How to tell if telescope needs collimation before use

Sometimes the telescope can go astray. In this case, it will need collimation. In this article, we’ll show you how to set up your telescope. How to tell if telescope needs collimation?

Signs of a telescope failure

Here’s how to tell if your telescope needs collimation.

Blurred or fuzzy images

If your telescope is out of alignment, the images produced will be blurry or fuzzy, even when using the correct eyepiece.

Difficulty focusing

When the telescope is not collimated, it becomes difficult to telescope’s focuser. You may end up twisting the focus knob back and forth but not getting a clear view.

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Misalignment of the secondary mirror

If the secondary mirror is misaligned, you may notice that the image appears distorted, and may even be tilted.

Poor image contrast

If the telescope’s optics are not aligned, you may notice a loss of contrast in your images. The overall brightness and clarity may also be affected.

Double stars appear as one

If you are observing double stars, they should appear as two distinct points of light. If they appear merged or as one point of light, your telescope may need collimation.

A reflector telescope collimation

Collimating a reflector telescope involves aligning the optical components of the telescope to ensure that light passing through the lens produces a sharp, clear image. Here’s how to collimate a refractor telescope:

  1. Remove the eyepiece and any diagonal from the telescope to expose the objective lens.
  2. Look into the objective lens and center a bright object in the center of the field of view. This can be done by adjusting the telescope’s mount or by moving the object.
  3. Observe the reflection of the object in the objective lens. If it appears to be off-center or distorted, the telescope needs to be collimated.
  4. Adjust the collimation adjustment screws on the outer edge (usually located on the back of the telescope) until the image in the objective lens is centered and symmetrical.
  5. Replace the eyepiece and diagonal and test the telescope by viewing objects at different distances. If the image is still not clear, repeat the collimation process.
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Collimating a Newtonian reflector telescope

Align the mirrors: First, ensure that the primary mirror is aligned with the secondary mirror.

This involves centering the secondary mirror in the eyepiece holder on the outer edge, and then adjusting the primary mirror until its reflection is centered in the eyepiece.

Adjust the secondary mirror: If the reflection of the primary mirror is not centered on the eyepiece, you will need to adjust the secondary mirror.

To do this, loosen the screws that hold the secondary mirror in place and gently tilt it until the reflection is centered.

Fine-tuning: Once the mirrors are aligned and the reflection is centered, it’s time to fine-tune the collimation.

This involves looking through the eyepiece and adjusting the primary mirrors and the telescope’s secondary mirror until the image is crisp and clear.

Repeat as necessary: It may take a few attempts to get the collimation just right. Don’t be afraid to make multiple adjustments until the image is sharp and in focus.

Check and adjust regularly: It’s important to regularly check and adjust the collimation of your reflector, as it can become misaligned due to bumps or other disturbances.

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Adjusting the mirrors on a telescope

  1. Begin to collimate your telescope by attaching any additional eyepieces or accessories on the outer edge of your telescope.
  2. With your telescope on a stable surface, remove the dust caps from the primary mirrors and the telescope’s secondary mirror.
  3. Looking through the eyepiece, adjust the focus until the image is clear.
  4. Using a tool with collimation knobs, center your mirror by adjusting the three screws that hold it in place.
  5. Next, adjust the primary mirror by using the tool to center it.
  6. Repeat step 3 to ensure the image is still clear.
  7. Finally, adjust the angle of your finder scope to be aligned with your telescope.

Collimating with a Cheshire or collimation cap method

Collimate your telescope means aligning its mirrors or lenses to ensure sharp focus. The Cheshire collimator and collimation cap are two common tools used for correct collimation.

A Cheshire collimator is a sight tube-like instrument with a small opening at one end, through which light can pass.

It also has a small angled mirror at one end.

To use it, you insert it into the focuser of your telescope and adjust the primary mirrors and telescope’s secondary mirror so that the light passing through the collimator reflects off the angled mirror and back through the tube.

The reflected light should form a bright circle in the center of the field of view. If it doesn’t, you need to adjust the mirrors until it does.

A collimation cap is a simple device that fits over the end of the telescope tube. It has a small hole in the center, through which you can see the mirrors.

To use it, you adjust the main mirror until its reflection appears centered in the collimation cap’s hole.

Next, adjust the secondary mirror until its reflection appears centered in the hole as well.

In both cases, the goal is to get the telescope’s mirrors aligned so that light passing through the telescope is focused properly.

Practice makes perfect, so don’t worry if it takes a few tries to get it right!

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Laser collimator 

A laser collimator involves using a laser beam to align and adjust the components of an optical system, such as a telescope or camera lens, to improve the clarity and accuracy of the image produced.

The beam of the laser collimator is aimed through the system and the resulting pattern and alignment are observed to make adjustments as needed, typically using small screws or knobs to adjust the positioning of lenses or mirrors.

The laser collimator method of collimation is often preferred for its precision and ease of use, although it may not be suitable for all systems. However, laser collimators are convenient to use.

Collimating on a star test

Collimating is the process of aligning the optical tube of a telescope so that the light rays converge at the same focal point, resulting in a clear and sharp image.

To accurate collimation your telescope with a star test, you will need to follow these steps:

  1. Choose a bright, isolated star in the center of the field of view.
  2. Use a high-magnification eyepiece and focus the star as sharply as possible.
  3. Center the star in the field of view by adjusting the telescope’s mount.
  4. Look through the eyepiece and see if the star appears as a pinpoint of light. If not, this may indicate a misalignment of the optics.
  5. To adjust the collimation of the optical tube, use a tool or a collimator cap to adjust the secondary mirror holder of the primary and secondary mirrors.
  6. Turn the three adjustment screws on the primary mirror until the star appears to be a small, symmetrical dot.
  7. If necessary, use the collimator cap to adjust the secondary mirror until the star appears centered and symmetrical.
  8. Recheck the focus and alignment of the star to ensure that the collimation is correct.

Collimate your telescope on a star can be a challenging but rewarding process, as it can significantly improve the quality of your observations.

A Schmidt-Cassegrain collimating method

Proper collimation of a Schmidt-Cassegrain telescope involves aligning its optical elements to optimize the sharpness and clarity of the images it produces.

Here’s how to do it:

  1. Find a bright star in the sky and center it in the telescope’s eyepiece.
  2. Using a collimation cap or a Cheshire eyepiece, insert it into the telescope’s focuser and rotate it until it’s centered.
  3. Look into the collimation cap or the Cheshire eyepiece to see the reflection of the telescope’s primary mirror.
  4. Adjust the primary mirror’s adjustment screws of the primary mirror until its reflection is centered.
  5. Remove the collimation cap or the Cheshire eyepiece and insert a star diagonal or a regular eyepiece.
  6. Focus the telescope on the same bright star as before.
  7. Look at the star’s diffraction pattern, which should be a round and concentric set of rings.
  8. If the diffraction pattern appears skewed or asymmetrical, use the secondary mirror’s collimation screws to align it with the telescope’s optical axis.
  9. Repeat steps 6 to 8 until the star’s diffraction pattern looks perfectly round and concentric.

Collimate your telescope with a Schmidt-Cassegrain method can take several rounds of adjustments but be patient, it is essential to improve your telescope’s performance.

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Collimating a Maksutov-Cassegrain

  1. Start by setting up your telescope in a stable location that is free from vibrations and light pollution.
  2. Insert your longest focal length eyepiece into the telescope and focus on a distant object such as the moon or a star.
  3. Next, remove the eyepiece and replace it with the tool. The tool is typically a small, circular metal piece with a center hole and three or four small adjustment screws that protrude from its edges.
  4. Center the tool in the telescope tube and adjust the screws until the tool is snugly and centrally in place. You may need to rotate the tool slightly to ensure that it is perfectly centered.
  5. Look through the tool and adjust the main mirror. The primary mirror is located at the bottom of the telescope sight tube, and it will typically have screws or bolts that can be used to adjust its position.
  6. To adjust the main mirror, you’ll need to use the three or four small screws on the tool as reference points. Adjust the primary mirror screws until the reflected images of the reference screws line up with the screws themselves.
  7. Once the primary mirror is properly aligned, you can move on to aligning the secondary mirror. The secondary mirror is located at the top of the telescope tube and will typically be attached to a small metal arm.
  8. Look through the tool again and adjust the secondary mirror until the reflected images of these reference screws line up with the screws themselves.
  9. Repeat steps 6-8 until both the primary and secondary mirrors are properly aligned.
  10. Finally, remove the collimation tool and replace it with an eyepiece to verify that the image is crisp and clear.

We have more information on telescopes on our website. If you are interested not only in how to tell if telescope needs collimation, but also why it becomes blurry, please make sure to click on the link.


What are the signs of bad collimation?

Here are some signs of bad collimation:

Blurry or distorted images

Poor collimation can cause blurred or distorted images, making it difficult to see details.

Uneven brightness or illumination

If the collimation is off, the brightness or illumination across the image may be uneven.

Difficulties with focusing on

If the collimation is bad, it can cause difficulties in focusing and may require multiple attempts to get sharp focus.

Star elongation

When the collimation is not accurate, stars may appear elongated or stretched in one direction.


Coma is a type of optical aberration that causes stars to appear as a comet-shaped smear rather than a point of light. Bad collimation can cause a coma in a telescope.


Poor collimation can also cause astigmatism, which causes stars to appear as lines rather than points.

Which telescopes need collimation?

Reflecting telescopes (including Newtonian, Cassegrain, and Dobsonian telescopes) require collimation because their mirrors can become misaligned due to transportation, temperature changes, or other factors.

The Telescope’s collimation of adjusting must be the alignment of the mirrors to ensure the telescope is properly focused and provides sharp, clear images.
On the other hand, refracting telescopes (such as refractors and Schmidt-Cassegrain telescopes) do not require collimation since they use lenses instead of mirrors.

How often should you collimate a telescope?

It depends on the type of telescope and usage. In general, a telescope’s collimation should be done every time you take it out for observation, especially for reflector telescopes.

However, some users may collimate telescope less frequently if they handle them carefully, and do not experience any drifting or misalignment. It is recommended to check the collimation every few observing sessions and adjust it if necessary. If the telescope is dropped or bumped, collimation should be checked immediately.

How do I know if my refractor is out of collimation?

Here are some signs that your refractor may be out of telescope collimation:

– Blurry or hazy views.
– Difficulty focusing or achieving a sharp image.
– Distorted star shapes or asymmetrical star images.
– Uneven brightness or sharpness across the field of view.
– Double images or ghosting in the view.
– A noticeable shift in image position when moving from the center to the edge of the field of view.

More information on how to tell if telescope needs collimation you can find by following the link.


Telescope collimation doesn’t have to be an intimidating task that ruins your eagerness to use it.

This informative article shows that the process is quite simple and can be done in various ways, such as laser collimators, collimating a Maksutov-Cassegrain, and others.

Even if you own a reflector telescope that needs frequent collimation, it can be done with ease and minimal equipment.

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.

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