Adjusting A Newtonian Telescope - Omegon EQ-1 Mode D'emploi

4.2 Adjusting a Newtonian telescope

A Newtonian telescope needs to be adjusted now and again. Only when well collimated will the optics provide
you with optimal performance and can you benefit from a sharp and a high contrast view. The telescope mirrors
will have been pre-set at the factory, but transport can throw this off slightly. Before you begin with the adjustment,
it is a good idea to check whether the mirrors actually are out of alignment. In order to discover this, find the polar
star with your telescope, centre it in the field of view and defocus it.
Indications that the mirrors are in collimation:
The star has now become a round shape with a black circle in the centre. You could compare this shape to that
of a donut. Now pay particular attention to the central area shading, this should be precisely in the centre of the
disc. In good seeing conditions you will also be able to see several concentric symmetrical diffraction rings.
Indications that the mirrors are out of collimation:
The star has now become a round shape with an interior black circle. However, the central shading is no
longer exactly central but has shifted to one side. The diffraction rings around the shading are also not arranged
symmetrically.
If collimation is required:
Remove the telescope tube from the mount and place it horizontally on a table with the focuser pointing
upwards. Remove the objective and eyepiece covers. Look into the front opening of the telescope. You will be
able to see the main mirror at the bottom, which is fixed with three holding clamps. In the front part of the tube
you will see secondary mirror spider with a small plane mirror positioned at 45°. This has the task of directing
the light bundle into the focuser.
In the centre of the mirror spider you see three small screws, which are for adjusting the attitude of the
secondary mirror. At the lower end the tube you will see three or six screws for the adjusting the main mirror.
Turning these screws changes the tilt orientation of the mirror and hence the state of adjustment.
correctly adjusted has to be collimated
main mirror secondary mirror
focuser
secondary mirror cell
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