 |
Cheshire Collimating Eyepiece
by Revier
If you own a Reflecting telescope (and to a lesser extent a Schmidt Cassegrain) then chances are you will at some point have been forced to tackle that dreaded process that puts off many a newcomer to the hobby...Collimation!!!
Simply put, collimation is the process whereby the small secondary and larger primary mirror are ... aligned in such a way as to deliver the maximum of light from the object being observed into the astronomers keenly waiting eyeball.
It can be the cause of much distress as the whole process can be fairly fiddly and time consuming and unless you have the right tools it can be very hard to know if you're doing it right.
That's why a simple piece of equipment like the humble 'Cheshire' can make all the difference. When the Cheshire is inserted into the focuser (in exactly the same way you'd insert your regular eyepieces) and the observer peeps through the tiny pin hole of the eyepiece they are presented with a field of view that is only marginally bigger than the secondary mirror. It then becomes much easier to gauge whether you have manipulated the secondary correctly. Judging whether the secondary appears perfectly rounded and centred is easier when you have a slightly larger concentric circle (that of the field of view) to judge against.
A black cross-hair built into the eyepiece makes it easy to centralise the paper doughnut (or central mark) of your primary mirror. But the best thing about the Skywatcher is its 45 degree tilted built in mirror which- with the addition of a suitable red bulbed torch- will allow you to collimate out in the field even at night.
The simplicity of the Cheshire's design belies its indispensable nature, before you shell out for an expensive collimating laser be sure to get yourself one of these, many astronomers (myself included) find that the simpler and cheaper Cheshire will provide more accurate and reliable results, and the Skywatcher is a perfectly good example of its kind.
When you consider the Skywatcher Cheshire is available for under £30 (compared to several hundred at the top end of the scale) and it does it's job just as accurately, just as consistently as any of the big boys there should be no need for the perpetually skint astronomer to bankrupt themselves in the pursuit of optimum telescopic maintenance.
Read the complete review |
 |
Revelation Newtonian Crayford Focuser
by Revier
One of the most critical factors in astro imaging alongside good tracking is a decent focus, replacing the factory installed run of the mill rack & pinion focuser on my 12" Dob was one of the first modifications I made to the telescope and all things being equal, was a worthwhile one. I say all things being equal because the ... Revelation has its share of negative points despite getting the job of precise focus done.
Firstly and most importantly, the 1.25 inch adapter (where you insert eyepieces) is absolutely useless!!! It is way too tight so as to make regular eyepiece insertion/withdrawal impossible. To secure or remove a camera/eyepiece you must first loosen the tightening screw that anchors the 1.25" adapter to the focuser then withdraw the eyepiece with the adapter still attached like a ballerina's skirt. Then you have to twist the adapter off with a considerable effort. It's unconscionable that such a basic and fundamental error should have made it all the way through to production.
It has to be said though that once you get used to this rather absurd design flaw and the elaborate process of twisting your eyepieces in and out becomes second nature the focusing action itself is very precise for a £120 focuser. As the Crayford design uses a smooth steel roller and pressure to achieve traction (where the traditional R&P focuser uses toothed gears) the focus is wonderfully smooth without any of the wobble or bumpiness associated with the cheaper rack & pinion focusers.
Focus is buttery smooth not only with the large knurled rubber cups that operate the regular action but also with the small button sat on the right hand side that is responsible for the 1:10 fine focus. Getting yourself roughly to the point of focus and finishing off precisely with the fine 1:10 control is an extraordinarily satisfying and tactile experience.
Something to watch out for, make sure you have the correct base plate for the focuser to sit on, if not (as was the case for me) you will be left with two conspicuous gaps either side of the focuser, which as well as being aesthetically unappealing will let in loads of dust unless covered with black tape or some such.
Despite the problems with the 1.25" adapter I would recommend the revelation for the simple reason that it's hard to find a decent focusing action within the budget crayford category, any frustration encountered with the adapter is offset by the super smooth and crisp focus achieved.
Read the complete review |
|
|
National Geographic Land and Sky Telescope
by louisechackett
My son had decided he wanted a telescope to look up at the stars last year and so I had a look online and saw a national geographic endorsed one selling on play.com for a few pence under ten pounds from memory. I thought that the price sounded reasonable as well as the fact that it was endorsed by national geographic too and so I ... ordered it for him.
When the telescope arrived it was packaged nicely in a cardboard box which showed a picture of the telescope on the front, the national geographic name and logo and from memory a nights sky too. My son was eager to get the telescope out of the box and have a play with it so I allowed him to open it straight away. The telescope itself is yellow with a black end and black eye piece. It has the national geographic logo on the actual telescope too. I was quite pleased with the look of the telescope to be honest as it seemed pretty sturdy but looked nice too. The telescope comes with a small tripod too which to be honest isn't wonderful but for the money it was nice to have one included.
Now, our problems started pretty much straight away with the telescope because despite reading the instructions it took quite a long time to get any focus whilst looking through the telescope. The next issue which we had was simply that my son couldn't see anything in the sky with the telescope! Now somewhat naively I had presumed that my son would be able to have at least an average look up in to the sky using this telescope but he just couldn't see anything apart from our neighbour's houses! I must have looked like some psycho stalker as I peered out of his bedroom window with the telescope to my eye trying to get some reasonable view for my son! The telescope has a 30mm optical lens and up to thirty times magnification which I guess isn't much at all but I was just expecting a bit more despite the low price....I should have thought a bit more really.
My son hasn't really bothered with the telescope at all since the first week or so that he had it because he can't use it for its intended purpose however sometimes when his friends come round and they play role play type games he will get it out and use it as they pretend to be pirates or what not! The telescope looks quite nice on his window sill in his bedroom but in all honesty it was a waste of money really and I certainly wouldn't advise buying this telescope if you are serious about seeing what is in the sky (though I am sure anyone who is serious about that is reading this and laughing at my naivety anyway!)
I think I was probably swayed by the fact that the national geographic people endorsed this product which is a shame to be honest because it has been a waste of money which will no doubt end up in the bin before long. I would certainly say save your money and don't buy this telescope.
Thank you for reading my review!
Read the complete review |
