William optics are a superb manufacturer of astronomical equipment amongst which are the fantastic SPL range (standing for Super Planetary Long eye relief). Within the SPL range are the 3mm, the 6mm and the 12.5mm. Whilst the 3mm and 6mm offer very high power views the 12.5mm offers a more realistic magnification that ensures it will get used more often than it’s higher powered cousins.
Once you get over a certain power threshhold (dependant on the telescope you own) you are at the mercies of the Earth’s own atmosphere. For the most part the 3 & 6mm SPLs will only get used on the rarest of occcasions and that’s what makes the 12.5mm the best choice for consistant observation.
William Optics have used 7 elements (lenses) grouped into 4 in the SPL’s design. Usually the addition of extra glass to an optical system can only serve to degrade image quality, however in the case of the SPL the glass is of an excellent quality and WO’s supreme full multi coatings mean each lens performs as well as it possibly can. In fact the extra lenses don’t degrade the image at all and give the SPL a very comfortable eye relief. Eye relief is the distance one can hold ones head away from the optical lens whilst still being able to see the whole field of view. Coupled with a large objective lense (the one you gaze into) the SPL is effortless to look through.It doesn’t produce eye strain or headaches that can occur in certain eyepieces with low eye relief and small objective diameters.
It must be said that all the extra elements have made the SPL a little heavier than your average eyepiece which can produce balancing issues when swapping between the SPL and lighter eyepieces.
Optically the 12.5mm is very pleasing. Contrasted and colourful views remain tack sharp right out to the edge of the 55 degree field of view. There is no spurious colour and no seagull shaped stars even in the outer 5% of the field.
When you consider the 12.5mm costs just under £70 it really is incredible how William Optics have achieved such a high level of quality. An eyepiece that is not only optically superb but very comfortable to look through, they even manage to look aesthetically pleasing to. A definite recommendation as a lunar/planetary eyepiece of exceptional quality.
