Collimation of the optical system – Leisure Time LX20 User Manual

Page 51

Advertising
background image

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.

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.

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.

52

Advertising