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Celestron Omni 12mm Eyepiece
by Revier
Celestron's basic Plossl comes in the shape of the Omni. It uses 4 lenses (or elements as they're sometimes known) in a symmetrical layout, that is to say two groups of two lenses spaced closely together. This is a classic Plossl design that has pluses and weaknesses.
On the plus side the use of only 4 elements makes images ... crisp and clear whilst keeping the price of the eyepiece down. On the down side this configuration of lenses yields only a 52 degree field of view. The 52 degree field would matter more on a higher focal length but at 12mm objects are small enough to be held within the field longer than a few moments.
As this is a medium powered eyepiece it will get used not only on the moon/planets but also on deep sky objects such as nebula and galaxies. The small field of view and the magnification will make it useful on all but the largest objects (such as the veil and M31). As this will be used on very faint and elusive objects outside the solar system, contrast is very important. The blackened edges of the lens elements help wring every bit of contrast out of this Plossl.
As well as contrast a good eyepiece should transmit as much light into the observers eye as possible. Celestron have used their renowned lens coatings to keep images bright, especially important for detecting galaxies.
Optically the Omni performs well, there is no significant light scatter and objects stay sharp throughout the entire field. Where the Omni really excels is contrast, especially apparent when observing the Lunar surface. Craters are dark in shadow and the various ejecta found near recent (astronomically speaking) impact sites is bright and defined. Colour rendition is okay but not great providing a somewhat colder view than other eyepieces. Saturn in particular looks almost drab due to the lack of strong colour in this eyepiece.
Visually the Omni is a mixed bag, while images are crisp and contrasty accross the whole field the lack of colouring has a profound effect on viewing pleasure, making the planets and moon seem almost sterile.
Comfort wise the Omni has a rather disappointing eye relief of 8mm (eye relief being the maximum distance you can position your head away from the objective lens). This makes viewing quite uncomfortable and I doubt whether this eyepiece would be enormously useful to anyone wearing glasses.
Strong points of the Omni include crisp, sharp and well contrasted images and a reasonable objective lens size while poor points include lack of colour rendition, a short eye relief and a lack of a rubber grip ring to help prevent dropping when fingers are cold and numb. There are better eyepieces out there in the £40 price band but it isn't completely useless.
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Tele Vue Ethos 3.7mm Eyepiece
by Revier
Al Nagler is at it again with his endless pursuit of perfection in the wide field arena. The new 3.7mm Ethos is out and due to limited supplies I may be one of the first people to have looked through it.
First off this is a mighty eyepiece physically and it does weigh quite a lot at just over 500 grams. It can be used in 1.25 ... inch barrels but also comes with an adapter that easily fits onto the eyepiece to enable it to be used in 2 inch barrels.
There is a rubber grip ring that comes in handy when fumbling with freezing cold fingers and a comfortable fold up flexible rubber eyecup (as opposed to the much less comfortable hard plastic eyeshields present on some eyepieces.)
Where the Ethos really shifts up a gear over it's rivals is in it's immense 110 degree field of view! By far the widest field eyepiece available, therefore one could be forgiven for assuming it would suffer from the same issues that plague other wide fielders such as image degradation in the outer field.
That's where you'd be wrong. It is unlike any eyepiece I have ever used in that it doesn't suffer from any abberations accross any of it's massive field.
Objects were so sharp and crisp, full of contrast. The many subtle shades in Jupiter's atmosphere were picked out exceptionally well, I've never hade a view of Jupiter like it.
On the moon words cannot do justice to it's performance. Such a gargantuan field of view at such high magnification is something that needs to be experienced to be believed. Craters showed amazing definition and you actually find yourself having to physically move your head around to take in different portions of the view at any time.
Amazingly for such a high magnification Televue have got a very comfortable eye relief out of the 3.7mm, around 15mm making it a pleasure to look through and suitable for spectacle wearers.
It must be said that at such a low focal length this Ethos will only get used on the steadiest of nights but even the chance to use it a few times a year would be worth it's £500 price tag.
For those who have been anticipating the 3.7mm for sometime, it lives up to every bit of the hype. For those who have never looked through an Ethos you will be in for an absolute treat.
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Televue Nagler 5mm 1.25" Eyepiece
by Revier
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.
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