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.