One of the activities that every amateur astronomer should run it on your telescope, in order to benefit from a powerful tool, is the collimation of the optics. To do this there are several techniques, exploiting other devices, like a needle pierced or port a Cheshire collimator or autocollimator or through the Star Test, or by using a laser collimator.
The latter type of collimator, is positioned in the Focuser in place of the eyepiece and uses a laser beam that, bouncing before the secondary mirror, on primary and secondary again, allows you to adjust the tilt of mirrors, so that the beam of return is exactly superimposed on the starting RADIUS. When this happens the optics are exactly mutually orthogonal and Collimation was reached.
The laser collimator allows a quick setting of the instrument (It will be always checked at the star test) provided of course, the laser beam emerging from the collimator, is perfectly coaxial to it.
If the scope is not "collimated" , because the laser beam is not perfectly coaxial with the barrel that slips into the Focuser, the resulting collimation cannot be optimal, Since the optics of the primary and secondary are you perfectly mutually orthogonal, But even with the eyepiece axis.
If you rotate the scope about its axis, While it is still plugged into the Focuser, You should observe, the bright dot, produced by laser beam, does not move. If this happens and describes a circle, This indicates that there is an angle between the barrel axis and the axis of the laser beam collimator, that needs to be eliminated through the 3 small screws adjustment (attention: often the housing of small screws is filled with silicone. If you have to act on them you will need to remove it).
One way to check, and possibly coincide easily collimator, is to make a device like the one shown in the following figure, formed by a base, two bearings 6007 internal diameter 35 mm, two supports for the bearings and bushings to fit the barrel outside diameter 31.8 mm collimator with 35 mm inner diameter bearings.
At this point just tuck the collimator in the bosses and observe the movement of the bright dot collimator to rotate around its own axis.
Once inserted the collimator in bearings, fix the base of the device on a table, Vice or any other medium, so that the laser pointer can project its beam on the wall of a distant wall 4-5 meters.
Now just turn on the laser and mark with a pencil where the laser beam is projected on the wall. That is done turn the scope around its axis by 90°, and mark with a pencil the new point where the laser beam is projected on the wall (probably different from its previous value). Then repeat twice more the increasingly turning 90° the scope with respect to the previous position.
After you perform the same procedure for all four positions, connect with a line, two by two points found, in order to obtain a cross. The point of intersection of the lines, It will be the point at which you will have to drop the laser beam by adjusting the relative small screws, to obtain the collimator sight.
If the adjustment was performed with care, rotating the collimator again around its own axis, you will not notice a significant movement of red dot projected on the wall.
The following video is shown above, to try to make it as understandable as possible the procedure to be run: