Since the Nagler type eyepiece was first created by Al Nagler of Televue over a decade ago it has undergone constant evolution in an attempt to reach eyepiece perfection. The 13mm is amongst the sixth wave of Naglers to be released and represents the pinnacle of excellence for Al and his name sake optical system.
The 13mm uses 7 elements in it's construction spaced into 4 groups. In the budget category of eyepiece introducing extra lenses to an eyepiece can sometimes serve to degrade image quality but Televue have used a high quality glass as well as an excellent lens coating that improves light transmission to counter the potentially negative effects of additional elements. With 7 lenses, Televue have managed to get a staggering 82 degree field of view out of the Nagler.
At 13mm this can be considered an interim eyepiece where power is concerned, offering enough magnification for serious observation of the Moon and planets while still being effective for deep space observations. An 82 degree field of view and a 13mm focal length will be more effective on deep space objects than a higher focal length with a smaller field (especially in light polluted suburbs). Higher magnifications have the effect of dimming the night sky making faint objects stand out easier against light pollution.
Optically the 13mm has a beautifully flat field and image quality holds strong throughout 100% of the field. Stars are defined as points right to the edges and contrast is exceptionally high. Colour rendition is superb, the 13mm offers some of the warmest views I've experienced through an eyepiece. There is no light scatter or any other type of aberration to keep this Nagler from perfection.
As you may expect with such dedication to the astronomer as Televue exhibits the 13mm is a joy to look through not only optically but from a comfort perspective. 12mm of eye relief means you won't feel restricted to keep your head squared stiffly against the objective lens and 12mm makes the 13mm suitable for eye glass wearers. A nice sized objective lens adds to the observers comfort and means you won't give yourself eyestrain whilst lingering over the flawless views you'll receive through this Nagler.
At just over £200 there are cheaper offerings out there but if you can afford the initial cost you will save in the long term as there will be little need to buy another similarly focal lenghted eyepiece again. Highly recommended for it's wide, flat, quality views and comfortable set up.