Collimation - Takahashi Mewlon-180C Instruction Manual

Collimating the optical axis of the Mewlon-180C is made possible by adjusting the tilt the
secondary mirror. Therefore, you will have no such troublesome works as in the Newtonian
telescope. The secondary mirror is an expanding optical system so that it is so sensitive to
the collimation that a slight movement of the adjusting screw can make the optical axis out
of order, resulting in the images degraded greatly.
The Mewlon-180C was checked at each stage of production with a collimator using an
artificial star at the factory. It is collimated a final time before shipment. The optical axis of
the Mewlon-180C is designed to hold collimation and is designed to hold alignment once
collimated, but it might be out of alignment after transporting the telescope. Therefore, in
order to use your telescope to the limit of its potential, you have to always keep its optical
axis collimated. Before you start to do your astronomical observation, never fail to check if
the optical axis is collimated. If it should be found to be misaligned, collimate the telescope
using the following method. The scope should be collimated after about an hour to allow the
optics to equalize with the outside temperature.
1. Remove the spider cover by turning it
as arrowed, then the adjusting screws
are exposed. Be careful not to drop the
cap into the tube when removing the
threaded cover.
2. Select a star brighter (mag 2 - 3) and
higher in the sky and center it at the field
of view.
Focus it by turning the focusing knob and
then defocus in and out from the focal point.
Then, the inner and outer images are seen
with the diffraction rings as shown. If the
optical axis is correctly adjusted, the center
dot, the inner ring, the intermediate ring, and
the outer ring, all form a concentric circle in
the in and out images. In case the optical
axis is decollimated, the center of the circle
is seen off. Then, collimation is required.
(When the focusing knob is turned to "OUT"
position from the focal point, you can see
the inner image. Toward "IN" position, you
can see the outer image.)

Collimation

Optical Axis Collimated
Decollimation can be easily checked with
the image just in front of or behind the focal
point. Off images will appear in the same
direction so either image will do. Remember
in which direction the off images appeared.
- 18 -
Adjusting Screw
Turn
Counter-Clockwise
Spider Cap
Diffraction Ring of Star
Optical Axis Decollimated