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Nothing is more desirable for a sky-lover or a beginner astronomer than to observe the night sky with his Dobsonian telescope. Just imagine you have your very own Dobsonian telescope in hand; you have spent a good time assembling it and waiting for the night. When the moment you cherish has come, you are excited to have a glance at the universe. You have placed your eye in the eyepiece. And then you realize something has happened to your reflector. You are not getting a clear image. The moon is not showing up. The Saturn is looking like a teacup with a double handle. No, there is no problem with your telescope. All you need is to pamper your telescope. It is high time you should collimate your Dobsonian telescope. 

In this article, we will be telling you how to collimate a Dobsonian telescope. This is a must-skill for beginner astronomers. Also, you can check our article How to use a Dobsonian telescope if you are a newcomer. 

What Is Collimation?

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Collimation is a process used to align all the telescope components to bring light to its best focus. All types of telescopes, especially reflectors, need to go under this process frequently. There are two types of collimation- optical collimation and mechanical collimation. 

Optical collimation is a process where a telescope’s optical components are aligned to bring the correct orientation of an image in the telescope’s focal plane. On the other hand, mechanical collimation means the alignment of the physical components of a telescope.

The mechanical collimation is not that tough to do. It depends on how correctly you assemble the telescope. But optical collimation is not that easy. It takes a good time to master the skill of optical collimation. In this article, we will be talking about optical collimation. 


How Can You Collimate a Telescope? 

There are few ways to collimate a telescope. But the most effective way is to collimate a telescope is by using a collimation cap. Also, you can go through the process of laser collimation. A laser collimator is used in this method. Some astronomers prefer the Cheshire collimator to collimate their telescope. 

Equipment You Need to Collimate a Dobsonian Telescope

Collimation cap

Collimation cap

A collimation cap is a tube or plug that fits in the focuser of the reflector telescope. It has a hole in the dead center. This dummy eyepiece helps you to align the mirrors of the Dobsonian telescope. You can buy a collimation cap from any online store at a meager price. You can make your very own DIY collimation cap.

Laser collimator

Laser collimator

A laser collimator is a device or gadget that emits a laser beam. The device sits in the focuser and shines a laser beam that reflects perfectly onto the hole where it came from. It is effortless to collimate a Dobsonian with a laser collimator. But it has some demerits too. Sometimes the commotion may go wrong with a laser collimator.



A Cheshire collimator is like an eyepiece that aligns the optical axes of a Dobsonian telescope’s mirrors or lenses. Like other collimation tools, you need to put it in the focuser to collimate the telescope optically.  

After researching a lot, our expert team has concluded that the best way to collimate a Dobsonian telescope is to collimate it with a collation cap. Because using the Cheshire is quite tricky and laser collimator does not give you the perfect result every time. So, learn the use of a collimation cap to collimate a Dobsonian telescope in easy steps. 

Steps To Collimate A Dobsonian Telescope With A Collimation Cap

Collimate A Dobsonian Telescope With a Collimation Cap

primary mirror nor secondary is correctly positioned

In this illustration, neither the primary mirror nor secondary is correctly positioned.

primary mirror nor secondary is correctly positioned

In this picture, the primary mirror and the secondary are correctly positioned.

dobsonian collimation

The secondary mirror’s tilt is adjusted with the three small, recessed screws threaded into the spider hub.

  1. First of all, you need to confirm the fact that your telescope needs collimation. Now for this purpose, you can use the ‘out-of-focus star method.’ If you see that the airy disc is off-centered, it means your Dobsonian needs collimation. 
  2. Carefully take note of the side closest to this center circle of light because you need to adjust the mirrors on that side. 
  3. Now get your collimation cap. You can use a store-bought cap or a DIY collimation cap. 
  4. It is time to take off the large lens cap of the telescope. Be very careful in this step. 
  5. Place the collimation cap in the focuser. Look through the focuser for the three clips of the larger primary mirror at the back.
  6. Alter the adjustment of the screws on top of the mirror holder until you see the three clips. 
  7. Now check the primary mirror at the back. Adjust the three screws at the base of the telescope. 
  8. Your collimation process is complete. Use the ‘out-of-focus star method’ again to make it clear that your collimation process is perfect. 
  9. If the result is still the same, repeat the steps to do the collimation correctly.

We suggest you watch this video on Collimating a Dobsonian telescope.

Frequently Asked Questions

How Do You Know If You Need to Collimate Your Telescope?

When you focus on a very bright star, but instead of a clear image, all you can get is blurriness. You may see a diffraction pattern around it. This is the time when you need to collimate your telescope. For a specific result, you are suggested to use the ‘out-of-focus star method.’  

Why Do You Need to Collimate a Telescope?

If your telescope is not aligned correctly or collimated, you will not get a clear view of the night sky. You won’t be able to see the stars or the planets. And this is a thing that you do not want as an astronomer. So, to get a perfect view of the universe, you need to collimate your telescope when necessary. 

How Often Do You Need to Collimate a Telescope?

This matter depends on the usage of the telescope. If you are using the telescope roughly daily, you may need to collimate the dob frequently. Sometimes the transport of the telescope unsettles the alignment of the telescope. So you might need to collimate your telescope after a ride with it. 


Collimating a Dobsonian telescope is a fundamental process if you want to get a clear view of the asteroids, stars, planets, and nebulae. If you follow the steps correctly, you will be able to align your telescope easily. Still, let us know if you wish to know anything else. Leave your query in the comment section. Our expert team will answer your questions as soon as possible.