TeleVue Radian Eyepiece Overview
By Ed Ting
TeleVue's new Radians: (Back) 14, 12, 10, 8, 6 mm
(Front) 5, 4, 3 mm
When TeleVue announced the introduction of these new eyepieces in mid-1998,
my reaction was fairly typical: "Does TeleVue need another line of eyepieces?"
Al Nagler's company had already produced what were arguably the two finest and
most important eyepiece lines in amateur astronomy -the Naglers and Panoptics-
as well as a first-rate line of Plossls. As things stood, the TeleVue eyepiece
line stretched from 4.8 mm all the way up to 55 mm. Any new line of eyepieces,
especially one as ambitious as the Radian project, was bound to result in some
focal length duplication.
Still, TeleVue can apparently justify a new line of eyepieces, based on a couple
First, these new Radians (in mathematics, a radian equals 57.3 degrees, which
equals the approximate field of view in a Radian eyepiece - get it?) feature 20
mm of eye relief across the line. Even the 3 mm will have 20 mm of eye relief.
This has been done before, most notably in Vixen's fine Lanthanum series, but
the Lanthanums have a comparatively narrow FOV (about 40 degrees) and do
show a trace of false color, especially at the edges (they are also a lot cheap-
These new Radians will throw up a wider field of view and manage to be both
sharp and color-free out to the edges.
Also, there is an innovative click-stop eyeguard that extends the barrel of the
eyepiece upwards, allowing eyeglass wearers to preset the levels before hitting
the field. The Pentax SMC-XLs also have this feature, but the Radian's version
is more compact, and, I think, a little more intuitive.
The click-stop eye guard surrounds the entire upper assembly of the eyepiece --
in other words, the part you grab in the dark is the eye guard. The first few
times you pick up a Radian, the weight of the eyepiece sometimes makes the
eyepiece body slide down through the click-stop barrel, convincing you that
you're about to drop something. This took some getting used to.
Finally, the generously large eye lens on all of the Radians appears to be
identical - a neat trick. The 3 mm will have the same eye lens as the 14
Recall that both eye relief and eye lens diameter tends to shrink as the focal
length of the eyepiece decreases, and you will see that TeleVue has apparently
jumped through some optical hoops to bring these eyepieces to life.
These Radians use some standard TeleVue "tricks of the trade." The upper
part of the eyepiece appears to be nearly identical on all of the units. Near the
field lens, there's a barlow-like lens. These are large, heavy eyepieces, but they
don't quite qualify for "grenade" status, and they're not so heavy that you'll lose
your motivation to lug them out night after night.
Several focal lengths are planned, from 14 mm down to a super-short 3 mm.
The price is expected to be around $225-$300 each.
Still, the range of focal lengths of these new Radians sparked some debate
among our group. With 4 mm and 5 mm units planned, does this mean the
4.8 mm Nagler is on the chopping block?
Also, the 14 mm Radian wanders into Panoptic 15 territory, and at about the
same price. They aren't going to sell many 15 mm Panoptics if the extra
eye relief is the same price (short eye relief is a consistent complaint with
the 15 mm Panoptic, which is otherwise an outstanding eyepiece, and one
of my favorites.)
You could make similar arguments about the 6-8 mm Radians/ 7 mm Nagler,
and the 10 mm Radian/ 9 mm Nagler. Time will tell if all of these eyepieces
can coexist in the marketplace.
I briefly looked through these eyepieces indoors at the NEAF in Suffern, and
again at a photo show in Boston this fall. Initial views looked promising.
When the opportunity arose to spend some time with these new units, I jumped
at the chance. Are they as sharp as the Naglers, especially at the edges? How
well does the click-stop device work? Would my beloved 15 mm Panoptic sudden-
ly look inadequate compared to the 14 mm Radian? I was anxious to find out.
Note: As of this writing (Dec 1998) only the 14 mm and 10 mm Radians have
We spent some time with the Radians under clear skies and the moon at first
quarter. The eyepieces were tested in two diverse scopes: my 10" f/4.5 Star-
finder dob, and an Astro-Physics Traveler.
1) TeleVue 14 mm Radian
A very sharp eyepiece. Right away I knew the 15 mm Panoptic would be in
for the fight of its life, and I spent a lot of time in the Traveler, switching back
Conclusions? The Radian is sharper. This is most apparent at the edges of the
FOV. While viewing the Double Cluster, I turned off the RA drive and let stars
drift out of the field of view. They remained pinpoints, even at the field stop.
Also, the field is impressively flat; I noticed none of the pin-cushion distortion
apparent in the Panoptics (although the effect is mild in the 15 mm.) I did
notice some minor kidney-bean black out areas as I moved my eye around.
The Panoptic throws up a wider FOV and seems to have a lot more than its
theoretical 8 degree advantage. The view is more emotionally involving. I
thought the eyepiece was sharp to the edge, until I popped in the Radian,
which did tighten up the stellar images a bit near the field stop.
The Radian's eye relief was impressive, and I could take in the whole FOV
even with the eye guard fully extended. However, since I wear contacts when
I observe, the short relief of the Panoptic doesn't bother me.
Score one for the Radian.
2) TeleVue 10 mm Radian
The 10 mm is an impressive eyepiece - sharp and contrasty, with a flat field.
Again, with the eyecup fully extended, I had no trouble seeing the whole FOV.
I compared the 10 mm Radian to the 9 mm Nagler. The two eyepieces "feel"
totally different, despite being only 1 mm apart. The 9 mm gives a real "Oh
Wow!" feeling as you try to drink in the whole field, while the Radian has a
much smaller FOV. Both eyepieces have some kidney-bean black out areas.
The Radian has longer eye relief, which may be desirable for some users.
I could detect no difference in sharpness or field flatness between them. This
is a high compliment to the Radian, since the 9 mm Nagler is one of the sharp-
est eyepieces made, period. I found I marginally preferred the Nagler, but the
other observer favored the Radian slightly. It felt more "accurate" to him.
Conclusion: Do you need these Radians?
Depends. What do you expect out of your eyepieces?
As the evening wore on, I began to see the an analogy between the Radians
and the Naglers/Panoptics. It is a bit like comparing good Plossls to good
Orthoscopics. Plossls have a wider FOV, and do a better job of convincing
you that you're out in space, looking through a porthole. However, the Orthos
are sharper across what field is there. The comparatively narrow view through
an Ortho tends to be a bit clinical, even a little detached.
Thus, I think fans of Orthoscopics are going to love these Radians. In fact,
they behave a bit like wide-field Orthos. However, those observers looking for
the biggest emotional impact in their views may want to stick with the wider-
field designs and sacrifice a trace of accuracy.
If you already have a set of Naglers and/or Panoptics, and don't need the
additional eye relief, I think it's going to be hard to justify the purchase of
these Radians. On the other hand, if you're starting from scratch, or need
the 20 mm of eye relief, the Radians could go right to the top of your want-list.
In any case, the true strength of the Radian line may lie in the shorter focal
length models. If the 3 mm and 4 mm units are as sharp and comfortable as the
10 mm and 14 mm units tested here, they could be really special. Watch this
space for updates.
Update, 11/99: I am often asked by readers to comment on the other models
in the Radian line. Luckily, there is very little to say. Unlike the Naglers
and Panoptics, which have markedly different characteristics within the line,
the Radians seem to be engineered for uniformity. One feels pretty much the
same as the next.
The shorter focal length units (the 3 mm, 4 mm, 5 mm, and 6 mm) are
somewhat longer and heavier than the rest of them. Otherwise, you'd have
difficulty telling them apart. Contrast this to the huge difference between,
say, the 4.8 mm and 20 mm Naglers. This uniformity can be appealing, and
at least one observer I know has gone ahead and replaced his Naglers with
a new set of Radians.
An 18 mm unit was announced in October of 1999. This is muscling in on
the territory of the 19 mm Panoptic, one of the truly great eyepieces of all
time. I'll report back when I can compare the two.
End Radian Eyepiece Overview
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