
4.5" at 225x (8mm Radian and 2x Ultima Barlow lens).

While comparing eyepieces of different focal lengths is a tricky
business I felt that the Radian produced better planetary views through
the 6" than did the 7mm Nagler (218x).

The following night (5/18/99 UT) I tested the 8mm Radian using the 12.5"
f/6.5 Cave Newtonian reflector at the Astronomical Society of
Harrisburg's Naylor Observatory (http://www.ezonline.com/ash/obs.htm).
Mars was superb at 258x through the 12.5" Cave and Wratten #21, 25, 30,
and 80A color filters. The central meridian was about 326 degrees at the
time and I had my best ever view of Sinus Sabaeus on the preceding
limb.  The NPC, which has reportedly grown considerably of late, was
fairly prominent.

Comparing the Radian to an 8mm Brandon, I saw little difference in fine
contrast between the two eyepieces but a large difference in the two
fields of view.  (That is to say that disregarding the difference in the
fields of view Mars appeared very similar in both oculars.)  There was
noticeably more lateral color at the extreme edge of the field in the
Radian, however.

The sliding Instadjust eyeguard takes a little getting used to but works
quite well.  It is very effective in reducing blackouts.  Using the
Instadjust at full extension had the effect of reducing the Radian's
field of view rather dramatically.

I also looked at a number of bright deep-sky objects using the Radian.
M3, M5, and M13 stood up to the high magnification nicely.  The fine
open cluster M11 was simply outstanding at 258x through the 8mm.
Galaxies such as M51 and M104 did not fare as well. Nor did the Dumbbell
Nebula, M27.  I should mention that while the seeing was rather good
transparency was not.

Stars were very sharp right to the edge of the field.  The Radian also
did a nice job of resolving some close binary stars such as Epsilon
Bootis.  And I was able to see the dim glow of 13.7 magnitude Pluto
through the Tele Vue eyepiece.

On the following Tuesday evening at 22:05 UT I put the 8mm Radian to
work viewing the sun under better than average conditions.  When used
with my C4.5 the Radian (112x) produced a larger image of the solar disk
than I am used to when I make my solar observations, which are usually
done at 53x (17mm Tele Vue Ploessl).  One of the sunspots that were
visible was quite large and was seen in very sharp detail.  The ample 60
degree apparent field of view of the Radian allowed the entire solar
disk to be observed with some minor adjustment of the telescope's
position.

It will be interesting to see how favorably my new Radian compares to a
7.5mm Pentax SMC XL, 7.5mm Takahashi LE, 8mm Tele Vue Ploessl or other
high quality planetary eyepieces of similar focal length.

Dave Mitsky
ASH, DVAA