Vixen NPL Plossl Series

The New Vixen NPL Plossl Series

It seems like everything is getting a design makeover these days, from automobiles to washing machines, and everything in between. It’s nothing new, really. But Vixen has taken the “old fashioned” Plossl eyepiece and given it a new face lift that almost takes it beyond recognition for this type of eyepiece design. I had my doubts when I got my first 20mm NPL with a Vixen telescope I ordered, but I quickly appreciated the quality and workmanship built into this eyepiece. I therefore purchased the rest of the set, which includes: 40mm, 30mm, 25mm, 20mm, 15mm, 10mm, and 6mm.

The Chinese manufacturer has, in my opinion, come up with a nice ergonomic design. The fit and finish is excellent across the series, and the coatings are well applied and uniform. Each eyepiece is easy to grasp and handle. I purchased these eyepieces from an east coast Vixen dealer and they all arrived in excellent shape. (Note: the coatings are all the same from eyepiece to eyepiece, but they look different in one of my photos.) The 40mm through 20mm have twist-up eyecups. They are 2-position, clicking into position when extended. In the 40mm through 25mm, they are comfortable to view with eye glasses on. If you do not wear glasses the extended position places the eye in a comfortable viewing position. The 20mm has too little eye relief to be used easily with eye glasses on, and I don’t know why they put the adjustable eyecup on this one. Extending the eyecup on the 20mm does not in my opinion improve the viewing comfort although some might prefer this. The photo below comparatively shows the sizes of the top lenses.

Below is a photo showing the relative positions of the eyecup retracted and extended.

Below: looking through the business end of the 30mm Plossl.

At first glance, they may look like heavy, bulky eyepieces, especially for a simple 4-element Plossl design. Actually, the 40mm, which is the largest of the series, weighs in at about 135 grams, or 4-3/4 ounces. This is nearly 2 full ounces less than my Meade 40mm

Plossl, pictured below with “typical” Taiwanese made 25mm and 9mm Plossls (rear) and the Vixen 40mm, 25mm, and 10mm in front. All seven Vixen NPL eyepieces fit nicely in my Orion eyepiece fanny pack and I barely know I’ve got it hanging around my waist.

Okay, so what about the views? Well, to start with, these are 4-element Plossl designs, and like other Plossls they have rather poor edge of field performance at the longer focal lengths and eye relief is tight for the shorter focal lengths. The 30mm gives me 19x in my 3.3” F/6.9 apo refractor, and this very nicely frames Sulafat and Sheliak in Lyra at opposite ends of the field, with a tiny but easily seen Ring Nebula (M57) in the middle. The stars in the middle are very sharp and well defined. But Sulafat and Sheliak are extended into short streaks parallel to the edge of the field. The dimmer the stars, the less you notice this effect, and edge of field performance improves with both the shorter eyepiece focal lengths as well as longer telescope focal ratios. I find the overall performance of sharpness, color accuracy, and contrast to be consistent throughout the focal range. (Only the 6mm showed one issue that I will go into later.) Light throughput is very good. With the 30mm in my little Vixen 95L Mak, I was able to see the Leo Triplet under dark skies, including NGC 3628, all in the same field of view. The medium focal lengths are great for more magnification and contrast on deep space objects, and the 10mm and 6mm show excellent lunar and planetary images.

One August evening I went on a deep space tour with my 3.3” apo refractor. The 40, 30, and 25mm are excellent for scanning the skies in Sagittarius country. Nebulosity in the Trifid, Lagoon, and Omega nebulae show up well with the 25mm, although the Trifid is really quite dim from my suburban front yard. Globular cluster M15 showed a bright core with halo in the 15mm (39x). M11, the Wild Duck cluster, is framed beautifully in the 20mm with its surrounding star field. The 10mm easily shows the stars and dark lanes in this eye catching open cluster. The nearby globular cluster NGC 6712 is an easy star-hop in the 30mm, just 2.5º to the south of M11. Although it has a low surface brightness I was able to spot it at 19x in the 30mm and it was visible in all eyepieces up to 10mm. The toughest deep space target I nabbed that night was the 11.3 magnitude NGC 6629, a planetary nebula in Sagittarius. Once I located the exact position, it was just inside my averted vision range with the 6mm at 97x. The 6mm also showed a nice view of M57, the Ring Nebula in Lyra. Although dim in my 85mm refractor, its doughnut shape was obvious with steady skies and I could just detect a brightening around the edge of the Ring.

I would give a high score in resolution to these eyepieces. All focal lengths show very tight stars, with excellent contrast in the background sky and sharply defined airy discs. The 6mm is an excellent star splitter. Under steady skies in my 3.3” apo for 97x, the Double-Double in Lyra was easily split into all four components, and Izar in Bootes with it’s 2.4 arc seconds separation looked like two miss-matched colorful marbles with a hairline of black sky separating them. With Orion low in my early morning sky, the 6mm showed 5 stars in the Trapezium.

I like the color accuracy in these eyepieces, which is consistent across the focal range. Vega in my little apo showed a pure white image with all focal lengths. Jupiter is quite colorful under clean steady skies, from the brick-red of the North Equatorial Band to the creamy whites of the zones. Scanning 4 degrees ENE of Kornephoros in Hercules with the 25mm, I easily spotted the pale turquoise color of NGC 6210, the tiny Turtle Nebula.

Toward the end of August, I tested all of these eyepieces in my 8” F6 Dobsonian using Jupiter as a target, looking for reflections, ghosts, or flaring. Starting with the 40mm and working my way up in power, every eyepiece showed excellent sharpness on axis and the image was clean and free from any unwanted reflections or ghost images, with one exception, the 6mm. At 30x, the 40mm eyepiece resolved Jupiter into a tiny but well defined disc free of distortion. By the time I got to the 15mm (80x) I was beginning to see some good band detail on Jupiter’s disc. The 10mm (120x) showed the best view at the time, due to seeing conditions that were less than optimal, showing multiple bands and good detail in the two equatorial bands. I could see where the SEB began a split into two parallel halves, and a few dark knots could be seen on the NEB. The 6mm, giving me 200x, was just a bit too powerful for conditions, but being patient the eyepiece showed the same details as the 10mm during short periods of steady air, with a larger image scale. The 6mm does show one minor fault. I can see a dim ghost image of Jupiter in the field, on the opposite side of the center axis point. It shows up as a very dim round patch of light but soon becomes non-distracting.

Lunar observing is a pleasure with all of these eyepieces. Even the 40mm and 30mm show very little flaring through the eyepiece when the full Moon is placed just outside of the field of view. The middle focal lengths give a very sharp medium power view of the Moon along with any nearby stars that happen to be bright enough to be seen in the Moon’s glare. These eyepieces are good tools for doing one of my favorite pastimes, watching the Moon occult dim stars behind the limb. Using my 4” doublet apo on the evening of September 12^th, I watched the Moon occult Neptune. The Moon was nearly full (12.4 days into the lunar cycle) and both the 10mm and 6mm easily showed 7.8^th magnitude Neptune as it disappeared behind the Moon’s limb. Neptune’s subtle turquoise color was a lovely contrast to the brilliant light of the Moon. About an hour later, Neptune reappeared on the bright side. Although I was not able to catch the exact moment of reappearance, I first spotted the planet when it was just 1 arc minute from the bright limb. The 10mm and 6mm show great lunar detail at high power. The 6mm in my 3.1” achromat showed the Triesenecker and Hadley Rilles when the sun and shadows were at the proper angles. The lunar limb with the 10mm is tack sharp, as if carved out with a razor blade. Mountains in Mare Orientale show up in relief along the western limb after a full moon. The contrast in these eyepieces easily shows subtle variations in albedo features in lunar mare during a full moon. One nice characteristic of these eyepieces is that lateral color is almost non-existent in all focal lengths, with just a hint of yellow color inside the bright lunar limb at the extreme edge of the field of view.

So how do these Vixen NPL’s stack up to other types or brands of eyepieces? I have several of the Vixen NLV Lanthanum eyepieces, and when I compare similar focal lengths the Lanthanum’s do exhibit better edge of field performance, overall sharpness and contrast, as well as much better eye relief. Premium brands of eyepieces like my Televue Type 6 Naglers or Pentax 20mm and 28mm give a much wider field of view, better eye relief, and of course the legendary sharpness at the edge of the field. Although the Vixen 15, 20, and 25mm NPL’s are very sharp on-axis, they do not quite match the sharpness of my Televue Plossls. The visual performance of the 10mm and 6mm is virtually identical to my orthoscopic collection in that focal range, but with a sharper off-axis view.

My two biggest issues with these eyepieces are the 6mm’s dim ghost image of Jupiter, and the fact that the longer focal lengths are not as par-focal with the shorter ones as I would like them to be. Well, there’s a third; I feel like there’s too wide a gap between the 10mm and 6mm focal lengths. You can, of course, Barlow the 15mm to get there, but doing so may degrade the image with increased glare. I would prefer that they included a 7.5mm or 8mm in the lineup. But overall, my opinion is that Vixen has come up with a really nice design. They are well made, the design is ergonomic, and I give them a high rating for image quality. All of this is put into an attractive package. At prices currently starting at under $40.00 each, these are in my opinion an excellent choice for the budget-minded astronomer.

David Elosser

Kernersville NC