Meade 6" ETX-LS ACF Instruction Manual Download

Page: 34 / 45

eyepiece field of view

(

Fig. 8, 2

), in the same

direction as the darker shadow is offset in the
ring of light.

Turn the set screw that you found with the

pointing exercise while looking in the eyepiece.
You will notice that the star image will move

across the field. If while turning the defocused
star image flies out of the eyepiece field, then

you are turning the screw the wrong way. Turn
the opposite direction and bring the image back

to the center of the field.

If the screw you are turning becomes very loose,

tighten the other two screws by even amounts. If
the screw you are turning gets too tight, un-thread
the other two by even amounts.

When you bring the image to center (

Fig.

8, 3

), carefully examine the evenness of the ring

of light (concentricity). If you find that the dark

center is still off in the same direction, continue to
make  the  adjustment  in  the  original  turning
direction. If it is now off in the opposite direction,
you have turned too far and you need to turn in
the opposite direction. Always double check the

image in the center of the field of the eyepiece.

You may find after your initial adjustment that the

dark center is off in a new direction (e.g., instead
of being off side-to-side it is now off in an up-and-
down direction). In this case repeat steps 2
through 6

to find the new adjustment screw.

Now try a higher power eyepiece (e.g., 9mm or

less)  and  repeat  the  above  tests.  Any  lack  of
collimation  at  this  point  will  require  only  very
slight adjustments of the three set screws. You
now have good collimation of the optics.

As a final check on alignment, examine the star

image  in  focus  with  the  higher  power  eyepiece
as  suggested  above,  under  good  viewing
conditions.  The  star  point  should  appear  as  a
small  central  dot  (commonly  referred  to  as  an
“Airy disc”) with a diffraction ring surrounding it.

To give a final precision collimation, make

extremely  slight  adjustments  of  the  three  set
screws, if necessary, to center the Airy disc in the
diffraction ring. You now have the best alignment
of the optics possible with this telescope.

dark central spot is in fact the shadow of the secondary

mirror. Turn the focus knob until the ring of light fills
about 10% of the eyepiece field-diameter. If the dark

central spot is offset in (i.e., not concentric with) the ring
of light, your telescope’s optical system is misaligned
and requires collimation.

Follow these steps for collimation of the
optical system:

The only adjustments possible, or necessary, on

the LS-6 are from the three inner most screws

located at the inner surface of the secondary
mirror housing.

CAUTION: Do not force the three collimation screws
past their normal travel and do not loosen them
more than two full turns in a counterclockwise
direction or the secondary mirror may come loose
from its support. You will find that the adjustments
are very sensitive, usually requiring only one-half
turn or less to produce the desired result.

While looking at the defocused star image, notice

which direction the darker shadow is offset in
the ring of light or notice which part of the ring is
the thinnest (

Pg. 32 Fig. 8, 1

). 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 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 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.

Using the Arrow keys at the slowest slew speed,

move the defocused image to the edge of the

MAINTENANCE

Collimation Screws