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Celestron Omni XLT 102

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£415.79 Best Offer by: amazon.co.uk marketplace See more offers
1 Review

Brand: Celestron / Type: Refracting telescope

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      16.03.2011 18:41
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      Even with the inexcusable focuser the 102 scores highly

      Having owned the 102's bigger brother (the 120) for the last 5 years, I had to test out my Astronomy club's latest addition to its fleet of affordable refractors to see how it stacked up. It turns out the 102 performs very well indeed. The focal length of the 102 is 1000mm while its focal ratio is f9.8. The higher the f number the more suited the scope to Lunar/Planetary observations as the field of view is smaller and views are more magnified and dimmer. At f9.8 it becomes rather difficult to observe anything but the brightest and smallest of deep space objects (especially from the light polluted suburbs in which most of us live), but I was able to track down some of the brighter galaxies, m51, m65 & m66 and a selection of the brighter planetary nebulae. Unless you live under dark skies or have the patience of a saint this scope will probably get the very large majority of its use on the planets and the moon. As the 102 is achromatic it has the potential to be quite contentious amongst observers. Achromatic refractors are made by uniting two different lenses which disperse light differently, these refractors bring red and blue light to focus in the same spot, therefore creating a purple halo around any object being observed. The brighter the object the more pronounced this purple colour (or chromatic aberration as it is known). There are some who cannot tolerate CA and there are some (like me) who really don't mind it, either way it's something worth considering before you lay out the £380-£400. Having said that I don't mind chromatic aberration in visual astronomy, I do find it bothersome when imaging solar system objects. Using my modified fusion webcam to image Jupiter does produce some strange colours and a bright blue ring around the planet. For astrophotography you would be better off with the ED version of the 102. Using a more expensive, lower dispersion glass to minimise CA but nearly doubling the price of the scope in the process. Only you will know if CA will prove to be a distraction for you but if you can put it out of your mind you'll be seduced by the crystal clear, pin sharp views afforded by this little refractor. Details within the Jovian atmosphere are prominent and awe inspiring, Saturn reveals its Cassini division with no effort and the lunar surface is a cornucopia of rilles, craters and valleys. I really love the 102, on the strength of it's quality optics, covered in Celestron's much championed XLT starbright coatings. The full multi coating is made from Aluminum, Hafnium Oxide, Titanium Dioxide, Silicon Dioxide and Magnesium Fluoride and offers views that are 11% brighter than a regular UHTC coating. Although this is just an interesting piece of trivia what it means in reality is that all lense elements on the 102 are highly reflective at 95%. To put it another way, the optics of the 102 are top notch, collecting and commanding almost every photon that hits its surface. With a perfectly functional 6x30 finderscope which is more than enough for solar system work and sitting upon the trusty CG-4 German equatorial mount, the 102 is a joy to look through and operate, it is kept from perfection within its low price band by a somewhat dodgy focuser. Using a rack & pinion design which utilises gears and teeth rather than a pressured smooth wheel (like the more reliable crayford design of focuser) makes for alot of play in the drawtube. The focuser can actually be wiggled around and can become wonky, producing uneven focusing. As much as I love the optics of this thing the focuser is pretty heinous. I am going in with some friends to replace the focuser with a lovely smooth 10:1 crayford that I know works wonderfully. To conclude, this is a formidably good telescope, optically and aesthetically. Its failing is the focuser which will need to be upgraded, there are some lovely Crayfords available sub £120. Once a new focuser has been added, the 102 will continue to wow you with its high class performance, well recommended.

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