The eyepiece is around 4 inches long and 1.25 inches in diameter so it will fit in any standard telescope. The body of the eyepiece is a cheap black plastic and there’s a hole in the side with a small angled mirror pointing downwards in the direction of the telescope.
Before we go on I should say that to use one of these you must have a little paper doughnut stuck exactly onto the centre of your primary mirror, most telescope manufacturers put one on for you but if they haven’t it’s essential you do it yourself, but that’s a whole other review.
When collimation is necessary just pop the eyepiece into your telescope and look out for the tiny black dot. The idea is to get this black dot to fit perfectly inside the paper ring by moving the primary mirror.
You have two choices when it comes to collimation, either you do it during the day, the light making it easier to see the black dot and the paper ring, the downside being that it is then impossible to do a star test* to check the accuracy of your collimation. It also leaves your telescope stranded outside for hours on end before you use it, vulnerable to the unpredictable English weather.
If you wait until night time so that you can use the stars to help collimate as well as the eyepiece then you can use a torch shone at the angled mirror to see the black dot and doughnut. This works fantastically, it does ruin your dark adaption making your pupils shrink to pin pricks but as you’ll be collimating at the start of an observation session then this isn’t a problem.
The eyepiece offers many advantages over both laser collimation and naked eye collimation. Advantages over the laser are numerous…
-Collimation Eyepiece Vs Laser-
. No lasers means no chance of blinding yourself
. No fiddling about with tools before you can use it
. Can be accurately used straight out of the box, No messing about
. Lighter
. More compact
. Collimation Eyepiece doesn’t malfunction or inexplicably stop working
. Eyepiece is more robust, will take a few drops on the ground
The eyepiece even has some advantages over using just your eye up against the focusing tube…
-Collimating Eyepiece Vs Naked Eye-
. Tiny hole in CE forces your eye to look only at the centre of the primary (Naked eye is wildly inaccurate as results can dramatically change simply by shifting your eye a few centimetres)
. Angled mirror means with the addition of a torch (red light if possible as this doesn’t ruin your dark adaption as much as blue or white light) you can easily collimate in the darkest of conditions
. Black dot is a smaller target than your own eye blinking back at you, smaller target means more accurate collimation
What makes the Collimation Eyepiece (or Cheshire as it’s sometimes known) so brilliant is its simplicity. Cheaply made but highly accurate and durable. Reliable, no arsing about trying to centralise laser beams. Can be used straight out of the box.
Basically it’s never let me down, I’ve collimated hundreds of times with it and it’s efficient, practical design has ensured each time I have has been as easy as counting the rings on Jupiter 8^)
* A star test is conducted by pointing at a bright star with a regular eyepiece at high magnification, the pattern the star displays when slightly out of focus will alert you to any further fine tuning to your collimation.
