How to collimate a telescope: a complete guide

Collimation is a crucial operation for all telescopes to ensure that the light traveling through the system is properly focused and centered, and it is especially important for a reflector telescope. Images may appear blurry, out of focus, and lack contrast, and detail when improper collimation is used.

However, it may be time to collimate your telescope if your nighttime sky views have diminished or if you are having trouble getting your telescope to focus.

In this article, we will go over how to collimate a telescope, as well as the equipment and methods needed to do so.

how to collimate a telescope
Image credit:

Understanding how to collimate your telescope is a crucial skill that will enable you to get the most out of your observation sessions and capture breathtaking views of the night sky, regardless of whether you are a beginner or a seasoned professional. I hope this guide will be interesting and informative for you to read.

Factors to take into account before collimating a telescope

A successful collimation process depends on several factors that should be taken into account when collimating a telescope.

collimate a telescope 10
Image credit:

The following are some important things to bear in mind:

Type of the telescope. The collimation procedure can vary based on the type and design of the telescope, so it’s critical to choose the best technique for your particular telescope. If you are doubtful, refer to the instruction booklet or ask a skilled astronomer or telescope technician for assistance.

Condition of the telescope. Before collimating your telescope, check to see that it is in good shape and free of any damage or flaws that can interfere with the collimation procedure. Check the primary mirror and the secondary mirror, lenses, and other optical components for dust or other debris that can affect the collimation.

Time of day. Because it can be more challenging to view the optical components in low light, it is recommended to collimate your telescope during the day or in the early evening while there is still some daylight.

Weather. The weather can also have an impact on the collimation process, especially if it is windy or cloudy as this can cause the telescope to move or vibrate, making proper collimation more challenging.

Before collimating, it is crucial to ensure that the telescope is perfectly aligned and stable because any movement or vibration can interfere with the collimation procedure.

Patience and practice are essential when collimating a telescope because it can be a difficult operation, especially for novices. Don’t give up if accurate collimation doesn’t work perfectly the first time; it can take numerous tries.

collimate a telescope 3
Image credit:

Collimation of Newtonian reflector telescope

Despite the reflector telescope’s appearance of complexity, it has three optical components: the main mirror (commonly referred to as the “primary mirror”), a small, flat mirror towards the top of the sight tube (known as the “diagonal” or “secondary mirror”), and the magnifying eyepiece you use to view the object.

The secondary mirror, which is positioned on the front of the telescope optical tube, must first be found. You’ll notice that it is held in place by something, like a glass pane. Additionally, it has adjustable collimation screws.

Once they are correctly positioned, gently tighten or loosen the secondary mirror holder where the three adjustment screws are located without touching the secondary mirror. The circles in the diffraction pattern will be able to move a little as a result, becoming more concentric. It feels like you are softly pulling and pressing them.

While doing this, you must make sure that the pattern is visible to you. Use a device that connects to your Newtonian reflector telescope to get a clear view of the image, or get assistance from a friend.

In addition, place the telescope on a flat surface, and instead of pulling on all the locking screws at once, which can be confusing, you should focus on just one when you first begin to pull on the locking screws.

Because even the smallest adjustment screws will affect the primary mirror and the secondary mirror of the telescope, you must move with great caution and precision.

To avoid further confusion, pay close attention to which screw you moved, how much you moved it, and in which direction.

You must return the screw to its original point and try moving it in the opposite direction to see if that improves the situation after you notice that the diffraction pattern is becoming further out of focus. Alternatively, use a different screw. On the other side, if the circles appear to be improving, keep adjusting the same screw.

collimate a telescope 4
Image credit:

The procedure of collimating a telescope

Depending on the type and design of the telescope, the procedure of collimating a telescope can vary, but the fundamental steps are as follows:

Consult your telescope’s instruction handbook. It’s crucial to read your telescope’s instruction manual before you start collimating it. You may find detailed instructions on collimating your telescope in the manual, along with a list of any specialized equipment or methods needed.

collimate a telescope 5
Image credit:

Pick a collimation tool. Various collimation tools are available, including a collimation cap, a laser collimator, and a star test.

To align the mirrors, a laser collimator beam of light is directed through the telescope. During a star test, the optical components are aligned using a bright star as a reference point.

Adjust the secondary mirror. A reflector telescope secondary mirror must be adjusted to ensure that it is properly positioned about the telescope’s primary mirror. Adjust the location of the secondary mirror until the primary mirror reflection is centered using a collimation cap or laser beam collimator.

To Adjust the primary mirror, turn the collimation knobs (which are on the rear of the scope) until you can see the dot in the center of the primary mirror.

Adjust the tilt until the outer edge of the primary mirror is perfectly aligned with the outer edge of the secondary mirror.

Perform a star test. Perform it to make sure the telescope is appropriately collimated after you have adjusted the primary and secondary mirrors. Use an effective collimating eyepiece to magnify a bright star so you can see it as an individual ray of light. You might need to make more modifications if the star appears deformed or has a “tail.”

Repetition is key. If you have a reflecting telescope, collimation should be done frequently. It is ideal to collimate your telescope each time you go out for observation or at least once a month.

 Collimating a telescope can be a difficult task, but with practice and the correct equipment, it can become a normal aspect of keeping your telescope’s performance. It is always preferable to refer to the instruction manual or ask a skilled astronomer or telescope technician for guidance if you are unsure how to collimate your telescope.

collimate a telescope 6
Image credit:

Equipment needed to collimate a telescope

Depending on the type and construction of the telescope, several tools may be required to collimate it, however, the following are some of the most frequently employed ones:

Collimation cap. It is a straightforward device that fits over the eyepiece holder of a reflecting telescope and aids in adjusting the secondary mirror holder.

Laser collimators. To align the mirrors of the telescope, a laser collimator beam of light is directed through the instrument.

It is a more sophisticated tool that can assist you in achieving more collimation precision.

Cheshire eyepiece. In a reflecting telescope, a Cheshire eyepiece is a specialized collimation sight tube equipment that enables you to see the primary mirror’s light reflection in the telescope’s secondary mirror.

Barlow lens. By enlarging the image with the use of a cap or laser collimator, a Barlow lens makes it simpler to notice the details that need to be adjusted.

A star chart or planetarium software. You’ll need a bright star to use as a reference point when using a star chart or planetarium software to conduct a star test. Based on your location and the time of night, a star chart or planetarium software can assist you in choosing a suitable star.

Wrenches and screwdrivers. They may be required to remove or tighten nuts or locking screws that are used to modify the position of the secondary and primary mirrors.

collimate a telescope 7
Image credit:


Better image quality. Collimation aids in ensuring that light entering the telescope through the primary mirror is properly focused and centered, producing images of celestial objects that are sharper, clearer, and more detailed in the focal plane.

Better contrast. The perfectly collimated scope can also improve the contrast of the images, making it simpler to see minute details and features.

A telescope’s tracking precision can be increased through collimation, making it simpler to follow celestial objects as they move across the sky.

Longer lifespan. By preventing damage to the optical components and guaranteeing their alignment, regular collimation can help your telescope last longer.

collimate a telescope 8
Image credit:


Complexity. Collimating a telescope may be a challenging and time-consuming task, especially for novices or those with little experience.

Collimating a telescope requires specialist equipment, such as collimation caps or laser collimation equipment, which can be pricey and occasionally hard to find.

Risk. Collimating a telescope improperly runs the risk of damaging the optical components, which are expensive to repair or replace.

Regular maintenance. It is required, especially for reflecting telescopes, where collimation can be a time-consuming and continuing operation.

The perfectly collimated scope can considerably enhance image quality and increase the lifespan of the instrument, thus overall, the benefits outweigh the drawbacks.

But if you are unclear about the procedure, you should proceed with caution and seek guidance from an experienced astronomer or telescope technician.

collimate a telescope 9
Image credit:


Is it easy to collimate a telescope?

Collimating a telescope can be an easy task or it can be difficult depending on the kind of telescope and the level of precision needed. The act of collimating a telescope involves lining up its optical components so that light traveling through it is appropriately focused and centered.

Because their mirrors can move out of alignment owing to vibrations or other environmental reasons, the reflector telescope like Newtonian and Cassegrain often require more frequent collimation than refractor telescopes.

To collimate a telescope, the secondary mirror or lenses of a reflector telescope or a refractor telescope are normally moved into alignment with the primary mirror or lens. This can be accomplished either by using a star as a reference point or by using specialist equipment like a collimation cap or a laser collimator.

Even though collimating a telescope can initially be intimidating, with practice and the correct equipment, it can become an everyday aspect of keeping your telescope in top performance.

How do I know if my telescope needs collimation?

There are a few symptoms that your telescope may require collimation:
Blurry images. If the images you are viewing through your telescope appear blurred or out of focus, it may be an indication that the optical elements are not properly aligned.

Poor contrast or detail. If the contrast in your photos seems poor or you have problems seeing small details, the telescope may not be properly collimated.
Images of stars are distorted. Stars should appear as sharp points of light when observed. The telescope is not adequately collimated if they appear deformed, with a “tail” or a “comet” shape.

Uneven illumination. It may be an indicator that the telescope is not properly collimated if the image in your telescope appears brighter on one side than the other or if there is a “hotspot” or “shadow” in the middle of the image.

It is a good idea to check your telescope’s collimation if you see any of these symptoms. You may get the best possible views of the night sky by routinely testing and maintaining the collimation of your telescope.

What happens if your telescope is not collimated?

Without collimation, your telescope’s views may appear blurred, have low contrast, and the stars can appear disordered, or have uneven illumination.

Where is the primary mirror of the telescope located?

The position of the primary mirror is determined by the telescope’s kind and design. The primary mirror, on the other hand, is typically found near the back of reflecting telescopes, at the bottom of the tube.


Collimating a telescope is an essential maintenance procedure that will assist guarantee that you are receiving the greatest possible views of the night sky. Although collimation can first be difficult, it can eventually become a routine aspect of keeping your telescope performing well.

To collimate a telescope, the optical elements must be moved into the correct alignment. This can be accomplished either by using a star as a reference point or by employing specialist equipment like a collimation cap or a laser collimator.

In addition, the collimation of your telescope needs to be checked and maintained frequently, especially if it is a reflecting telescope that is blurry or out of focus, lacks contrast or detail, star images are distorted, or has uneven illumination. Then the telescope may need collimation.

You can make the most of your telescope and ensure that you are receiving one of the best views of the night sky by learning how to collimate your telescope and including it in your regular maintenance schedule.

Ida Stewart

I have had the incredible opportunity to work as a tour guide at the planetarium for over 5 years. Ever since I was a child, astronomy has held a special place in my heart, and I have nurtured a deep passion for exploring the wonders of the universe. Among all the celestial bodies, Mars has always fascinated me the most, captivating my imagination with its mysterious allure.

Leave a Comment