How To Collimate Mirrors On Newtonian Reflector

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Collimation is the alignment of the telescope optics. It means you have to adjust both primary and secondary mirror to get the best image possible. For some people, collimation is a nightmare and many times they buy refractor instead of a reflector because of that. But, it is a very simple process, and you don’t have to be scared of it. Most people think that collimation is a long, frustrating process and that you need expensive tools to do that.

I’m going to show here how to collimate your reflector for free without the collimation tools. Just take it easy, it’s not rocket science, and you will get crisp image after that. There are two types of collimation. One can be done without the tool and the other one when you are using a collimator tool. You may think that the collimation with the tool is better, but that is not true.

Both methods can be accurate and sometimes the way without the tool is better. I will explain why is it better at the end of this article. The technique I will show you here applies to all reflecting telescopes. Now, before we start, I have to mention two safety precautions.

If you are doing the collimation of the telescope, always move it to a horizontal position. Never do anything around the front opening if you don’t have a scope in a horizontal position. You are risking to drop something in the tube, and it can slide down on your primary mirror. If something falls on the primary mirror, it can destroy it! So, be careful with that and don’t make this mistake.

The second warning is not to point the telescope towards the sun- ever! When doing the collimation, try to do it inside your house. I’m always doing my collimation inside, and you should be too. But, if you really want to do it outdoors, be very careful.

Collimating Newtonian Reflector Without The Tool

I myself use this method, and I love it. It’s free, and it takes a few minutes before the observing session. It is done visually. I will break it down into steps so that you can follow them with me.
Beforehand, we need to prepare one Philips head screwdriver and small hex key. This may differ with different telescopes. And we need one collimation cap. It will help you center your eye around the focuser. The last thing we need is a sheet of white paper.

The only special tool is the collimation cap which is a standard cap with the hole in the middle and reflection surface inside. It is for centering the donut on the primary mirror which I explain later. You can buy one, or you can make one like me from the old cap of the old telescope. You have to make a hole in the middle and put a piece of aluminum foil inside so it can reflect light.

Aligning The Secondary Mirror

Always start the collimation by aligning the secondary mirror first. Remove the dust cap from the telescope and the cap on the focuser. Now, place the white sheet of paper inside the tube opposite to the focuser under the secondary mirror. Be careful not to touch the reflective surface of the secondary mirror. This will help you to align the secondary mirror better because it will provide a bright background. The mirror will stand out while you are looking through the focuser.

Put the collimation cap that we prepared in the focuser and look through the hole. You will see a few reflections, and they may not be centered, but it doesn’t matter yet because we are doing only the secondary mirror alignment. We need to check where is the mirror located in relation to the focuser. Many telescopes have factory aligned secondary mirrors, so maybe you won’t have to do anything with that now. You have to see even space around the secondary mirror through the cap hole in the focuser.

If it’s not aligned and it is closer to the primary mirror or the front of the telescope, you need to make adjustments to center it. Take the hex key and the Phillips head screwdriver. On the mount of the secondary mirror, you have 4 screws. One in the middle that is moving the mirror in and out of the scope. The rest of the socket head screws are for adjusting the tilt of the mirror. To move the secondary mirror, you have to loosen three socket head screws around the middle screw by one or two turns. Then, take the Philips head screwdriver, hold the base of the secondary mirror with your second hand and turn the middle screw counterclockwise to push the mirror towards the primary mirror or clockwise to move it towards the front of the tube. While doing that, keep looking through the cap hole in the focuser. It will allow you to center the secondary mirror. Make sure that the secondary mirror doesn’t rotate out of the position while you are centering it. Also, remember to keep the telescope in the horizontal position so if you drop something to the tube, it will not slide down on the primary mirror.

The last step in aligning the secondary mirror is to adjust its tilt. It means that you have to see the reflection of the primary mirror on the secondary mirror perfectly centered. To do that you need to play with the three socket head screws around the center screw. You don’t have to make these adjustments very often in the future, so make sure you do a good job here. When you are done with the secondary mirror, remove the white sheet of paper carefully out of the tube and don’t touch the reflection side of the mirror. Now we can move on the primary mirror.

Aligning The Primary Mirror

If you are collimating the primary mirror, you have to check that it has a small donut in the center. All reflecting telescopes should have that, but some cheap starter scopes can have a mirror without the donut. It is very hard to do collimation without that. We have to align the donut circle with the dot which is the reflection of the collimation cap hole in the secondary mirror.

To do so, we need to work with the collimation knobs on the primary mirror at the back of the telescope. Most telescopes have easy to use knobs and some standard screws. There is a set of 6 knobs. 3 knobs are adjusting the tilt of the primary mirror, and 3 of them are just locking knobs that lock the mirror in the position you set. First, we have to loosen the locking knobs. Then look through the hole in the cap and adjust the other knobs until the donut circle is centered in around the center dot. It will make a bull eye.

Some telescopes are long, and you won’t be able to reach the collimation knobs on the primary mirror. You can overcome this by adjusting it with slight movements and then checking it in the focuser to work your way to the bull eye. Or you can ask your buddy to help you by looking in the collimation cap while you adjust the primary mirror. When you finish, tighten the locking screws. And we are done! The collimation of your reflector is perfect.

Collimation Of The Reflector With a Collimation Laser

You can also buy laser collimator to collimate your telescope. But the issue I have with these tools is that it will give you more problems. The first thing is that those tools wobble in the eyepiece holder, so collimation might not be accurate with them. Another thing with lasers is that the laser must be collimated as well before performing any collimation with the telescope. You would be surprised how many lasers come not aligned. If you have one, you can check it for yourself. Just put the laser in the focuser, look inside the tube and start to rotate the laser. If the red dot stays in one place during rotation, everything is ok. But if it begins to circle on the mirror, then you have a problem, and you have to collimate the laser. I think that the method without the tool that I have shown you is much easier and more accurate collimation of the Newtonian reflector.


No matter what method you choose, whether one with or without the tool, remember that the collimation is important like changing the oil in your car. I’m doing it always before the observing session to make sure that the mirrors of the telescope are in perfect alignment. It is a big difference looking through the Newtonian telescope that is properly collimated. The image is crystal clear, and you can enjoy the view of the objects. I wish you clear skies everyone and see you in the next article.

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