The Swan, an elegant and majestic creature and also the acronym that describes this 15mm offering from William Optics. Standing for Super Wide Angle this eye piece is just that, using 5 optical lenses in 4 groups WO have managed to wrench a magnificent 72 degree field out of this SWAN, (quite a neat feat for an eyepiece with so relatively few elements).
Originally starting out with the production of quality refractors William Optics have proved they are not only competent in eyepiece manufacture but actually excel at it, devoting as much time and attention to their lens craft as they do to their widely successful telescopes.
The secret of the SWAN's success lies in its outstanding performance married up with it's utter affordability, there aren't many wide field eyepieces out there that can be snapped up for such a miniscule price tag. You'll only be parted from £70, with each penny of that being invested in an eyepiece that, simply put, will not let you down.
From a budget wide field eyepiece you would be forgiven for expecting a certain degree of image degradation toward the outer field and while there is a slight amount present in the outer 5-10% of the field, it isn't significant enough to be considered a downside. In fact it is quite the reverse, WO have done fantastically well to keep image quality so consistently high over 90% of the field. Colour rendition is superb also, providing some of the warmest views of Saturn's tiny disk I've had, effortlessly showing the subtle nuances of it's golden atmosphere.
But at 15mm this ep will get most of its use on deep sky objects, outside the Solar system. To this end, one of the most important factors that any deep space eyepiece can have is contrast. Dissecting the eyepiece reveals internal baffling which is a good sign (internal baffling refers to the use of dull matte paint in coating the inside of the ep, this helps keep light from bouncing around inside the eyepiece and therefore yields more crisp and contrasty views).
Thankfully WO have blackened the very edges of the SWAN's lenses as well, a simple step sometimes overlooked that can have profoundly positive effects on performance.
The optical surfaces of the SWAN have been fully multi coated. Some eyepieces are just fully coated whereby all lenses are covered in a single anti-reflective layers. Other eyepieces are multi coated where only the lenses exposed to the air are covered in multiple layers while the rest receive a single coating. Fully multi coated eyepieces receive multiple layers of anti-reflective coating on every single lens, drastically improving light transmission.
Optically the SWAN is a magnificent eyepiece (and would still be with a price tag many times higher) but if an eyepiece is unpleasant to look through then it's game over, all the pristine views in the entire universe cannot compensate for a head ache inducing eyepiece. It gives me enormous pleasure then to announce that the SWAN is perfectly comfortable to use! It has a decently sized objective lens which means no need to contract eye strain and the eye relief is 14mm. While this cannot be considered overly generous it is long enough so as never to become a problem and also makes this ep more than suitable for eyeglass wearers.
To conclude the SWAN is as beautiful a thing as its namesake. It's very rare indeed to be able to experience such wide field views at such a low cost. The care and attention William Optics lavish on their eyepieces is clearly evident and manifests itself in an altogether higher caliber of lens.