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Vixen 5mm NLV: Made In Japan

Posted by david elosser   02/22/2008 12:00AM

Vixen 5mm NLV: Made In Japan
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 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: Eye cup retracted (left) 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 have never been 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. Allowing for the unsteady air I suffered that night, 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. On a different night, I used this eyepiece in my 102mm F7.75 doublet apo. At 158x I was able to split Alnitak 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 equally 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 an issue 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.

Planetary viewing is a bit frustrating for me right now. 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. I did get one good look at Saturn one morning with my 102mm apo. I could easily see the rings as they crossed the planet, the Cassini Division was visible at the tips of the rings when the air was steady, and one prominent band in the southern hemisphere was visible. Several moons could be seen, including 11th magnitude Iapetus. On another 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 shows the most distortion as you approach the edge of the field.

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. 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