How To Collimate A Telescope; Your Complete Guide to Better Focus

Using a telescope can help you see the sky clearer, look up at the stars, study the moon, and gain a greater understanding of the world around us.

With a telescope you are able to see little details that you have never noticed before, and you can learn about the planets, solar system and our universe. 

This is why keeping your telescope in good working order is so important. If you have ever gazed through your telescope and thought that the view was a little less than impressive, then it is probably time to collimate the mirrors in your telescope. 

A telltale sign that you need to collimate your telescope is if it seems a little out of focus when you are using it, and you will need to rectify the issue. Luckily, we know how!

What Is Collimation?

Collimation is the phrase that we use, which means to align the mirrors inside a telescope so that the light it collects is perfectly focused. This means that you will be able to view objects in much greater focus and detail. 

Reflector telescopes work where light is collected with the first primary mirror, which is bounced and reflected towards a secondary mirror near the opening of the telescope. This secondary mirror will then divert the light collected by the first by 90 degrees, and focus it towards an eyepiece mounted on the side of the telescope. 

For this process to work successfully, the mirrors inside of the telescope must be in a particular place. As they work to collect and reflect light amongst one another, they must be aligned perfectly for the best results. 

Over time and after many uses, the mirrors inside a reflector telescope may begin to move a little, or lose their alignment. Therefore, the process of collimation simply realigns the mirrors and returns them to the accurate position, so that you will once again be able to see the sky and any celestial objects with much greater clarity. 

This may sound like a tough process, but it is actually quite simple, and if you want to be an avid astronomer, then you will need to know how to collimate your telescope.  

Collimating A Reflector Telescope - A Step By Step Guide

Collimating a reflector telescope is quite simple, and if you follow the steps, then you will be able to do so with ease! However, there are a few things that you will need.

The first is a laser collimator, followed by a hex key (allen key) and a phillips screwdriver. You may have never heard of a laser collimator, so you can easily pick one up here

Step One

The first step is to check that the primary mirror is not gone too far out of alignment, as it may need a bigger fix than just simply collimation. 

To check this, you will want to look down the focuser without an eyepiece attached. There should be three retaining clips visible, and holding your primary mirror in place.

If you can see this, then it is fine to move onto the second step, if not then you may have to loosen the lock screw with a screwdriver.

Step Two

The next step is to ensure that the second mirror aligns with the primary mirror perfectly. To do this, you will want to use your laser collimator tool. The laser collimator tool fits in where you would normally fit an eyepiece, into the draw tube. 

You will also want to ensure that the target on your laser collimator is facing towards the back part of the telescope, and the end where the primary mirror is located. 

Step Three

Then, you must lock the collimator in place, keeping it rigid and square so that it will not sway or move once the collimation process begins. 

Step Four

Now, you can turn your laser collimator on, and look down the open aperture on your telescope.

You should be able to see a little laser dot on the mirror. You will want to adjust where that little laser dot is, and ensure that it is in the precise position in the very center of the mirror. Most telescope mirrors will have a ring marked to make this part much easier. 

Step Five

With the hex key, you will then want to adjust the screws on the secondary mirror in your telescope and move the laser. Some telescopes will require you to remove the cross-head screw for this to happen, and it can be a tricky process.

As you adjust the screws, the laser dot will move frequently, so it is best to do this slowly and carefully, keeping check of where the laser dot is. 

Step Six

When the laser dot is perfectly centered, you can tighten the locking screws back up again with your phillips screwdriver.

Step Seven

The next step is to realign your primary mirror. This can be done easily by adjusting the screws found on the bottom end of your telescope. You must also ensure that the target of your laser collimator is facing the primary mirror at this point.

This step is all about moving the laser dot to align with the center of the target, and this must be done by adjusting the screws. This point has a lot of trial and error, and you will need some patience, but most of the time you will be able to see the laser on the target with ease. 

To do this properly, you will want to loosen up the locking screws that keep the primary mirror in place. Then, you can move some of the adjusting screws to see how this affects the laser on the target. You may have to try different adjusting screws to move the laser in the right direction. 

Once the laser reaches the target’s center, you are done!

Checking Your Telescope

Collimation is a process that takes some patience and attention to detail, so do not just hope for the best. You will want to check over your telescope before using it again, to ensure that the collimation has worked properly.

This means making sure that the scope inside still has the laser dot in the center of the primary mirror, and both are perfectly aligned. Without this, you will not be able to see objects in the sky in much detail.

The laser may pop out of place when you retighten the locking screws after collimation, so you should make a little check before finishing the collimation process, as you may have to tweak it a little before using.

Your reflector telescope will most likely need frequent adjustments, and may need collimating many times if you use it extensively, so you will want to know the warning signs that your telescope needs collimating...again.

How To Tell If Your Telescope Needs Collimation

When your telescope needs collimation, you may begin to notice that something is a little off, or perhaps not the same as it usually is.

If you suspect your telescope’s collimation may have an issue, then there is an easy way to check. First, wait until the optics are cooled down, and pick a bright star in the sky. Align this bright star with the center of your eyepiece’s field of vision, and defocus it a little. 

First defocus one way, then try the other. The different defocused sides are actually called inside and outside focus. The inside focus works to the focal point inside the light cone, whereas the outside focus is the opposite. 

When testing this, if the rings are not focused, then your telescope will most likely need collimation. Keep in mind that most reflector telescopes will need collimating every time you set it up, so if something seems off, it probably is. 


If you want a quick fix, and a simple explanation of how to collimate your telescope, then here are the steps.

First, check the mirrors have a good, appropriate and approximate alignment.

Then, collimate the secondary mirror first by moving the laser dot into the center of the primary mirror.

Next, collimate the primary mirror by ensuring the laser dot centers with the collimator target. 

Finally, check over your telescope, and tweak until perfect.

You will also want to remember that you should collimate your telescope (particularly a reflector telescope) regularly. A small misalignment is easy to correct, but if it has been left for a while, and the mirrors are out of sync, then it will take you much longer to fix it! 

Andy Morgan