Collimation Of The Optical System - Meade LX200 Instruction Manual

environmental pollutants, or temperature changes reacting with
the interior paint, causing outgassing or water condensation, or
combinations thereof.
It is possible to clean the interior of the optical system yourself
or to have it done professionally. In the case of the former, take
great care in handling the optics. Any impact or rough handling
can damage the surfaces, which may require complete optical
replacement at Meade Instruments at substantial cost. Meade
Instruments assumes no liability for damage incurred to the
telescope by the customer.
The cleaning techniques described above are used while
cleaning the interior of the optical system, with one exception:
Do not apply cleaning solutions to the front surface
mirrored optics. Only use the soft camel hair brush and the
suggested ear syringe for removing particles. The corrector
plate can be cleaned in the normal manner.
To remove the corrector plate, follow the instructions below:
a. Remove the six (8" and 12" models) or the eight (10"
model) stainless steel screws that hold the corrector plate
retaining ring with the raised white lettering in place. This
should be done with the Drive Base placed flat on a work
bench, and the optical tube assembly pointed up at a 45-
degree angle with the declination lock secure to prevent
accidental dislodging of the corrector plate.
b. Remove the plastic retaining ring and locate the two white
alignment marks, one at the edge of the corrector plate
lens and one beside it on the black metal front cell. These
two marks line up and serve as the precise rotational
position of the corrector plate in the optical train. If no
marks exist, make them yourself with a small paintbrush
and some white paint, so that when you return the
corrector plate to the front cell you are putting it back in
the same position that you took it off.
c. Remove the corrector plate from the telescope, holding it
by the plastic central secondary housing. Gently flip it over
so that the secondary mirror is facing you, then reinsert
the corrector plate back into the front cell. This will allow
you full access to clean the interior optical surfaces
without touching them with your fingers.
d. When cleaning is complete, replace the corrector plate in
it's original position, carefully lining up the rotational index
marks described in paragraph b, above. Then replace the
retainer. Partially thread in all of the stainless steel
screws, then, one at a time, snug the screws down to
prevent the corrector plate from rotating in the front cell.
Take care not to overtighten the screws as it will stress the
corrector plate lens.
e. A final check of the optical system is to inspect for proper
collimation (alignment) of the optics.
1
3
Fig. 26: Collimation of the Optical System. (1), (2), (3) Set
screws for adjusting collimation.
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2

2. Collimation of the Optical System

The optical collimation (alignment) of any astronomical
telescope used for serious purposes is important, but in cases
of the Schmidt-Cassegrain design of the 8", 10", and 12"
LX200, such collimation is absolutely essential for good
performance. Take special care to read and understand this
section well so that your LX200 will give you the best optical
performance.
NOTE: The 7" LX200 does not require collimation.
For final optical tests, every Meade Schmidt-Cassegrain is
precisely collimated at the factory before shipment. Our
company is well aware that through shipment and normal
handling, the optical alignment can be degraded. The design of
the optical support system make the method of collimation easy
to do. Even the uninitiated can make an alignment of the optics
to the same high precision that is performed at the Meade
Instruments Optical Laboratories.
To check the collimation of your LX200, center a bright star that
is overhead, or use a reflected "hot spot" of reflected sunlight
from a chrome car bumper or a telephone pole insulator, with
the supplied 26mm eyepiece. To make a correct evaluation of
the alignment it helps if the telescope has been allowed to
either cool down or warm up to the ambient temperature where
the instrument is set up. Temperature differences between the
optics and the outside air can cause distortion in the images.
With the star or hot spot centered, de-focus the image. You will
notice that the out of focus star image looks like a ring of light
(the dark center of the ring is the shadow of the secondary
mirror). Turn the focus knob until the ring of light fills about 1/8th
of the eyepiece field. Take note that if you keep de-focusing the
star past about 1/8th of a field, that the ring will look perfectly
concentric (even on all sides) even if the optics are out of
alignment, thus preventing you from seeing any misalignments.
If the ring of light does not seem to be even on all sides, or if
the dark center seems to be offset in the in the ring of light,
follow the method below:
a. To make collimation easy, the only adjustments possible
on the 8", 10", and 12" LX200 come from the three set
screws (1, 2, and 3, Fig.26) located at the edge of the
outer surface of the secondary mirror housing.
WARNING: DO NOT FORCE THE 3 COLLIMATION
SCREWS PAST THEIR NORMAL TRAVEL AND DO NOT
LOOSEN THEM MORE THAN 2 FULL TURNS
(COUNTER-CLOCKWISE
SECONDARY MIRROR MAY COME LOOSE FROM ITS
SUPPORT. YOU WILL FIND THAT THE ADJUSTMENTS
ARE VERY SENSITIVE: USUALLY, ONLY TURNING A
COLLIMATION SCREW 1/2 A TURN WILL GIVE
DRAMATIC RESULTS.
b. While looking at the de-focused star image and noticing
which direction the darker shadow is offset in the ring of
light or noticing which part of the ring is the thinnest
(1, Fig. 27), place your index finger in front of the
telescope so that it touches one of the collimation set
screws. You will see the shadow of your finger in the ring
of light. Move your finger (or an assistants finger) around
the edge of the black plastic secondary mirror support
until you see the shadow of the finger crossing the
thinnest part of the ring of light. At this point, look at the
front of the telescope where your (or your assistants)
finger is aiming. It will either be pointing directly at a set
screw, or it will be between two set screws aiming at the
set screw on the far side of the black plastic secondary
mirror support. This is the set screw that you will adjust.
c. Using the telescope's slow motion controls, move the de-
focused image to the edge of the eyepiece field of view
(2, Fig. 27), in the same direction as the darker shadow is
offset in the ring of light.
DIRECTION), OR THE