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Home > Reviews > Eyepieces > Other > William Optics UWAN Eyepieces – 4mm, 7mm, 16mm

William Optics UWAN Eyepieces – 4mm, 7mm, 16mm
By Timm Bottoni - 4/16/2007

The UWANs side by side.

I didn’t plan on buying ultra wide angle eyepieces – in fact I was very happy with TV plossls which are great eyepieces, but after I got the WO (William Optics) EZTouch mount, I found myself searching for things manually and enjoying it. I liked the combination a lot – it was fast to setup, smooth and just plain fun to use, but the mount does not track, so I found myself running out of sky quickly with 50mm deg field of view (FOV) plossls.

Why I started looking for ultra wide field eyepieces

I started reading about wide field eyepieces, the big ones, the “space walk experience” ones, the ones that cost as much as many small telescopes and I soon realized I just couldn’t afford to spend $300 to $500 per eyepiece for the Televue Naglers or Panoptics. I already had a WO 33mm SWAN, a fairly decent 2” economy wide field eyepiece with a 72 deg FOV which yields over 4 degrees of sky, but I wanted something wider, and higher magnification and a little better quality. While nice, the SWAN was not sharp to the edges in my F/6.9 WO 80mm FD APO refractor, and for a 33mm eyepiece, providing 17X in my scope, this was OK, but for the higher powered eyepieces I was willing to spend a little more in hopes of getting sharp to the edge, wide field views..

I figured that with my light pollution, I would be best off with the widest fields of view possible and higher magnifications – so after a couple of books, a few emails to some trusted friends, and a couple of reviews to convince me, I bought a 7mm WO UWAN to try and see how I would like it. Several months later, the 16mm UWAN followed, and finally the 4mm UWAN was the last of the 1.25 inch eyepieces that WO offered in the series.

What is a UWAN?

William Optics currently has a number of eyepieces that they manufacture in Taiwan, including the SWAN series, that provides a 72 deg FOV, and the UWAN series that provides an 82 deg FOV. The UWANs currently come in 1.25 inch sizes of 16mm, 7mm, and 4mm, and also a 2 inch model at 28mm. The 4mm, 7mm, and 16mm models each consist of 7 elements, in 4 groups, according to the WO website, and each offers about 12mm of eye relief. They are parfocal with each other, meaning that you can switch eyepieces without having to refocus. The UWAN eyepieces each offers a number of features including a soft rubber twist up eye cup, a smooth tapered safety cut barrel, rubber knurled gripping, WO labeled end caps, fully multicoated optics, and a two year warranty. Upon examination, it appears that each eyepiece has an initial lens assembly, that can be seen if the barrel section is unscrewed, followed by the field stop and the remaining main glass in the body of the eyepiece. I didn’t try to disassemble them, it would have likely proved disastrous, so with the exception of unscrewing each barrel assembly to peek inside, I made no attempt to dig any deeper into the design. The barrel assemblies are all different in sizing and threading, and do not have any interchangeable parts. I thoroughly examined each eyepiece from the outside, checking the quality of the glass and coatings, the quality of the machined parts, and the overall fit and finish.

A Hands On and Practical Review of the eyepieces

This is not a scientific review; it contains no direct comparison to any other brands of Ultra Wide Field eyepieces. In fact, the one thing I have come to realize about eyepieces is that what each person chooses is very dependant on their scope, their eyes, what they like to view; in general, eyepiece preferences depends very heavily on each person to decide what they like. This review is about why I upgraded from plossls to UWANs, why I like them, what makes them a joy to use, and what I discovered about using them that will hopefully be of help to others who are considering moving up to ultra wide angle eyepieces in at any point in their futures.

The UWANs from the top - 16mm, 7mm, 4mm


The 7mm UWAN

Wow – this was stunning – I was very impressed with everything about it from the moment I got it. I was surprised at how much larger and heavier the 7mm UWAN was over the 8mm TV plossl. I tried a number of things to see how it compared on all sorts of objects to the 8mm TV plossl I had. I tried it during daylight, and found it quite pleasing. I had read about a black out effect that occurs especially during the day with ultra wide field eyepieces, and found that I was easily able to position my eye to avoid not only the black out but to see nearly the entire field of view at one time. I was surprised at how much more comfortable it was to look through in the daytime than the plossls, due primarily to the larger glass element and extra eye relief. I didn’t feel like I had to peep through a tiny hole, and get my eyelashes touching the glass to see through it. 82 degrees is a wide area, and my eye really can’t grasp it all at once, but I found that I could get the rubber eye guard adjusted, and leave it alone, and I was pretty set with easy viewing, and could actually look all directions to take in the edges of the view as needed. I really had no problem with any black out effect during the day or night with this UWAN, or any of the UWANs for that matter. Note: I don’t wear glasses, and while I think the eye relief was much better than comparable plossls, it may be tight for someone who has to wear eyeglasses while viewing. I have no way to test this or confirm this so it’s just a general feeling.

I compared it to the other TV plossls I had, and took a few notes regarding what I saw while stargazing at night. I was surprised, that to my eyes, everything I viewed appeared as bright as the plossl. I was expecting to be able to see significant light loss due to extra elements, but I didn’t. I guess whatever light is lost due to the extra lens elements is not perceivable by my eyes. This is also likely a testament to the coatings which appear to be excellent to me. On the moon, I liked it better than the plossl, because it showed a much wider field of view, and seemed just as sharp to me. In fact, it was able to show the entire full moon easily, and allowed for much easier centering in the view, without any loss in contrast that I could see. I didn’t notice any false color on the moon, nor did I have any trouble keeping the entire moon in focus. I didn’t see reflections, or ghosting, and the detail I could see at about 79X was amazing. On open clusters it was hands down a better eyepiece, yielding equal magnification but a wider field of view, or better yet, equal field of view but at higher magnification. By my estimates, the 7mm UWAN provided 75% of the field of view as the 15mm TV plossl, but at twice the magnification, yielding fantastic views of open clusters that would fit in a little over 1 degree of sky. Stars stay sharp to the edge in my combination, as they were in the TV plossls, but it was just more fun to use. The difference between 50 degrees and 82 degrees is immediately noticeable, and quite amazing to the eye. The eye relief was much better than the 8mm plossl, and even the 11mm and about the same as the 15mm plossl, which made it very comfortable. When I compared it the 8mm plossl, it seemed to me that the contrast on open clusters was better, perhaps this is an illusion due to the wider field of view, and the contrast on globular clusters and planetary nebulas was about the same.

The only thing that I could really notice a difference on was Saturn and Jupiter, and on the very brightest of stars. The brightest stars and planets seemed to show a bit of scatter, sort of a light glow around the object, almost as if dew was just starting to settle on the objective (I checked, it wasn’t). These are not designed or marketed to be specialized planetary eyepieces, and everything I have read about the TV plossls seems to indicate that they are near the top of the pack for use as planetary eyepieces, so I sold the TV plossls. Huh? What did I say? – yes, I sold them. Why would I do that? Well the answer is simple. There are really only two planets that I find interesting, Jupiter and Saturn, and I rarely get great steady skies that warrant long looks at planets. I found that I was using the 8mm TV plossl the most, along with the Celestron Ultima 2X Barlow to view planets, and while this was crisp and high contrast, it was also uncomfortable to use, with its narrow 50 deg FOV, and tight eye relief, and was ending up at 7 elements of glass anyway. With the plossl, one slight bump of the scope, and the planet was out of the field of view. So off to Astromart they went, but before I sold them, I bought the 16mm UWAN, so I could compare it to the 15mm TV plossl side by side.

The 16mm UWAN

By now it was mid August, and that means I get maybe a two or three week window where I have a shot at seeing some of the wonders of Sagitarius and Scorpius, towards the center of our Galaxy. I have a large amount of light pollution to the East from the city of Chicago, and almost as much to the South from the glow of the Suburbs, so I tend to have the best luck with DSOs and my 80mm APO WO refractor straight up, or to the West and North. Nevertheless, I still search for objects to the South, as there are many objects that never get close enough to Zenith so I make the best of what I can find.

The first night I got to try the 16mm UWAN, I was completely amazed. It almost seemed impossible that this eyepiece was performing like it did on the first night. Perhaps it was the ultra wide field, or perhaps it was an exceptionally clear night, but I found myself seeing things I had never found or seen with the plossls. For whatever reason, I just had no problem finding things I normally struggled with like the Swan Nebula, or the Lagoon Nebula. This made no sense to me, so I switched back to the 15mm TV plossl, and strangely, I found that my eye and brain was simply better able to see with the 16mm UWAN. Faint deep space objects seemed to stand out better to my eyes. I can’t say that it was brighter, but it the contrast was equal on DSOs, and the extra field of view simply made nebulas easier to find. Globular clusters were also much easier to find, and I soon sold all of the plossls I had, including an Orion Highlight plossl that was 6.3mm with extremely short eye relief. I was amazed at how much easier it was to find the Hercules cluster, and others globular clusters with the 16mm UWAN – they just popped right out as I was scanning the sky for them. I found that it was fun to just pick an area of the sky and just slowly scan for things, often amazingly finding things and then going and trying to figure out what I found. Even double stars like Mizar seemed just as crisp to me as they did in the plossls. In fact everything I looked at seemed to be easier to see, more comfortable to view, and the eyepiece was just more “fun” to use.

But the 16mm UWAN isn’t perfect, I see a tiny bit of curvature to the field, and stars right out near the edge get soft. Perhaps it is not the eyepiece, but the field curvature that is inherent in the refractor that is the real culprit, but just the same, if I focus so that the center is in focus, the stars at the edge are a little soft. Conversely, if I focus on the stars at the very edge, the stars in the center are a little soft. How much of a focus shift is required? I haven’t tried to measure it in focuser travel, because it’s too small, but it’s about a half a turn of my small 10:1 two speed focuser knob, which isn’t very much, just enough for my eye to be able to get those edge stars sharp again. Well, considering that this eyepiece is showing over 2 degrees of sky, this is a very worthwhile tradeoff.

The 4mm UWAN

Summer turned to Fall, and Fall to Winter, and under the Christmas tree was a brand new 4mm UWAN. I had gotten very few observing opportunities in Fall due to clouds and rain, and other things that take precedence, like family, so I was eager to try the 4mm UWAN on Saturn, and the Orion Nebula. The first night out, on a very cold night in January, I was very pleased to find out that the 4mm UWAN worked extremely well on the Orion Nebula. On Saturn, or Sirius, it worked well, but displayed the same slight scatter as the others did on very bright objects. Again, this is not to say the eyepiece does not perform extremely well, it does; it’s just not designed to be a dedicated planetary eyepiece. The image is sharp all the way to the edge, and even the moon shows only slight false color when it gets to the very edge of the immersive 82 degree field of view, at about 139X and .6 degrees of sky. Back to Orion – WOW! – now this is really something. The view is amazingly good, better than I ever remember it at this magnification when I tried to Barlow the plossls. The four Trapezium stars are extremely sharp and clear but I couldn’t make out any hint of the 5th or 6th stars. I have to keep remembering I have an 80mm APO refractor – sharp, crisp, no false color, but still only 80mm of aperture. This eyepiece was just a joy to use at this power and field of view, and may be my favorite. I found I was able to keep things in its ½ degree field of view surprisingly easily. Again, this eyepiece, proved worthy of the same high marks as the other UWANs.

UWANs from the bottom 16mm, 7mm, 4mm


Calculations and indoor testing on the test charts

Using a handy spreadsheet I found on the Internet, call the Telescope Master, I was able to easily calculate what these eyepieces end up looking like in my scope, which is an 80mm WO Megrez 80FD, at a focal length of 555mm.

The 16mm UWAN provides a magnification of 35X and 2.4 degrees of real field of view, while the 7mm UWAN is 79X and 1 degree of sky and the 4mm UWAN is 139X and 0.6 degrees of sky. This makes for a very logical combination along with my 33mm SWAN which gives me 17X and 4.3 degrees of sky. All in all, this combination of 4 eyepieces gives me everything I need except for perhaps something around a 3mm eyepiece dedicated for high power planetary use on those few nights a year I get steady skies and can see Jupiter or Saturn.

I used two different test charts indoors to compare optical image quality in daylight. One chart is a grid pattern that allows me to check for field of view, edge sharpness, and distortions. In general all produced a flat field with the 16mm showing the small bit of field curvature toward the edge as previously mentioned. The 4mm and 7mm didn’t show any curvature that I could detect, and in all three there was a very slight barrel distortion seen, but not enough to be visible on anything but my grid chart. Using a high resolution test chart, I was able to determine that there are no other optical distortions that I can see. All-in-all, these are exceptional in optical quality for the money as far as I can tell, when used as tested in my WO 80mm APO refractor.

Conclusions: What makes the UWANs so good?

Let’s move in from the outside starting with the box. The packaging is high quality, like all WO products I have ever purchased. The box they come in is well made, well protected in foam, and in a plastic bag with silica gel for safe shipping. The caps, both ends, are well made, much softer and better fitting than the ones that were on my other eyepieces, and have a nifty WO logo on them, unlike the hard plastic ones found on some other eyepieces. They stay surprisingly soft even in below freezing weather, and all fit snuggly, so there is no chance of them falling off while picking up the eyepieces in the dark. By the way, even in sub freezing temps, I didn’t have any problems with these eyepieces at night, and they went from 70 degrees Fahrenheit in my house out to 15 degrees a couple of times.

Now let’s look at the eyepiece itself from the outside in. The eyepieces are nice looking, all black, with black knurled rubber to grip, and a black twist up soft rubber eye guard. This twist up eye guard feature is really nice, because it allows you to set it where you like, and then leave it there. It turns easily, both up and down, but stays were you leave it, and makes for a very comfortable eye placement aid. Next we have the insertion tube, the end that goes into the diagonal, the part that gets tightened down on. WO chose to use a tapered safety cut, and this alone may be worth the price of admission, to me. It wasn’t until I used the standard undercut eyepieces a while that I realized what others were saying. The darn undercut, seemed to catch on the compression tube that tightens to it, nearly every time I was switching eyepieces. Darn it, if that didn’t cause me to bump my EZTouch mount enough to throw it off sometimes when I was changing eyepieces while I was using the plossls. With the WO tapered barrel, this doesn’t catch on the ring that tightens it in place, and like magic, I was finding that I wasn’t accidentally moving the scope while changing eyepieces any more! This may sound trivial, but it is a seriously NICE feature that I wouldn’t have seen any advantage until I had used these for a while. The entire eyepiece itself has a very solid look and feel, and really feels substantial in your hand. There is nothing cheap or skimpy about the UWANs, and all components seem to be well made machined parts, that fit together flawlessly.

Now let’s move to the rest of the eyepieces’ components. The coatings appear excellent, without any noticeable flaws or issues. Shining a strong flashlight into each and taking flash photos reveals to me that the coatings are doing a great job of eliminating reflections. Each eyepiece is different enough in size, which is good at night, so that they are easy to tell apart in the dark just by the feel of them in my hand. Unscrewing the barrel, reveals that each eyepiece has a rather large field stop, placed between the barrel glass elements and the rest of the eyepiece. Everything inside the eyepiece I looked at appeared to be flat black, with no visible reflections or shiny surfaces, and well assembled. I didn’t see any flaws, either optically or mechanically on any of the eyepieces. The three I have are parfocal, meaning that they can be interchanged without major refocusing. I find I slightly refocus each, as there is a very slight difference in focus point but they are very close and don’t require anything but a touch to make sure that focus is dead on. All three have approximately the same eye relief, and the adjustable eye guards can all be left in the position that I found to be the most comfortable and simply exchanged as needed in my scope very easily and quickly which makes for a very enjoyable viewing experience.

What are they Best Used For?

Well this is totally my opinion, but I think the UWANs are really best for what I like to view, and what I am best able to view with my 80mm APO Refractor, from the light polluted suburbs of a big city. This includes stars, double stars, open clusters, globular clusters, and planetary nebulas, all from the non-tracking alt-az EZtouch mount. Diffuse nebulas are tough for me, as are galaxies, so when I get a scope some day with more aperture, these eyepieces should prove equally valuable. The moon is a great target with these eyepieces, and planets, while not their specialty are actually pretty good. It’s obvious to me that with my light pollution, I simply enjoy the views more with higher magnification, and wider field of view eyepieces like these UWANs.

Other factors to consider about the UWANs

They are still more expensive than the various budget widefield eyepieces out there, or even the best plossls, since the 16mm is priced at $238, and the 4mm and 7mm at $198. While cheaper than many other premium eyepieces, the price is always a consideration for me, so I bought them one at a time, as I could afford them. The sizing choices are limited to the 4mm, 7mm, and 16mm in 1.25” barrels, however WO also makes a 2” 28mm model, that I have so far successfully resisted the temptation to buy. I’m not sure how much longer I can resist, but at $398, it is not a spur of the moment buying decision for me. Eye relief might be tight for someone with glasses, but for me was very comfortable. They are each described as having 7 elements in 4 groups, which combined with an 82 deg FOV. Some may like this design, some may not, and there might be better choices for someone looking for a dedicated planetary eyepiece, but for the overwhelming majority of my viewing, the UWANs have been a great investment for me.

Click here for more about this subject. -Ed.

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