Are you having difficulties capturing a clear, focused image with your new or first telescope? Have you noticed double images or stars that aren’t so concentric?
If so, you’re probably wondering how to tell if telescope needs collimation.
For the amateur astronomer, trying and capturing the perfect image on a new telescope can be frustrating.
Having issues with double images and poor focus makes it feel like you’re doing something wrong.
While there could be other issues with your telescope causing the image issues, properly collimating (aligning) your Newtonian telescope can often be an easy fix.
You can be back in the field after a proper adjustment, looking up at a crystal-clear sky through your scope.
But what are the signs that your telescope might need to be collimated?
And how can you go about collimating your telescope yourself?
This guide will break it down with step-by-step instructions to achieve optimal collimation.
You can perform a simple star test to determine if your telescope requires collimation.
You’ll focus on a bright star in the center of the field of view of your telescope.
If the image does not produce concentric circles when unfocused, your telescope is experiencing a telescope collimation issue.
You can adjust your telescope in many ways. The top methods either use a collimation cap, a Cheshire eyepiece, or a laser collimator. All three of these methods use tools to adjust the primary and secondary mirrors on reflector telescopes, bringing the mirrors back into alignment.
In this article, you get
A description of the collimation errors in reflector telescopes
A test you can use for errors
An easy guide on 3 different ways to achieve good collimation
By the end of this article, you’ll know how to tell if your telescope needs collimation and all the steps for how to collimate a telescope.
Let’s dive right in.
WHAT IS COLLIMATION IN TELESCOPES?
First things first, you probably want to know, “What is Telescope Collimation?”
The collimation process is when a telescope user aligns the mirrors inside of a telescope to create an image that is in focus and accurate. It’s a nice bit of cool science and optics to get mirrors in the correct placements to focus collected light and properly create an image.
The inside of your telescope has mirrors that bounce around the light to reflect images to you, the observer.
If you’re brand new to telescopes, read my articles Why is my telescope upside down?, How to Clean Telescope Mirror: 11-Step Guide. If you’re new to telescope mounts, read my articles Types of Telescope Mounts and Equatorial Telescope Mount vs AltAzimuth.
Light reflects off the main mirror towards a secondary mirror near the telescope’s opening. This secondary mirror sends the captured light rays to the eyepiece, allowing you to see the image.
If these mirrors are improperly aligned, the captured image will lose its focus and accuracy, compromising your image quality and producing out-of-focus star images.
That’s when you, the viewer, notice that you can’t see images that aren’t double-visions or have issues with blurriness.
The good news is that there are ways to adjust a poorly collimated telescope. Doing this will get your telescope back to its best performance standards, producing the best images possible.
The goal of collimation is the make sure the eyepiece you look through aims appropriately at the center of the primary mirror.
Collimating the telescope is where you will adjust the mirrors to their proper placements, providing crystal-clear images.
HOW DO I KNOW IF MY TELESCOPE NEEDS COLLIMATION?
As I’ve touched on above, the typical sign that your telescope needs to be collimated is the persistence of blurry and double images.
Here, I’ll explain the best way to check for collimation errors.
The easiest way is to perform something called the star test that you can do to see if your telescope needs to be collimated.
To try this test, you’ll need to use your telescope at night and try to look at a bright star in the sky.
In this description, I’ll describe how to perform star testing while trying to look at the star Sirius.
HOW TO TEST YOUR TELESCOPE FOR COLLIMATION ISSUES: COLLIMATING ON A STAR
STEP 1: FOCUS ON A STAR
First, identify a bright star in the sky, like Sirius, with your telescope.
STEP 2: CENTER IMAGE
Next, try your best to center Sirius in the telescope’s field of view, zooming in and getting it in perfect focus. Or at least, as perfect as you can get it!
STEP 3: DEFOCUS THE IMAGE
Once the star is as centered and focused as you can get it, try to defocus your image of the star.
STEP 4: LOOK FOR CONCENTRIC CIRCLES
As you are defocusing the star’s image, you’ll want to see if you can notice any concentric circles in the image.
If the circles around your star don’t look concentric, it’s a clear sign your telescope’s optics need to be collimated.
If you’re going to perform this test, I have a few tips you should keep in mind:
CLEAR SKIES NEEDED
It’s best to do this test on a night with clear skies, as any fog or haziness can impact the image and not give you an accurate read on the test. Good seeing conditions are a necessity!
USE A PROPER EYEPIECE
The test will require you to zoom in using a proper eyepiece and focus on a star. Try to use an eyepiece where the magnification results in 200x or higher.
REMEMBER THE TEMPERATURE
This tip is especially relevant for beginners! Suppose you notice any bleeding edges or fuzziness around the star. In that case, your telescope needs to acclimatize.
Ambient temperature can impact how well a telescope works. Be sure to account for any dramatic temperature changes when testing your telescope’s collimation.
HOW OFTEN SHOULD YOU COLLIMATE A TELESCOPE?
It depends on several factors, including how often you use your telescope, how well you treat it, and the environment in which you keep it.
However, as a general rule of thumb, it is an excellent idea to collimate your telescope at least once a month, assuming you use it regularly.
Constant movement can cause the alignment to shift slightly. Similarly, suppose you live in an area with high humidity or temperature fluctuations. In that case, these can also affect the alignment of your optics.
Take good care of your telescope and store it in a stable environment. You can get away with collimating it less often. Some people find that they only need to collimate their telescope once every few months or even once a year.
Ultimately, it is up to you to decide how often to collimate your telescope based on your circumstances.
However, err on caution and collimate more frequently rather than less to ensure that your optics are always in peak condition.
HOW IMPORTANT IS IT TO COLLIMATE A TELESCOPE?
It is vital to collimate a telescope because it helps ensure that the mirrors point in the right direction and that the image is in focus.
Without proper collimation, a telescope can produce blurry or distorted images.
HOW TO COLLIMATE TELESCOPE
Now that you’ve determined your telescope is experiencing a collimation issue, it’s time to begin to address how to collimate a reflector telescope by getting it aligned.
There are multiple ways you can achieve correct collimation. It’s as easy as identifying the right tool for the job that will improve the performance of your telescope. The right tool will depend on several factors, including your skill level and the exact type of telescope you’re adjusting.
We know there are many types of telescopes. Still, here, I’ll outline how to make adjustments to a reflecting telescope / Newtonian telescope.
These three methods can help you achieve excellent collimation, providing a simple solution to the problem.
THE COLLIMATION CAP METHOD
The most common way to fix a telescope’s collimation is by using a collimating cap called a sight tube. Some try making a DIY collimation cap, but it’s not worth the hassle.
These look similar to a bottle cap, with a dark exterior and a circular interior covered in a reflective material, with a small hole drilled in the middle.
A sight tube is a small collimation tool that you use to check the alignment of your telescope mirrors. Here’s how to do it:
STEP 1: PLACE CAP ON FOCUSER
First, you’ll want to place the collimation cap on top of your telescope’s focuser to check the alignment of the primary mirror.
If all is aligned, the hole in the middle of your focuser should center with the middle circle. You must correct your primary mirror placement if these don’t line up.
STEP 2: ADJUST THE COLLIMATION OF THE PRIMARY MIRROR
Now that you’ve determined the primary mirror is off, it’s time to adjust it. To do this, you must turn the collimation knobs at the back end of your telescope.
Make small adjustments until the dot from the collimation cap centers on the primary mirror.
STEP 3: ADJUST THE COLLIMATION OF THE SECONDARY MIRROR
Once you have adjusted this, you must ensure everything aligns with the secondary mirror.
This time, you’re going to look inside your collimation cap and at the outer circumference of your telescope’s primary mirror. Also, pay attention to the outside edge of the secondary mirror.
There are many ways to adjust the secondary mirror, changing its length inside the telescope tube, tilt, and rotation in relation to the telescope’s focuser.
STEP 3A: ADJUSTING THE MIRROR PLACEMENT
First, use any tool you prefer to measure the distance between the top of your telescope tube and the focuser.
Then, check the distance from the telescope’s top to the center of the secondary mirror. These numbers should be the same.
If not, adjust the focal length of the secondary mirrors inside the tube by unscrewing the collimation screws that hold the mirror in place and making the adjustment.
STEP 3B: ADJUSTING THE TILT OF THE MIRROR
The final step is adjusting the tilt of the primary mirror to help ensure the outer edge of both your primary and secondary mirrors are concentric. You’re adjusting the screws again here.
Once the primary mirror’s edge nearly touches the secondary mirror’s outer edge, you should be good.
THE LASER COLLIMATOR METHOD
A laser collimator is a great way to achieve good alignment.
In this test, you’ll leverage the use of a laser to shine a light beam through a telescope’s focuser to determine if the light is hitting your mirrors appropriately.
Here’s how to use the laser collimator:
STEP 1: READY YOUR LASER
You first need to place your laser collimator inside the eyepiece holder on your telescope, keeping it pointed to the back of your telescope. Aim it towards a wall, and turn it on. When you do this, no red dot should appear on the wall.
This step is super important, as it will determine if the optical tube is eye safe once the laser shines through. If you see the laser beam on the wall, your collimation is severely off, and you shouldn’t look through. If you don’t, you can look into the optical tube to make your adjustments.
STEP 2: ADJUST THE SECONDARY MIRROR
Now, it’s time to use an Allen wrench to adjust your telescope’s secondary mirror.
Look inside your telescope’s optical tube, and see where your laser is hitting the mirror in relation to the center dot, which is a reflection from your primary mirror.
You want to loosen and tighten your telescope adjustments screw, changing the direction of the secondary mirror. You want to adjust until the laser beam shines inside the small center dot reflected from the primary mirror.
Be careful as you do this, as tightening your screws too tight could cause damage to your telescope’s secondary mirror holder.
STEP 3: ADJUST THE PRIMARY MIRROR
Once the laser aligns with that second dot, you’ll also want to adjust the primary mirror on the back of the telescope if needed.
Turn your knobs until the laser shines to the center of that dot.
Once complete, your telescope should be appropriately aligned!
THE CHESHIRE EYEPIECE METHOD
Another handy gear you can use to fix a telescope is a Cheshire eyepiece, also referred to as a Cheshire tube. It allows for an easy and accurate collimation. Here’s how:
STEP 1: PLACE THE EYEPIECE
To begin, you’re going to put the Cheshire eyepiece inside your telescope’s focuser.
While you do this, look for the reflection of its face inside your primary mirror.
STEP 2: MAKE ADJUSTMENTS
Now, it’s time to align.
You’ll play with the three adjustment screws on your telescope, slowly moving the mirror and making minor adjustments until the reflection from the eyepiece is centered.
STEP 3: GET THINGS ALIGNED
This process is slow and steady and could take users a long time as they play with their adjustment screws and knobs to achieve proper telescope collimation.
But with time, you should get things aligned!
Every telescope will eventually need collimation, but it can be challenging to tell when your instrument needs adjustment.
With some practice, you should keep your telescope in tip-top shape and enjoy many nights of clear views.
This article has given you a few things to look for the next time you’re out under the stars.
If you still have questions, please comment below, and I’ll do my best to provide a detailed response.
Thanks for reading!
FREQUENTLY ASKED QUESTIONS
HOW ACCURATE DOES COLLIMATION NEED TO BE?
There is no definitive answer to this question since it depends on factors such as the quality of your optics, the seeing conditions, and how critical you are of the image quality. However, a general rule of thumb is that your collimation should be within 1/8th of an inch for a Newtonian reflector telescope and 1/4th for a Schmidt-Cassegrain telescope.
ARE LASER COLLIMATORS WORTH IT?
Yes, laser collimators are worth it. If your telescope is out of collimation, it will likely not perform as well as it could. Many amateur astronomers use laser collimators to help keep their telescopes in alignment. Laser collimators are relatively simple to use and can be very helpful in keeping your telescope aligned. They can save you a lot of time and frustration.
WHAT HAPPENS IF MY TELESCOPE IS NOT COLLIMATED?
The mirrors will be misaligned if you move the telescope or the temperature changes. When this happens, the images you see will be blurry. You may also see double images. To fix this, you need to collimate your telescope. If your telescope is out of collimation, you must correctly align the mirrors.