Vixen 5mm NLV Eyepiece:
Made in Japan
A few weeks ago I took my first dive into the waters of
Vixen’s new Lanthanum series of eyepieces, the NLV. As far as I can tell, these
eyepieces are the same as the old versions internally, but they do sport “new and
improved” outerwear. Currently, they are priced from $119 USD, come in 11
different focal lengths, and are available from Vixen dealers.
First Sight:
My eyepiece arrived in excellent condition in a well packed
box from an on-line east coast Vixen dealer. Fit and finish is excellent
overall. The coatings appear to me to be excellent, smooth, and free of
defects. Instead of the flip-up rubber eyecup of the old model, the new
versions have twist-up eyecups. The eyecup has two positions that lock into
place. In the lower position it is almost, but not quite flat with the top
lens. Give the eyecup a twist and it rises up about 10 mm and locks into place.
In practice, I find this to be an improved system over flip-up rubber cups,
which to me can sometimes be quite frustrating to adjust. The color scheme is
an attractive black and gold-tone. I have one complaint about the top lens
cover: it is too loose and falls off too easily. The eyepiece has seven
elements in four groups and has a very generous 20mm of eye relief. One element
is made of lanthanum glass. In spite of the number of elements, I find that
this eyepiece is rather small and lightweight, about the same size as my 6mm
TMB Planetary and in fact a bit lighter in weight.
Above: Eyecup retracted and extended.
First Light:
The Vixen 5mm NLV has what I would have to describe as an
excellent image rich in contrast and tack sharp right to the edge. Viewing from
my light polluted suburban yard, I put this eyepiece in my 8”/F6 Dobsonian and
aimed it at the Eskimo Nebula in Gemini. The central star stood out well and
the planetary nebula itself displayed a beautiful round glow with feathered
edges. I was not able to see any filamentation to this planetary but I could
discern the slightly irregular shape outlining the nebulosity. Aimed at the
Great Orion Nebula, the Trapezium stars were very tightly resolved. I could
easily see the E star, and experience tells me that I could also have seen the
F star had the atmosphere cooperated with me, as the air was a bit unsteady. On
a different night, I used this eyepiece in my 102mm F7.75 doublet apo. At 158x
I was able to split Alnitak (separation= 2.4 arc seconds) during periods of
steady air. I would say that light throughput is excellent, and edge of field
definition is very good even in my 80mm F6 achromat. Star colors are accurate
and well saturated.
Lunar performance is very impressive, easily matching or
exceeding the image quality of other eyepieces I have in this price range.
While looking at the Moon I noticed right away that this eyepiece is free of
specks, clumps, and trash inside. I have heard that Vixen enjoys a good
reputation of quality control and this eyepiece lives up that that standard.
This eyepiece is extremely well protected from stray light. When I observed a 5
day old Moon on February 11th it demonstrated excellent contrast
with very little ghosting or flaring. At 7 pm, again using my 102mm apo, I
easily spotted the 9th magnitude star TYC 620-405-1 just off the
dark side of the lunar limb. With the sunlit side positioned just out of the
field of view, I easily followed this star until it disappeared behind the dark
limb about 15 minutes later. I own and have used several eyepieces with a 20mm
eye relief that exhibit some edge of field blackouts during lunar observing.
Although this eyepiece also has 20mm eye relief, I did not find this a problem
at all. With the eyecup extended I could easily place my eye in the right spot
for very comfortable viewing. Those of you who wear eye glasses while observing
will also find this eyepiece easy to use with the eyecup retracted.
Mars is high in the sky in the evening hours but is too far
away to see any real detail with this eyepiece in the telescopes I have. But
Saturn has been a much nicer target. With my 102mm apo, I could easily see the
rings as they crossed the planet, and the shadow that they cast as well. The
Cassini Division was visible at the tips of the rings when the air was steady,
and several bands in the southern hemisphere were visible. Colors are pretty,
with the northern hemisphere showing up a pale violet-gray, the southern
hemisphere as shades of pale golden yellow, and bright pale yellow along the
equator just under the rings. Several moons could be seen, including 11th
magnitude Iapetus. On one morning, 45 minutes before sunrise, the only two
objects left visible in the sky were Jupiter and Venus. Venus was still below
my tree line and I could not observe it. Jupiter was boiling in the morning air
just 14º off the horizon. I was still able to pull out some Jovian detail
though, using my 80mm F7 achromat. The North and South Equatorial bands were
quickly spotted, and as my eye adjusted I could also see some darkening in the
southern hemisphere. The Great Red Spot was not visible at the time.
Considering the lousy conditions I would say that the Vixen did a good job
pulling out detail.
Not too tight:
Some users that do not have motorized or self-tracking
mounts may be a bit apprehensive about the tight 45º AFOV. I also had the same
apprehension as currently all of my telescopes are mounted on “muscle drive”
mounts. I soon found out though that the tight AFOV presented little issue for
several reasons. First, as I mention above, this eyepiece is tack sharp right
up to the field stop, so I can see excellent detail of my target regardless of
where it is in the field of view. Second, the generous eye relief and large top
glass means I can easily see all of the field of view at once. And third, the
true field of view through the telescope was a little bit more than I expected.
I get 240x in my 8” Dob for example, and when I positioned the Eskimo Nebula so
that it would cross the central axis, I can get it to stay in my field of view
for a good 30 seconds. This gives me plenty of time to study my subject before
having to reposition the telescope. Lunar observing with my 102mm apo is an
absolute joy. As the craters, mountains, and plains drift across the field of
view, I really get a feeling of being in a spaceship in orbit. Several times I
watched the crater Posidonius, studying its interior full of rilles and
mountains right up to the point where it disappeared out of the field of view.
Even when Posidonius was halfway out of the field it remained sharp and full of
detail.
Comparisons at night:
The only other 5mm eyepiece I currently own and use is a
Nagler Type 6. Not only does the Nagler have a much wider field of view that is
also well corrected at the edge, but the stars have improved resolution with
slightly tighter airy discs. Other characteristics, image brightness, contrast,
lack of ghosting and flaring, appear to me to be about equal.
I also have a 6mm TS/TMB Planetary and a 6mm Orthoscopic
that I did comparisons with (see photos below). Although it is not entirely a
fair “head to head” as the focal length is different in these two eyepieces, I
can still point out differences in key characteristics. Since most people will
purchase this eyepiece with lunar and planetary use in mind, I decided to do my
evaluation on that same 5 day old Moon of February 11th. Let me
begin by saying that all three eyepieces give, in my opinion, an excellent
on-axis performance on the Moon. I can detect almost no differences in image
sharpness, contrast, and detail. The Vixen and TMB each gave a slightly “warm”
tone to the surface of the Moon, while the Ortho gave a more neutral or “cool”
tone. The Ortho also appeared to me to have a slightly brighter image. All
three eyepieces have excellent contrast with good suppression of unwanted
flaring and ghosting.
Above: 6mm Orthoscopic, Vixen 5mm NLV, 6mm TMB
Planetary.
Above: Another view showing
comparative sizes of top lens.
True field of view: The TMB Planetary is the winner
here as it has the largest true field of view of the three eyepieces.
Eye relief: The Vixen comes out on top. Although the
TMB Planetary also has good eye relief, it is noticeably shorter than the
Vixen. The Ortho has very little eye relief, as I have to put my eyeball right
up to the eyepiece to see anything.
Off-axis lateral color: The Ortho has the cleanest
image off-axis, with no lateral color that I could see. The Vixen is a very
close second, with just a touch of yellow color inside the lunar limb toward
the edge of the field. The TMB exhibited the most lateral color, with the
yellow band being a little more prominent off-axis. The TMB also shows a weird
cyan glow right at the field stop where the illuminated lunar disc is touching
the edge of the field.
Edge of field definition: The Vixen has the sharpest
image at the edge of the field of view. The TMB Planetary is a close second,
and the Ortho as expected from its design shows the most distortion as you
approach the edge of the field.
Image brightness: The Ortho has a noticeably brighter
image, but it is also longer in focal length. I decided to compare the image
brightness with my 5mm Nagler Type 6, to make it an even match in exit pupil.
Globular clusters M10 and M12 (The Gumball) are good targets for testing this,
as they have stars with a variety of magnitudes, right down to the threshold of
my visibility. The Nagler has 8 elements and the Vixen has 7. Looking carefully
at the dimmest starts that I could see with both direct and averted vision,
both eyepieces looked fairly evenly matched to my eye. But if I had to declare
a winner here I’d give it to the Nagler with a slight edge in light throughput.
Ease of use: The Ortho is the clear looser here. Not
only do I have to put my eye right on the top to see anything, I also have to
move my eye around to see the edge of the field. The fact that the Ortho is not
sharp at the edge means I have to move the scope manually more often. And the
photo above shows just how small a hole I am looking through. I find the Vixen
and TMB equally easy to use.
In conclusion:
The Vixen 5mm NLV is an excellent performer in my opinion.
It produced wonderful images in all of my telescopes, from my 102mm/f7.75
apochromat to my 150mm/F5 Newtonian. My only two complaints are the loose top
cap, and the rather slick finish to the barrel and eyecup that make the
eyepiece a bit hard to handle. So which of the above three eyepieces did I find
to be the best? Well, I think the answer to that may depend on which features
the purchaser is putting the emphasis on. For me, I put importance on overall
image quality and ease of use, and my opinion is that the Vixen wins with both
these categories. I am going to be enjoying the views through this eyepiece for
many years to come.
David Elosser
Kernersville North Carolina
