* Astronomy

The Seben Laser Collimator is a class IIIa 650nm red laser (1 - 5mW) to help with the accurate collimation of your reflector telescope.
The laser is designed to fit into a standard 31.7mm (1.25") focus tube; some package deals including a 2" adaptor.
It is powered with a standard CR2032 3V lithium battery, accessed by a threaded endcap; Early versions have a clearly marked ON/OFF switch incorporated into the rotating end ring. In newer versions, the rotating ring incorporates 7 power levels for adjusting the laser intensity levels; 0 being the off position. High power (7) is slightly fuzzier than the low power settings, but bright enough for easy daytime collimation.

A 45 degree white target reticle plate shows the reflected laser dot clearly. You can turn the collimator in the eyepiece holder so you can see the white target while adjusting the main mirror. 

Reassuringly, the Seben Laser Collimator has a solid die-cast aluminium body. The length is 4".

To get the best image from your reflecting telescope you need to accurately align your telescope mirrors regularly, and a laser collimator is helpful for this purpose. Similarly, the collimator can be used to assist in realignment of refractor objective lenses (so they are sitting accurately in their lens cells).
The Laser Collimator is suitable for Newtonian reflectors, Dobsonians, Refractors and (to a lesser extent) Schmidt-Cassegrains. It should be noted that some reflectors use an internal corrector lens inside the focuser, which leads to a fuzzy laser reflection. 

The laser collimator can itself be aligned. Three 2mm Allen key screws around the body (two hidden beneath plastic fillers, and one under the silver warning label) can adjust the pointing of the laser.  After receiving the laser from Seben i discovered that the pointing was slightly off; the laser drawing a 1cm circle at a meter (simply checked by placing in an already collminated reflector). Rolling the laser on the slats of a firm and stable chair, a slight 1/8th turn on one screw, using a 2mm allen key, aligned the laser to a point 4 metres away in a darkened hallway. However, such precise laser collmination is usually not necessary, as it should be delivered reasonably aligned. 

To make sure the laser beam leaves the collimator exactly parallel to the body of the collimator, a small jig can be made to test the pointing accuracy. 

Collimating A Laser Collimater
 

Spoiler

Once realigned, handle with care.

When collimating your telescope, remove any star diagonals and filters.
Make sure the laser collimator is sitting centrally at the optical axis in the focus tube and/or eye-piece adaptor. If you can wiggle it about in the focus tube, the laser dot cannot be trusted to be at the centre of the primary mirror. Lightly tighten the eye-piece adaptor grub screws so as not to push the collimator against the side of the adaptor and away from the optical axis. A self centring focuser adaptor is recommended. It is important to place the telescope tube in a horizontal position, with the focuser upright.

Collimating your reflecting Telescope

Spoiler

Price ~£24

There were no instructions included.

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Bottom line; buy it.