Dave Mitsky's Corner

Tele Vue Radian Reviews

By Dave Mitsky

**2 Reviews, 1 on the 10mm and one on the 8, Order is as follows, 10mm then 8mm review.**

A New Planetary Eyepiece: The 10mm Tele Vue Radian (1998 Review)

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 and have a fair amount of experience with a wide variety of oculars.

Tele Vue Optics has finally officially unveiled the Radian eyepiece, a new line of high quality oculars that is intended to provide adequate eye relief for those who must wear glasses while observing. They will be available in 1999 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 Radians 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 1998 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 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.

The 8mm Televue Radian: Initial Impressions

By: Astronomer Dave Mitsky

I am now the proud owner of a really "rad" Radian, one of three eyepieces that I picked up at the 1999 Northeast Astronomy Forum and Telescope Show on May 16th. I had originally intended to purchase a 10mm Radian (as indicated in my first review) but since I had the opportunity to buy a barely used 8mm from noted amateur astronomer Todd Gross at a very good price I took advantage of it. 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). 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 any other high quality planetary eyepiece of similar focal length.

Addendum (11/29/99): The Tele Vue Radians have been received quite well by the amateur astronomy community. A number of different reviewers have favorably compared the Radians to the world's best planetary eyepieces including the legendary Zeiss Abbe orthoscopics. The only negative comment (and one that is unconfirmed to the best of my knowledge) that I have encountered (via sci.astro.amateur) is that there may be a problem with ghosting in the 5 and 6mm Radians. Since the time I wrote my review of the 8mm Radian I have used the 4mm and 14mm Radians at star parties with excellent results.

On October 16, 1999 I attended the Tele Vue Day at Pocono Mountain Optics where the new 18mm Tele Vue Radian and 31mm Nagler type 5 oculars had their debut. I had the opportunity to have a look through both eyepieces as well as a 17mm and 22mm Nagler type 4 through Tele Vue Pronto and 101 refractors. However, the event was held indoors and my only targets were a dollar bill and a chart of the Messier objects.

* An 18mm Radian was added to the line in late 1999.