In some ways, it's a bit of a fallacy
that a laser collimation tool is the answer to perfect collimation
because there are indeed many factors involved that may cause
deviations from a perfect result. They are essentially a convenient
way to tweak slight mirror shift that may occur when in the field
after your telescope has been transported, bumped, knocked etc to
fine tune for the mirror mounting deviations that can occur.
collimations tools are excellent for achieving optical alignment of your
telescope after the instrument has already mechanically mirror plane
aligned. However some laser collimation products don't come with instructions so we provide this following
guide to help you. You should first check out your telescope manual
about mechanically centring the primary and secondary mirrors before
using a laser collimation device. See also our
initial Newtonian / Cassegrain collimation guide here
laser collimators themselves
must be checked for correct collimation before use. Most high end
laser collimation devices like the
self-centring HOTECH and others are preset at the factory for perfect
collimation but can shift from perfect over time due to bumping
during transportation, dropping and even the subtleties of heat
cooling and contraction with general use over time. AstroShop's
policy is to check new laser collimation devices before shipping to our customers
and you can see this at our
YouTube video site.
Laser collimators generally go out of
alignment themselves because the are suspended within a metal housing with a red laser head fitted inside which is supported
by a rubber "O" ring and pivoted by
three or six tiny screws. But, they can be adjusted just like the way you align a finderscope
and or the primary and secondary mirrors of you telescope.
See a video
demonstration of the HoTech collimation tool here.
Just like delivering a Newtonian or Cassegrain optical telescope,
perfect collimation due to the reasons pointed out above cannot be
guaranteed and the user must learn to make adjustments to the laser
collimation device itself (just like the telescope) when or if
There are a few variables you need to
consider that might affect the result you are interpreting when
using a laser collimation device.
A.) Correct Primary & Secondary
initial optical alignment
B.) Flopping (weight shifting) of the primary or even secondary
mirror mountings at different positions
C.) Shifting of the focuser due to less than best construction or
D.) Your laser itself is out of collimation (internal laser
adjustment) or not seated flat to the focuser base.
If you have a V-Block or V-shaped mini wine rack (like I use) you simply lay the
collimator horizontally along it. Turn on the laser and direct the red dot beam to a point
on a wall say 4 or 5 meters away. You can sticky tape a piece of paper at this spot and
draw a circle around the projected laser dot. If you wish to have it super accurate then
the further away the wall is, the larger will be the noted circular pattern or deviation
from absolute centred. Another useful tool is to use a quality
rotatable focuser like a Moonlite and others that allow for smooth
360 degree rotation of the fitted laser collimating tool.
Turn the laser collimator through 360
degrees. If it is well collimated you should see that the dot stays fairly well
within the tiny drawn circle or does not deviate from the dot reference mark on the paper.
If not you need to adjust the collimation of the laser head. In our Optex laser collimator
you will notice it has three Allen key grub screws that can be adjusted to pivot the
internal laser head to the correct central position.
Just make small adjustments on each axis (one at a time) to see if the projected dot at
your reference point deviates more or less. In other words, as you turn the laser
collimator on its axis, if the laser dot produces are larger circular pattern then you are
adjusting the wrong way and should back of the last adjustment. If the laser dot traces
out a smaller circular pattern as you turn the collimator then you are heading in the
Once no deviating circular motion occurs
when turning the collimation tool on its horizontal axis then it can now be used at the
HOTECH Collimator - requires 1.3mm or 0.05" Allen key to make
Above: FarPoint and other typical laser collimators
After inserting in the focuser red laser,
check secondary mirror alignment by looking down main tube to see if the red dot is in the
centre of the black centre primary mirror marker. If not simply adjust the three tilt
screws on the secondary mirror until the red dot falls on the primary mirror marker.
NOTE: If there is any slack in your
telescopes focuser then this will alter accuracy of the collimation result. Be sure the
laser is set into the focuser both flat and firmly tightened into place.
To adjust the main mirror turn the collimation tool around so the angled Cheshire is
facing towards the back of the telescope. From here you can see the red dot on the
Cheshire. The idea is that the beam must fall back in on itself. If it's out of alignment
then you'll see the red dot on the metal Cheshire surface. By making adjustments
to the primary mirror thumb screws you will see which direction the
red dot is moving on
the Cheshire face. Adjust until the beam falls inside the laser collimator central hole.
Check at the front of the scope again and make sure red dot is still on centre mirror
marker. If so, then you have a well collimated instrument.
DEMONSTRATION VIDEO OF
THE HOTECH LASER COLLIMATOR
your laser collimator can reveal
Aside from revealing
how far out of collimation your telescope may be, a good laser
collimation tool can reveal other defects in the optical train you
sometimes don't expect. Things such as mirror flop, wobbly focuser
or focuser assembly not seated flat to the optical tube. To check
for mirror flop or sloppy focuser, (in the case of a Newtonian for
example) after an initial collimation adjustment, move the telescope
around on different angles looking from the rear of the instrument
at the cheshire. If you notice that the red dot moves out from the
central hole from where you had originally aligned to then it's
likely the mirror is shifting in its mounting cell. The other
possibly cause may be that shifting weight distribution at the
focuser is revealing slop in the focuser shaft or fixtures. First
re-check that the laser collimator is firmly fitted and tightened in
the focuser. If so, lightly press against the rear mirror at various
points while looking up at the laser collimator cheshire. If the red
dot shifts then you know you have a little mirror flop occurring
that will need adjustment for firm seating.
If the mirror seems
ok, try applying a little pressure to the focuser drawtube - If any
shift occurs then it should be tightened, padded out or simply
replaced whatever the case my call for.
If you're unable to
do it yourself, you are welcome to bring your laser collimation tool
into our workshop for adjustment at no cost or for the cost of
return postage and packaging if sending by post.