How to Collimate a Newtonian Reflector Telescope

Graphic of laser collimator with the text how to collimate a telescope being depicted.

Collimation determines the alignment of all components in a telescope in order to transfer light into its best focus. Newtonian Reflector Telescopes are likely to go out of alignment if they are bumped around too much or from gradual wear and tear. However, they can be re-aligned via collimation. Follow these steps on how to collimate a Newtonian Reflector telescope.

Collimating a Newtonian Reflector Telescope

Step 1. Get yourself a trusted collimator – Saxon 1.25-inch Cheshire Collimator Eyepiece

Step 2. Familiarise yourself with the with the all the components of the tube, mainly the primary mirror secondary mirror and focuser, where they are and what they do.

Step 3. First, make sure the secondary mirror is centered under the focuser. By inserting the Cheshire collimator, check if the secondary is centered. If it is not, adjust the three adjusting screws and center bolt if required until the secondary mirror appears centered and circular.

Step 4. Next you need to align the secondary mirror with the primary mirror. Using a laser collimator makes this process easier. Insert collimator into focuser and adjust the secondary with the adjustment screws until the laser beam hits on the center of the primary whilst double checking everything is still centered.

Graphic showing secondary mirror is out of alignment with primary as depicted on the laser collimator and reflector mirror.
Here the collimator indicates the secondary is out of alignment with the primary.

*Repeat steps 4 and 5 as necessary making sure all elements are still centered

Step 5. Remove laser collimator briefly and look to see whether the primary is centered in the reflections. If not, adjust the appropriate rear screws of the primary to center it as seen in the diagonal. Then insert the laser collimator and check that it’s still centered in the primary.

Then remove laser collimator and adjust the primary to see if it’s reflected in the diagonal. Repeat these steps until the laser is in the center of the mirror and the primary is centered in the diagonal.

Graphic depicting secondary mirror screws being adjusted to center it with the primary as seen with the laser dot being centered on the primary
Use an Allen key to adjust the screws of the secondary and align it with the primary. This is done when the laser dot is in the center of the primary.

Step 6. Most importantly you need to adjust the primary mirror. While the laser beam is on the center of the mirror, use the three screws at the back of the mirror cell to adjust the primary so that the beam returns to where it is being emitted from.

Graphic depicting screws of the primary being adjusted to center the mirror.

Step 7. Test to see if the telescope is aligned.

Final Comments

Collimating your telescope is not as complex as it seems. With a bit of trial and error, you won’t have any trouble collimating. Following these steps will make you more confident in knowing how to collimate a Newtonian Reflector telescope. However, there instances where collimation may be too convoluted depending on the unalignment of the mirrors. Likewise, Cassegrain telescopes are far more complicated to collimate compared to reflectors. But not to worry! At Optics Central, our Service Technician would happily collimate those telescopes for you.  

Leave a Reply

Your email address will not be published. Required fields are marked *