Tag Archives: camera phone

Collimate a Telescope without a Cheshire

In this video, I demonstrate how I collimate my newtonian telescope without a cheshire (if you don’t have one). There are 3 basic steps to collimating: 1) Center the secondary under the focuser; 2) Align the secondary to the primary; 3) Align the primary back to the secondary. In step one, I will use a camera phone instead of a cheshire to center the secondary under the focuser tube. Click on the video below to play.

How to Centre the Secondary Mirror by Using a Camera Phone

Today, I learned a lesson in troubleshooting a collimation problem with my new dobsonian telescope. When I took the secondary mirror off to install a washer, I could not properly get it collimated with my laser collimator on reassembly. One problem with laser collimators is that it assumes that the secondary mirror is already centred under the focuser. But that is easier said than done. Until now.

Reflection of the primary mirror’s clips are off centre.

Symptom: When I looked through the collimating cap after a laser collimation, it looked like the above photo. The primary mirror’s clips were off-centre. It was actually worse than what the photo shows. However, the photo provides a clue of what the problem may be: the secondary is not centred.

So below were the steps I took to collimate after disassembling the secondary:

Reflection of the primary tube with the cover on.

Step 1: Above, I rough aligned the secondary under the focuser and took a photo. To the untrained eye (like mine), my secondary mirror looked centred through the 1 mm hole of my collimating cap.

Using a ruler to measure the secondary mirror’s distance from the focuser tube.

Step 2: That was until I took a ruler and measured it on my screen as shown above. So I kept adjusting the secondary until both sides were equal. I pinched to zoom for more accuracy.

My refractor’s diagonal being used as a collimator.

Step 3: I used a right-angle diagonal focuser above from my refractor so that I can adjust the primary adjustment screws and receive instant feedback without walking back and fourth. I centred the donut to the reflection of the secondary.

The reflection of the primary mirror clips appearing centred.

Step 4: I replaced the collimating cap to verify alignment and it looked good as shown above. I then followed it up with a laser collimation and it still looked good afterwards.

Out in the field, I will be star testing it for fine tuning. My laser collimator was 99% true so if you plan on doing the same procedure above, check to make sure your laser collimator is properly collimated in the first place. Credits go out to the following AstronomyForum.net members for helping me troubleshoot the problem: mlk1950, CamelHat, andrejl2, Jason_D