The TeleVue 5mm Radian - Round One
TMBack
eyepiece. This eyepiece was purchased at full price from Pocono
Mountain Optics, and was in no way a hand picked unit (even know
I am friends with both Al and David Nagler).
This is the first of a series of three tests, the first with my
new Astro-Physics 130mm f/8.3 EDT, the second and third with be
with my Orion Short Tube 80mm and lastly my Astro-Physics 180mm f/9
EDT.
The eyepiece is rather attractive compared to its main competition,
the Pentax 5.2mm XL. I find the Pentax much bulkier, and more difficult
to use in a binoviewer. Unlike some other observers, I find the new
TeleVue lettering an improvement over the old style lettering. It makes
the eyepiece easier (at night) to see what the focal length is, and
accents the look of the eyepiece nicely.
I first checked the eyepiece for coating and cosmetic flaws, and
happily, found none. However, there was some dust and a small spot on
the inner field lens (not the negative lens group). I unscrewed the
eyepiece (I do not recommend that anyone do this, unless they have the
necessary experience to internally clean an eyepiece, and believe me,
unless you do, you will make matters much worse -- contact TeleVue if
you have any problems). Using a Chemtronics Ultra Jet duster, their
cleaning swabs, and HPLC grade Acetone, I was able to clean the eyepiece
to clean room conditions.
Next are the coatings. They are different from any other I have seen.
The negative lens group has a very dark red/violet coating, and the
eyelens has a very dark blue/violet coating. Actually, the color of
the coating is not that important, what is important is the amount of
light that is transmitted, and not reflected back. In this regard, the
coatings on the Radians are the best in the history of TeleVue. Using
a Wratten #58 filter, on axis, the amount of reflected light was on par
with the best eyepiece coatings. BTW, this is the way to test anti-
reflection coatings by eye, using either a deep green or deep yellow
filter with a bright light source behind the eyepiece, and viewing the
reflection on axis as much as possible. This will show the true
transmission of the coating in the critical peak visual wavelengths.
So, don't judge a coating just by its color.
This particular Radian's Instadjust eyeguard did not slip down as I
picked the eyepiece up, unless I did it quickly. The click stops feel
just right to me. As I don't wear glasses, I found the 20mm eyerelief
just splendid, and with the Instadjust eyeguard set at three clicks
from the top, I found absolutely no "blackouts," and wonderful full
field viewing with great comfort. I think that the blackout problem
mention by some is just a symptom of not adjusting the eyeguard right.
Now, on to the testing. The night was one of very good seeing, and
good transparency. Using a new Astro-Physics 130mm f/8.3 EDT and
Maxbright diagonal, I had my 4mm and 6mm Zeiss Abbe orthos, 5mm
Nikon Abbe ortho, the 5mm TeleVue Radian and 7mm Nagler. All
eyepieces are in new condition, and were carefully cleaned to make all
tests fair.
My first test subject was Mars. Seeing was a "6" with moments of 7
or better. Syrtis Major, Iapygia, Sinus Sabaeus, Hellas, Oxia Palus
and the NPC was in view. Numerous other fine details were visible.
The 5mm Radian (217x) was the first eyepiece tested. Limb sharpness
was outstanding, as the image had "snap." Contrasts were likewise very
high, and the planet looked beautiful. I said to myself, this seems like a
high quality planetary eyepiece! But was I just being fooled?
Next eyepiece was one of my all-time favorites, the 5mm Nikon. I
have used this eyepiece to see the greatest amount of detail on Mars
through my 7.1" EDT. It is unmatched for planetary observing at the
5mm focal length. The image of Mars was almost identical! I switched
back and forth, but after about a dozen times I had to come to the
conclusion that the Radian was in the same class. Now there were
differences to be sure. The very lowest (and only visible under the
best seeing) contrast features were slightly better in the Nikon.
But it took some real straining to see this. However, the Radian was
(unlike some reports) sharper! There was no question that the focus
was ever-so-slightly more definite in the Radian, than in the Nikon.
You may ask, well, why wasn't the Radian the best in all aspects?
Well, because of the slightly greater scatter. The most severe test of
scatter in an eyepiece is to view a bright object, and use averted
vision to see the diameter and intensity of the scatter around bright
objects. But this scatter is not just from the eyepiece. It comes from
atmospheric scattering, the main optics, and secondary optics, a
diagonal (if one is used), the eyepiece and finally your own eye. So,
you will never see a totally scatter free image of a bright object
against a black sky.
The Radian showed about a 150 arc-second scatter circle around Mars
using adverted vision. The Nikon and Zeiss eyepieces showed about a
120 arc-second scatter field, with about 15% less intensity. Now don't
jump to conclusions, 15% is just over the threshold of visibility, and
without very low scatter optics on a good night, no differences could be
discerned between the two eyepieces. The Radian is much better (read
less) in the scatter department than the Pentax 5.2mm XL, which I found
objectionable for planetary viewing.
But the greater sharpness in the Radian made up nicely for the added
scatter vs. the Nikon. The verdict on Mars? The 5mm Radian is a first
class planetary eyepiece.
On to M13. It was wonderful view, considering that the Moon was still
in the sky (albeit low and in a waning stage). The 5mm Radian framed the
globular beautifully, and resolved stars across the core. The Nikon was
no match for the view with its 40 - 42 degree field. If the Nikon was
going deeper, magnitude wise, it was very hard to tell. Seeing had a
greater effect on the visibility of the faintest stars, than eyepiece
differences. If push came to shove, I would give the advantage to the Nikon
in seeing slightly deeper, but the view was much more esthetically pleasing
in the Radian.
Then on to Vega. The two faint stars close to Vega once again
confirmed the scatter differences. But the visibility of these stars
were equal in both eyepieces. I also tested the astigmatism, distortion
and lateral color of the Radian using Vega. At f/8, astigmatism was as
well corrected as the Nagler eyepieces, which is to say, I could follow
the Airy disk from the center of the field to the very edge of the
field -- excellent! Distortion was not detectable. Maybe a daytime test
would show a very small trace, as my daytime 10mm Radian test showed.
In any event, this design can truly be called "orthoscopic" in the
distortion department. The only noticeable aberration in the Radian
eyepiece is lateral color. Again, at f/8, none could be detected on a
bright star until the 25-degree half field (50 degrees). The last 5
degrees do show noticeable lateral color, but only on bright stars.
This is hardly a problem; one will never notice it in star fields, and
on bright objects, one always centers the object anyway.
Finally, I viewed Mizar/Alcor with the 5mm Radian eyepiece. This,
simply put, was the best view of this double (triple) star I have ever
seen. With the Nikon, I could not view all three stars at once.
Some final words. The 5mm Radian surprised me with its superb per-
formance. The sharpness, lack of internal reflections, high contrast,
high light throughput (remember this is a 7-element design), ideal
eyerelief, comfort, large usable field, and corrections of field
aberrations, puts it in an unique class. While I won't be selling
my Zeiss, Pentax and Nikon orthos, for viewing of all types of objects
(and that includes lunar and planetary), the Radian has the best
combination of performance and features of any eyepiece on the
market.
Next, we will see how the Radian performs with the Orion Short Tube
80mm at f/5.
Thomas Back
Gerh3150
to other EP one might consider...good show!
Chris Gerh...@aol.com
Shedir
Great review Thomas. Now we need a full review of the new AP 130 f/8.3
from you as promised :)
Shedir
Gerh3150
Chris Gerh...@aol.com
cala...@my-dejanews.com
gerh...@aol.com (Gerh3150) wrote:
> esp. how the F8.3 version differs from the EDF version...
> Chris Gerh...@aol.com
>
Thanks for providing the excellent review. I look forward to round 3.
Craig
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TMBack
>Great review Thomas. Now we need a full review of
>the new AP 130 f/8.3 from you as promised :)
Thanks. As for the AP 130mm f/8.3 EDT review, that
will be in the making.
>esp. how the F8.3 version differs from the EDF version.
Thanks Chris. Don't have a f/6 EDF on hand. You will
have to ask Robin Casady, he has both.
>Thanks for providing the excellent review. I look
>forward to round 3.
>
>Craig.
Thanks Craig.
Thomas Back
Chuck Gulker
myself. I've got the 14 and like it very much.
Take care, Chuck
AndersonRM
(TMBack) writes:
> Finally, I viewed Mizar/Alcor with the 5mm Radian eyepiece. This,
>simply put, was the best view of this double (triple) star I have ever
>seen. With the Nikon, I could not view all three stars at once.
What is the field of view in the Radian 5mm? I get 16minutes
based on your scope and the apparent field of
57.5 deg in the Radian. Alcor and Mizar are 11.8 minutes apart,
so all three stars should have been visible.
Good report, BTW. My 8mm Radian seems very good for planets
as well, but I'm still comparing.
-Rich
Even now, after the damage is revealed,
Clinton still refuses to implement controls
to keep the U.S. more secure. He is
"The Atomic Prostitute."
edw...@my-deja.com
Great report.
ed
In article
tmb...@aol.com (TMBack) wrote:
> As promised, here is my review of the new TeleVue 5mm Radian
> eyepiece. This eyepiece was purchased at full price from Pocono
> Mountain Optics, and was in no way a hand picked unit (even know
> I am friends with both Al and David Nagler).
.....
Sent via Deja.com http://www.deja.com/