Televue have spent years crafting quality astronomical equipment to ensure they remain the kings of eyepiece construction. The Nagler series is amongst their finer offerings and while they cannot be considered cheap (at just shy of £200) the unwavering enthusiasm and skill that Televue bring to each eyepiece makes them well worth the money.
Televue have used a total of 7 lenses arranged into 4 groups in the Nagler's construction. It's usually preferable to minimise the amount of glass between the object being observed and the observer. To get around the potential image degradation that can be introduced with an abundance of elements, Televue have incorporated a high quality, low dispersion glass with full multi coatings to improve light transmission. Therefore the extra lenses are an asset rather than a burden to this eyepiece making it possible to achieve a mighty 82 degree field of view which is ideal for a predominantly Lunar/planetary eyepiece. The huge field means objects stay in view for longer without the need to readjust the telescope.
Optically the 5mm Nagler performs incredibly well, up to the usual high standards set by Televue themselves. When discussing wide field eyepieces one of the biggest complaints is image degradation in the outer portions of the field, the 5mm remains unbelievably crisp and sharp right the way to the edges. Stars are point like dots even in the outer 5% with no sign of seagull shaped distortions to be seen.
Colour rendition is important on any high powered eyepiece but the Nagler's feels much warmer and fuller than most. Observing the subtle differences within Jupiter's atmosphere in shade and tone is a very satisfying experience with this Televue.
Contrast is high, particularly noticeable when observing shadowy craters on the Lunar surface. This is also where the massive 82 degree field comes into it's own. Viewing so much of the Moon at such high magnification is an awe inspiring sight.
The Nagler's high quality optics are complimented well by an extremely comfortable design. Eye relief is very generous for this focal length at 12mm. Eye relief is the maximum distance you can move your head from the objective lens whilst still taking in the whole field of view). 12mm is enough to make the Nagler suitable for eye glass wearers. As well as a nice eye relief the 5mm has a decently sized objective lens.
In conclusion, the Nagler is an outstanding wide field eyepiece that suffers from none of the afflictions associated with its analogues. It's not only produces stunning views but is a joy to look through with a refreshingly long eye relief and large objective diameter.