Collimation (Alignment) Of The Optical System - Meade LX200 Instruction Manual

You can clean the interior of the optical system yourself or have
it done professionally. If you do it yourself, handle the optics
very carefully. Any impact or rough handling can damage the
surfaces. This may require complete optical replacement at
Meade Instruments at substantial cost. Meade Instruments
assumes no liability for damage caused by the customer.
The techniques described above are used while you clean the
interior of the optical system, with one exception: Do not apply
cleaning solutions to the front surface mirrored optics.
Use only the soft camel-hair brush and the ear syringe for
removing particles. You can clean the corrector plate in the
normal manner.
To remove the corrector plate, follow this procedure:
1. Remove the six stainless-steel screws that hold the
corrector-plate retaining ring with the raised white lettering in
place. Do this with the drive base placed flat on a work
bench and the optical tube assembly pointed up at a 45°
angle, with the Dec. lock secure to prevent accidental
dislodging of the corrector plate.
2. Remove the 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 there are no marks,
make them yourself with a small paintbrush and some white
pain so you can return the corrector plate to the front cell in
the same position from which you removed it.
3. Remove the corrector plate from the telescope, holding it by
the plastic central secondary housing. Gently flip it over so
that the secondary mirror faces you, then reinsert the
corrector plate back into the front cell. This allows you full
access to clean the interior optical surfaces without touching
them with your fingers.
4. When cleaning is complete, replace the corrector plate in its
original position, carefully lining up the rotational index
marks described above. Replace the retainer. Partially
thread in all 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 this will stress the corrector plate lens.
5. A final check of the optical system is to inspect for proper
collimation (alignment) of the optics.

Collimation (Alignment) of the Optical System

The optical collimation (alignment) of any astronomical
telescope used for serious purposes is important. With the
Schmidt-Cassegrain design of the 16" LX200, such collimation
is essential. Read and understand this section so that your
LX200 can give the best optical performance.
For final optical tests, Meade precisely collimates every
Schmidt-Cassegrain at the factory before shipment because
shipment and normal handling can degrade the optical
alignment. The design of the optical support system simplifies
collimation. Even the uninitiated can collimate 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 hot spot of sunlight reflected from a
chrome car bumper or a telephone-pole insulator, with the
supplied 26mm eyepiece. To evaluate the alignment, let the
telescope 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 distort the
images.
With the star or hot spot centered, de-focus the image. You will
notice that the unfocused 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. If you keep de-focusing the star past
about one-eighth of a field, the ring looks perfectly concentric
(as in 3, Fig. 16) even if the optics are out of alignment, thus
preventing you from seeing any misalignments. If the ring of
light does not appear concentric or if the dark center appears
to be offset in the in the ring of light, follow this procedure:
1. To make collimation easy, the only adjustments possible on
the 16" LX200 come from the three set-screws (shown in
Fig.15) located at the edge of the outer surface of the
secondary mirror housing.
1
Fig.15: Collimation of the optical system.
(1), (2), (3) Set-screws for adjusting collimation.
2. 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. 16),
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
have an assistant move a 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 assistant's) finger is aiming. It is either pointing
directly at a set-screw or it is 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.
CAUTION: DO NOT FORCE THE THREE COLLIMATION
SET-SCREWS PAST THEIR NORMAL TRAVEL AND DO
NOT LOOSEN THEM MORE THAN TWO FULL TURNS
(COUNTER-CLOCKWISE)
MIRROR MAY COME LOOSE FROM ITS SUPPORT. THE
ADJUSTMENTS ARE V E RY SENSITIVE. U S UA L LY,
TURNING A COLLIMATION SCREW ONLY ONE-HALF A
TURN GIVES DRAMATIC RESULTS.
3. Using the telescope's slow motion controls, move the de-
focused image to the edge of the eyepiece field of view
(2, Fig. 16), in the direction that the darker shadow is offset
in the ring of light.
4. Turn the set-screw that you found with the pointing exercise
while looking in the eyepiece. Notice that the star image
moves across the field. If, while turning, the out-of-focus star
image flies out of the eyepiece field, you are turning the
screw the wrong way. Turn in the opposite direction and
bring the image to the center of the field.
2
3
OR THE SECONDA RY