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Using a Laser Collimating Tool - AstroShop

 
Using your Laser Collimation Tool
Collimating the Laser Collimator

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. 

Laser 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

Most 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 needed.

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 loose mountings
D.) Your laser itself is out of collimation (internal laser adjustment) or not seated flat to the focuser base.


We recommend you consider buying a copy of this excellent
in-depth guide to telescope collimation.

Adjusting a Laser Collimation Device

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 right direction.

Once no deviating circular motion occurs when turning the collimation tool on its horizontal axis then it can now be used at the telescope.

 


HOTECH Collimator - requires 1.3mm or 0.05" Allen key to make the adjustment.

 

Above: FarPoint and other typical laser collimators



AT THE TELESCOPE

First of all do a visual check to ensure a roughly collimation instrument using your eye as you already do. Check out our
general guide to collimating your telescope here first before using your laser collimation tool.

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

Other issues 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.



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