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Celestron X-Cel 5mm Eyepiece
by Revier
The Celestron X-Cel 5mm is a high powered eyepiece for planetary and Lunar viewing. The 5mm focal length makes for a high magnification whether your using a fast, slow, long or short telescope. Unlike the majority of eyepieces out there Celestron have used 6 lenses (or elements as they're known) in the X-Cel's manufacture.
... Most eyepieces use 4 or a maximum of 5 lenses as generally the fewer elements there are in an optical system the clearer and sharper the image will be. The extra elements have not been introduced to increase field of view (as may be expected), the field is only 55 degrees. The reason for the added glass is to increase the objective aperture, to put another way the lens you look through.
At shorter focal lengths (such as 5mm) some eyepieces can feel like you're looking through a pin prick, this can cause headaches and eye strain and is clearly undesirable. The X-Cel doesn't suffer from this problem and is very comfortable to look through. It also features a very generous 20mm of eye relief. Eye relief being the distance one must position ones head away from the lens to see the whole image. Due to the eye relief this eyepiece is suitable for people who wear glasses.
Optically the X-Cel performs well for it's price range (£60). Special low dispersion glass has been used on the most curved lenses to minimise light scatter and other abberations. Each lens element has been fully multi coated to improve light transmission.
If you buy more than one eyepiece from the X-Cel line you will be pleased to hear they are all par focal. That is to say that once you have achieved focus with one you won't need to adjust focus when swapping for another X-Cel eyepiece.
The body of the eyepiece feels strong and durable and features a rugged rubber grip ring to help avoid any accidents (especially common when observing in the freezing cold with un-gloved hands). Another handy feature is that the silver metal barrel has a safety groove cut into it, this stops the eyepiece falling out of the telescope if not properly secured.
The X-Cel is heavier than an equivalently focal lengthed plossl (due to it's extra lens elements) but this shouldn't be enough for any significant balancing issues. Cosmetically this is quite a stylish eyepiece, long and slender with a white, orange and black colour scheme.
Recommended especially for the older observer whos eyesight may not be once what it was. Having said that younger observers can still benefit from the comfort this eyepiece offers. Optically the X-cel is above average, good contrast and a sharpness across 90% of the field means undriven telescopes will be able to let the planet drift through almost the entire field of view before having to reposition the scope to keep the object crisp.
To conclude as optically proficient as the X-cel is, there's no doubt its major selling point is it's oversized objective and generous eye relief. I would give it a 3 out of 5 for it's flat field and decent colour rendition (especially important on a planetary eyepiece) as well as it's mininmal light scatter, but I would give it a 5 out of 5 for comfort, a large and soft rubber eyecup compliments the long eye relief and the benefit of the large objective element should not be under estimated. Earning the X-cel a very respectable 4 out of 5 overall.
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Celestron 1.25" Star Diagonal
by Revier
Celestron are known for their high quality refractors at a reasonable price and if observing through such a refractor there is one piece of kit you won't be able to do without, and that is a simple star diagonal.
When observing through a refractor, the bussiness end (where you place your eye) is usually situated on the lowest ... part of the telescope off the ground (unlike most reflectors where observing is done at the highest point of the telescope).
If trying to observe without a diagonal you will quite often find yourself twisted and contorted into incredibly odd and uncomfortable postures.
The star diagonal's role is to provide a 90 degree angle to the telescopes light path meaning you can observe even the highest objects in the sky far more practically and comfortably.
The diagonal is inserted into the drawtube of your scope via a metal cylinder, a selected eyepiece is then inserted into the solid black plastic tube jutting out from the oppsite side and is easily secured with two silver thumb screws.
In the triangular body of the star diagonal lies two high quality polished mirrors that reflect light up into the observers waiting eye. During the process of this light reflection somehow the image becomes flipped around, North and South remain correctly aligned but East and West become reversed.
For most astronomers this topsy turvy orientation doesn't present a problem, once you're aware of it. There is a similar device available known as an erecting prism, this keeps images correctly positioned but at the cost of reduced optical quality.
Considering that this is one of the cheapest star diagonals available
(a little under £30) it performs fantastically. Foolishly I've allowed mine to get dusty and scratched, there really is no excuse for this though as Celestron include a solid black plastic cap as well as a see through thinner plastic cap to keep this exact thing from happening.
If you take good care of it this is the finest sub £50 star diagonal available. It doesn't noticeably degrade image quality (as introducing any extra glass to an optical system can potentially do) and the design is solid yet light enough not to cause balancing issues (say when removing the diagonal to insert a CCD camera).
Highly recommended, there really is no need to shell out over £100 for a decent star diagonal that gets the job done.
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Celestron Omni XLT 150
by Revier
Celestron are a company that excell in optical quality, due in part to their superior starbright XLT lens coatings that cover all their hand figured lenses. The coatings drastically improve light transmission meaning that even the faintest objects are as bright as possible through the scope.
As with the large majority of ... their other telescopes the 6inch reflector performs very well, the thin spider vanes supporting the secondary limit diffraction spikes, optically this reflector is a real treat.
It performs excellently on the moon as well as the planets and if taken to a relatively dark site it can handle deep space excellently. Transporting the scope is easy as the ota is only 26 and a half inches (measured).
Due to it's fantastic contrasty images and excellent light transmission the 150mm can easily pluck out faint details from a wispy and elusive galaxy or the subtle nuances of fine filaments within an emission nebula.
The tube is very light and as such it is more than accomodated by the CG-4 mount and tripod it is sold with. The CG-4 is a mount that gets a lot of use from me as it's low cost but excellently constructed. With oversized slow motion control knobs in right ascension and declination that make it really simple to track objects through the night sky (providing reasonable polar alignment has been performed first). Although the mount is made from solid metal it still is light enough to transport easily.
The finderscope that is sold with the scope is adequate for solar system work (it's a standard Celestron 6x30). The 6 pertains to the magnification whilst the 30 correlates to the amount of light the finderscope gathers when compared to the human eye.
For deep space work it may be necessary to upgrade to a 9x50 finderscope to help track down those ethereal fuzzies.
With a focal length of 750mm and superior 6inch optics the omni XLT 150 is excellently suited for deep space photography although for best possible results an upgrade to a sturdier mount maybe required (such as a CG-5 or EQ-6). The CG-4 is excellent visually for the price but won't provide the ridiculously high level of accuracy required for steady shots.
There is know doubt that visually the XLT 150 takes alot of beating especially when you consider it's £350 price tag. Photographing the solar system will be instantly within your reach without the need to upgrade the mount (although as the scope is only F5 you will need a high magnification Barlow to get a decent image scale, a x5 would be ideal).
With an upgrade in mount, deep space is waiting to be captured by the top quality optics of the 150. An absolute recommendation for it's optical quality, low cost and versatility.
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