Celestron 82291 User Manual

Adjustment (Collimation) of

Newtonian- and SC-Telescopes

Instruction Manual

BAADER PLANETARIUM

with the help of the

TM

LASER-COLLI

by Baader Planetarium

 2005 by Baader Planetarium GmbH

Zur Sternwarte • 82291 Mammendorf • Tel.[phone] • Fax [phone]

www.baader_planetarium.de • [e-mail] • www.celestron.de

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Adjustment of Newtonian Telescopes with the

Laser-Colli™ by Baader Planetarium

Caution: LASER !

Never ever look directly into a laser beam! Protect your eyes!!
Store the Laser-Colli™ carefully so that it cannot be reached by
children or inexperienced adults. Consider that a heavily
Miss-aligned telescope will deflect the laser beam out of the tube
In an unpredictable direction possibly without you being aware of it.

Colli is the abbreviation for collimation.
In our context collimation is the alignment of the optical system so that the focal plane
of the telescope meets the focal plane of the eyepiece squarely.
Collimation is critical for good optical performance of your telescope.
Accurate collimation can be the difference in seeing or not seeing the Great Red Spot
and shadow transits of Jovian moons on Jupiter

Generally Newtonian telescopes are considered susceptible to a loss of image quality (collimation)
if, for instance, they are jarred or bumped, during transport by car etc. If this is a situation that you
have come across then a Laser-Colli™ will be a basic accessory to keep your telescope perform­ing at it’s best. With a little preparation and a bit of practice your telescope will be correctly colli­mated within a minute or two.

A Newtonian telescope can provide you with excellent images of astronomical objects – but only if
the primary mirror (concave parabolic mirror at the rear end of the tube) and the flat secondary
mirror (catching and deflecting the light out to the side of the tube and into your eyepiece) are cor­rectly aligned with each other and additionally centered on their optical axes.

Let’s have a look again at the light path of a Newtonian telescope.

The incoming light travels first from left to right to the main mirror at the end of the tube,

is reflected there and travels right to left, to the secondary mirror, which in turn deflects

the light out of the tube and – via the eyepiece – into your eye.

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Loss of collimation is an important factor to be aware of with telescopes of any design if perform­ance ‘falls off’ at any time.

A refractor’s eyepiece tilted within its eyepiece holder will show the same low quality blurred im­ages. This holds true with all other mirror telescope systems like the popular Schmidt-Cassegrain
or Maksutov systems.

The following will guide you mainly through the collimation of a Newtonian telescope.
At the end we shall consider Schmidt-Cassegrain systems and other catadioptric instruments.

If misalignment exists in a Newtonian telescope the main image error - ‘so-called’ coma – will be
enlarged greatly and is even visible at the center of your field of view whilst normally it can be seen
only at the edges.

Please note: The larger the diameter of the main mirror and the shorter the

focal length of the optical system, the more the telescope is affected by a
small loss of collimation.
As an example: A Newtonian with a main mirror diameter of 200 mm and a
focal ratio of f/10 (2000 mm focal length) is less influenced by a slight mis­alignment; a Newtonian with 400 mm diameter mirror and a focal ratio of f/5
(same 2000 mm focal length) however is 4 times more affected by the same
collimation error .

Picture above shows coma error, strongly exaggerated.
Thermal turbulences blur the image to a “small comet’s trail”.

The following procedure assumes a mass marketed telescope for collimation.
Owners of homemade mirror telescopes will need to know how to collimate.

To obtain best results from collimation:

1.) The focuser (eyepiece holder) must be orientated exactly 90° vertically to the tube.

2.) The main and the secondary mirrors must be centered in the tube.
Mass marketed telescopes should fulfill both requirements. The correct center of the main mirror is

(nearly) always guaranteed by the mechanical construction of the main mirror’s cell within the tube.
The secondary mirror often can be adjusted slightly in its center position via three or four of its
vanes. With a newly bought system you can assume a correct center position. If it is not centered
this does not result in a loss of quality of the image in any case but your field of view might become
darker.

What is the function of our Laser-Colli™?

The principle is simple. The normal eyepiece (ocular) is removed and the Laser-Colli™ is slid into
the eyepiece holder and switched on. The laser beam hits the secondary mirror and is reflected
back to the main mirror, from where it is reflected again to the secondary mirror and then back into
itself through the eyepiece holder. If either or both of the mirrors are displaced from the optical axis
of the telescope system, the laser beam cannot be reflected into itself.

If the beam is reflected into itself your Newtonian system is perfectly collimated.
More often than not, this is not the case – and collimation is necessary.

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Of course, the Laser­Colli™ functions reliably

only if the laser beam it­self leaves its own hous­ing in an absolutely cen­tered position.

Therefore the laser source
is symmetrically adjust­able in the housing around
its rotational axis, which
has been carefully ad­justed on a mechanical
lathe by us prior to ship­ping - also see following
page.

The six headless setscrews serve the purpose of adjusting the laser exactly co-axial. Please –
never try to tweak these screws yourself otherwise the laser will become tilted in its housing
and thereby misaligned. For the same reason the orientation of the Laser-Colli™ in the ocular
holder of the telescope is of utmost importance.
A few more explanations and pictures follow:

Orientation of the Laser-Colli™ in the eyepiece holder

All our Laser-Colli™ instruments are individually adjusted in an eyepiece holder on a lathe for the
required centered rotational symmetry. Necessary mechanical production tolerances for the ocular
holder and the housings of our Laser-Colli™ instruments require a correct orientation when
mounting the Laser-Colli™ into your eyepiece holder as shown below.

Please see the picture on the left:
The rear screw serving as On-Off switch for the laser
beam should be aligned with the locking screw on the
ocular holder.
If your telescope has two or more locking screws 120°
apart of each other, the rear On-Off switch screw of
the Laser-Colli™ should be orientated on a center
line just between them.

This orientation guarantees the laser alignment to be
identical to the one in your eyepiece or camera to a
fraction of a millimeter.

The Laser-Colli™ will be switched on by turning the
small thumb screw (see picture). Thereafter the laser
beam passes through the small hole in the center of
the glass reference (see picture below). The reference
has been etched with a very fine grid.