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William Optics UWAN Eyepieces

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The William Optics UWAN Series
by Dr. Carsten Reese

Fig. 1: The William Optic UWAN series

About myself

Before starting with the review itself I would like to tell you about my background on eyepieces. I am a German reseller for astronomical accessories, and very specialized on eyepieces. Some reviews I wrote about eyepieces and filters have been published in the "Interstellarum", a German astronomical magazine. For CloudyNights this is my first review. If you like it - give me a feedback, if not - try to give me hints for doing better next time.

The UWAN series

The manufacturers of ultra wide angle eyepieces have got a new competitor - William Optics with its 82-deg UWAN eyepieces. At this time the focal length 4, 7, 16 and 28mm are available. I got the series directly from William Optics for evaluation purposes. Some reviews have been written meanwhile, e.g. by Tom Trusock on CloudyNights (04/06, http://www.cloudynights.com/documents/uwans.pdf). Tom compared to the Nagler series, so this review will not repeat that, but take some other brands for comparison, namely the 82-deg Meade 5000 UWA, the 70-deg Pentax XW and the 68-deg Baader Hyperion eyepieces.

But, let's start with a description of the UWAN series.

First impression is - black. Different to other eyepieces the 1 1ž4" or 2" barrels are black anodized, not chromed. Instead of a simple recess the barrels partly have a conic shape to keep the eyepiece safely in the focuser, even when using a compression ring. The overall design is close to the Nagler's: functional, robust, very well manufactured - with some exceptions. The ring surrounding the eye lens showed some variance in the color. Seemed not to be by accident, as 3 out of four eyepieces were not perfect here. Another issue were two minor flaws on the field lens of the 16mm UWAN. Right at the edge two small areas were visible, where obviously something has gone wrong (see Fig. 2 for these topics). As the amount was small, and this was just the edge behind the fixation ring, the optical performance should not be effected.

I contacted William Optics for clarification. The color variation in the ring is due to the lubricant exude from the twist-up eyecup on the aluminum ring. If you moisten your finger, you can rub it off. However, I would expect to get a cleaned eyepiece and I do not like to rub near the eyepieces lens. Also the second issue, as the first one, was not taken very serious. It should probably be caused by the anodized retaining ring which projects on the corner of the lens. So I tried to find the answer by my own and put it under a binocular microscope, where I found that there are some gluing and color remnants on the lens.

So, in total a small minus concerning quality control remains.

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Fig. 2: "Nitpicking" - Some quality issues.

A really nice feature is the twist-up eyecup. Much better than the Meade adjustment, which is not perfect at all, and simpler, but not worse than the Pentax solution. However, the eye relief of the eyepieces is not as generous that you will have to use it completely twisted up. The eye relief of all focal length is comfortable (28mm) or even sufficient (4, 7, 16mm) for those who do not wear eye glasses. If you have to - look for other eyepieces.


Barrel Size


Weight 2)


Eye Relief1)

Field Stop Dia. 2)

Price US-$

UWAN 28mm








UWAN 16mm

1 1ž4"







UWAN 7mm

1 1ž4"







UWAN 4mm

1 1ž4"







1) Manufacturer Data
2) Measured Values
Table 1: Specifications of the UWAN series

4mm UWAN vs. 3.5mm Baader Hyperion

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Fig. 3: UWAN 4mm (left) and Baader Hyperion 3.5mm

Laboratory investigations

I have established a personal standard test setup for eyepieces. A telephoto lens (Vivitar 135mm) is used as a small telescope, knowing that this lens is well corrected to have a flat field and low distortions in the focal plane. So this setup is close to a "slow" telescope. Using an USAF resolution target as well as color- and square targets allows to get information about sharpness, contrast and distortion as well as true field of view. Do not take this as scientific measurements, but it helps a lot to judge some aspects of eyepiece performance.

Concerning sharpness the UWAN is perfect in this test. In this case (low focal length eyepieces) the resolution limit is given by the diffraction limit of the telephoto lens, and the UWAN reaches this limit over the whole field of view. For the Hyperion, starting from about 70% of the field sharpness is going down to the edges, but still remains good.

The UWAN shows noticeable pincushion distortion, the Hyperion is almost free of distortion. A word on distortion should be added here: You will not take notice of distortion in astronomical observation unless viewing the moon or planets near to the edge. However, the true field of view is affected, which will be less if pincushion distortion is present. Concerning contrast there is a clear vote for the UWAN, the Hyperion is not as good, but the shorter focal length causes at least a part of this difference. Both eyepieces are slightly warm in tone. The true field of view of the Hyperion is 77% when the UWAN is set to 100%. Take the manufacturer data of the different apparent field of view and focal length into account, and one will see that there is a difference of a couple of percent, which is due to the distortion of the UWAN.

At the 8 inch, F/5 Newton

For all eyepieces different well known deep-sky objects have been used to determine resolution aspects (M13, e1/2 Lyrae), ghosting and light scatter (Vega), edge performance (Alcaid), and contrast (again M13, M57, M27, Cirrus-nebula with O[III]-filter). The latter were used also just to enjoy and to become familiar with handling and viewing.

The Baader Hyperion series is known to have a good price-performance ratio. I definitely agree with this rating. It's a 68-deg Super Wide Angle series with comfortable 20mm eye relief, the optical design very close to the well-known Vixen LVW series. However, the 4mm UWAN outperformed the Baader Hyperion clearly. The UWAN showed about 95% of the field more or less without deformation on stars, very close to the edge some color appeared (blue inside). The Baader has about 90% of its smaller field of very good performance, also color at the edge. Looking at Vega and, second, placing it a little bit out of the field of view, lead to two beams of reflections in the Baader, whereas the UWAN was perfectly dark here. The amount of scattered light was somewhat higher for the Baader. Even contrast was better with the UWAN. You have to take into account that the focal length is a little bit shorter for the Baader, and the higher magnification will lead to some loss in contrast, but this seems not to be the whole story here.

Eye relief was acceptable for the UWAN, and very comfortable for the Baader.

7mm UWAN vs. 6.7mm Meade UWA Series 5000 vs. 7mm Pentax XW

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Fig. 4: The Meade UWA 6.7mm (left ), Pentax XW 7mm (centre), and the UWAN 7mm

Laboratory investigations

During the laboratory investigations it turned out that the measurement results did not fit with the 7mm focal length as stated by William Optics. First, when determining the resolution the UWAN showed 10 to 20% less absolute resolution than the Meade and the Pentax. However, the sharpness looked really identical, on axis a perfectly sharp image obviously limited by the eye's resolution ability only. Second, the true field of view was found to be about 20% bigger than for the Meade, whereas distortion was similar. The only conclusion to put a sense in this is that the focal length of this eyepiece is not 7, but close to 8mm. Big surprise, as to my knowledge nobody has noticed this yet.

The sharpness measurements showed a perfect Pentax, resolution limit was just the eye's ability to resolve not better than approx. 1 arc minute within the apparent field of view. This is valid over the whole field of view. The Meade as well as the UWAN (now supposed to have 8mm of focal length) are identical over most of the field, but close to the edges resolution is going down a little bit.

Distortions where present in the Meade as well as in the UWAN, where a noticeable amount of pincushion appears. The Pentax is almost free of distortion. The contrast is slightly better with the Pentax (really excellent), but very good also for the Meade as well as for the UWAN. The UWAN is a little bit warm in tone, whereas Pentax and Meade give a purely white impression - up to you what you prefer.
The true field of view, when setting the UWAN to 100%, is 78% for the Pentax and 82% for the Meade. Distortion is playing a role in this, but the a.m. difference in focal length is doing the major job here for the UWAN.

At the 8 inch, F/5 Newton

I spent a lot of time in comparing these eyepieces at the telescope, but it was really hard to come to a conclusion about differences concerning contrast, edge performance, ghosting, and light scatter. All three do a really fine job here. The difference in contrast as seen in the laboratory could not be found at the telescope, they are head to head. Edge performance was very similar for all eyepieces, deformation of stars was only visible in the outer range of the field, and the amount was low. Keep in mind that the Pentax just offers 70-deg apparent field! Vega was used to look for ghosting and light scatter. As a result the coatings seem to be superior in all cases - no ghosting, low amount of scattered light.

At the e1/2 Lyrae, where the Meade as well as the Pentax clearly showed a dark zone between the double-doubles, the UWAN just accidentally offered this view. This is again not due to a lack of sharpness, but of lower absolute resolution caused by the longer focal length. Eye relief was a little bit more comfortable with the Meade compared to the UWAN, but nothing really to be taken into account for a decision. The Pentax with its generous 20mm eye relief is unbeatable in comfort here, but the apparent field of view is significantly smaller than for the other two eyepieces.

16mm UWAN vs. 14mm Meade UWA Series 5000 vs. 14mm Pentax XW

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Fig. 5: Meade UWA 14mm (left), UWAN 16mm (centre), and Pentax XW 14mm

Laboratory investigations

Within the sharpness measurements the Pentax showed some resolution degradation starting at about 70% of the field. The UWAN performed better, just for the last 10% of the field the resolution wasn't as perfect as in the centre. Sharpness of the Meade was very good at the centre, but from about 70% to the edge noticeable field curvature leads to loss of resolution. Distortions are similar to the other focal length - noticeable pincushion distortion for the UWAN and the Meade, "orthoscopic" view through the Pentax. All three eyepieces do have an excellent contrast and give an image without noticeable coloring.

The true field of view, again setting the UWAN to 100%, is 91% for the Meade and 83% for the Pentax. The difference to the Meade is more or less just caused by the difference in focal length. Comparing it to the Pentax and correcting for the different focal length and apparent field of views leads to the conclusion that the true field of view is about 10% less for the UWAN as it would be without any distortion.

At the 8 inch, F/5 Newton

All three eyepieces did not perform very well at the F/5 Newton. The Meade suffers from a clearly noticeable field curvature, as already seen in the laboratory. Starting at about 50% of the field stars become blown up and clearly defocused at the edge. The UWAN showed a better image, but also far from perfection. Beginning at about 60% of the field stars are deformed. A combination of astigmatism and a slight field curvature makes it the least eyepiece out of the UWAN series. Also the Pentax is not without problems, it offers about 70% of the field of view a very good image quality, but towards the edges mainly coma appears. Views with these eyepieces are not really bad, especially when only faint stars are within the field these edge problems are not prominent, but things could be better.

Concerning contrast, ghosting and light scatter all three eyepieces are very good. No reflections could be detected, and Vega was surrounded just by a weak and small area of scattered light. Impossible to decide which eyepiece performs best.

Eye relief was similar to the 7mm comparison, with some more difference between the UWAN and the Meade. So the UWAN has an acceptable eye relief, the Meade is comfortable, and the Pentax generous.

28mm UWAN vs. 30mm Meade UWA Series 5000

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Fig. 6: UWAN 28mm (left) and Meade UWA 30mm

Laboratory investigations

Sorry, there are no investigations in the laboratory - these huge eyepieces do not fit into the test setup.

At the 8 inch, F/5 Newton

Both eyepieces are not perfect to the edges, but give impressive views with huge fields of view. 80% of the field are excellent, on the last 20% some star deformation becomes visible. Due to the longer focal length of the Meade the true field of view is about 5% more than for the UWAN. Eye relief is comfortable for the UWAN, the Meade's eye relief is somewhat longer. No ghosting or reflections are visible, and again the amount of scattered light is low. Hard to say which one to prefer - a look on the price may help here.

As 28 or 30mm focal length combined with 82-deg of field on a F/5 telescope are a demanding task for optical designers, it can be stated that they have done their job very well. Just look and enjoy!


In total a really fine eyepiece series, well worth its money. Black is beautiful, take away the question mark. I personally would like a bit more eye relief, but this is the same issue than on the Naglers. The optical performance is very good, partly excellent. Just the 16mm eyepiece is somewhat behind in performance at F/5. Especially for the edge performance with a fast telescope the series is very clearly distinguished from cheaper eyepieces with 80-deg apparent field of view or more. I took the F/5 results as well as my experience with cheap Super- or Ultra-Wide-Angle eyepieces for this statement. However, I do not know how the Speers-Waler eyepieces perform.

In fact these eyepieces are playing in the same league than other premium eyepieces with some plus and minus in different aspects, and one of the advantages is simply the price. My personal rating on optics (without an eye on prices), in comparison with the Meade UWA series 5000 is as follows:

UWAN 4mm: Rating 9 1ž2 out of 10
UWAN 7mm: 9, Meade UWA 6.7mm: 9 1ž2
UWAN 16mm: 7, Meade UWA 14mm: 6
UWAN 28mm: 8 1ž2, Meade UWA 30mm: 8 1ž2

Comparison to Pentax or Baader Hyperion on a rating scale does not make a real sense here, as the apparent field of view is significantly less for these eyepieces.

So what is missing? I have made a comparison in an 8" F/5 Newton only, and in the laboratory. Things might look different a bit on other scopes. Room is left for more reviewsÉ

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