Telescopes are precious pieces of hardware. The delicate nature of the lenses means that a telescope cannot perform optimally if its lenses are not in proper working condition. That’s why whether you are an amateur or professional, you need to know whether your telescope needs collimation or not.

If you are having trouble focusing on deep sky objects, then the chances are high that your telescope needs collimation. Lenses that are scratched up can also make it hard for you to focus on the objects with your telescope.

This article will talk about how you can identify if your telescope needs collimation. It will also be a guide to properly collimate your telescopes, so read below to get a beginner’s guide on this topic.

What Does Collimation Mean?

The physical alignment of your telescope’s lenses is known as collimation. Even in perfect night sky conditions, you will find it impossible to get the focus of deep-sky objects with your telescope if it is not properly collimated. Refractor telescopes cannot be collimated due to their optics. On the other hand, if you have a reflector telescope or a Newtonian telescope, then you can collimate your telescope.

How Can I Identify If My Telescope Needs Collimation?

Telescopes that are not collimated will perform poorly. That is why it is very important to check for collimation before you head out on your next stargazing trip. To properly collimate your scopes, you would need to point your telescope to a star. The star can be artificial or real.

You can also take the help of lasers or Cheshire eyepieces to collimate, but it is very hard to collimate accurately with lasers. So the ideal way to do it is with a star.

Artificial stars are easier to collimate with as they don’t suffer from environmental conditions. With that being said, it is not ideal to use artificial stars when you are in an open field. That’s when you need to use a real star to collimate your scope.

At first, you need to pick one of the brightest stars in the night sky. Sirius is a popular choice because it is very bright and even visible during gloomy atmospheric conditions.

Then you need to point your telescope to the star. Bring this star into the central point of view of your scope, and utilize your lenses to zoom into the star. Max out your zoom and see if the star is in focus or if it appears to be hazy in the display.

After you do this, you need to slowly defocus this star by zooming out of focus. You will notice a set of concentric circles when you zoom out of the star. The diffraction does not have to nicely centric, the pattern only needs to be circular in appearance.

Once you complete this procedure, you have to analyze the patterns of diffraction. There will be a dark center with concentric circles around it. A collimated telescope will be able to display perfectly centric patterns, while a telescope that needs collimation will show misaligned optics.

What's in the Night Sky?

How To Collimate Your Telescope Optics?

Now that you know why you can’t focus properly on the Moon, it is time to fix the problem. There is a quick fix that you can employ to collimate your scope, and that is to adjust the secondary mirror of your telescope. If the problem is small, this quick fix can collimate your scopes adequately. Please note that this is not the only way to collimate as it can vary wildly depending on the type of scopes that you are using.

How To Collimate By Adjusting The Secondary Mirror

Reflector telescopes such as the Newtonian use optically mirrored scopes. These types of telescopes have a secondary mirror that is usually mounted on the front. This mirror is helped onto position by a glass pane or spider. You can spot some adjustment screws near this mount, which are evenly spaced.

Do not, under any circumstance, touch the secondary mirror with your hands or any other objects. You should always practice extreme caution while adjusting the secondary mirror, and touching the glass panel may cause damage to your scope.

Adjusting The Screws Of The Secondary Mirror

There are three screws near the mirror, and adjusting them will cause a push or a pull effect on the mirror. This will, in turn, result in the light being properly aimed at the mirror, enabling it to reflect accurately on to the lenses. If you tighten or loosen the screws, you will be able to move the secondary mirror. This will result in moving the circles inside the diffraction patterns to pull or push closer from that particular direction.

Once you have a clear idea of the diffraction patterns, you can start this process. You can connect the camera viewfinder to a computer so that it constantly displays the concentric circles. Then you need to pick one of the three screws and adjust it slowly. Tighten or loosen the screws ever so slightly, and see the results on the display. Take a mental note of which particular screw you adjusted and which side you turned it to.

If the diffraction patterns get worse, you need to move back the adjustments you made on the screws. If the diffraction patterns get better, to form perfect concentric circles, then you need to keep turning the screw more until the patterns become perfect.

Every time you make a slight adjustment by loosening or tightening the screws, you will witness that the diffraction patterns move in a particular direction. The more you keep doing these adjustments, the better you will get the hang of it. Remember that these screws operate via a pull/push effect on the mirror.

If you are not finding the desired results by moving one screw, then move to a different screw and take note of how its adjustment affects the diffraction patterns. The first time you will be performing this, you might feel like it is difficult to collimate. But the more you attempt this procedure, the more sense it will make and the quicker you can complete this fix.

Repeat this procedure until you can move the patterns of diffraction more predictably. Once you can get the circles to be as concentric as possible, you will know that your scopes are properly collimated. Please note that you need to have even gaps that are inside these perfectly circular circles.

Another thing that you can do is that if you feel like one of the adjustment screws are tighter than it should be, you can loosen another screw which is on the opposite side of the mirror.

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Equipment you need to collimate your telescope

There are several methods for collimating your telescope, so let’s look at some of the more common ones.

Collimation cap method

A sight tube, also known as a collimation cap, is essentially a plug that you insert into the focuser of your reflector telescope. It can be used to ensure that your telescope’s secondary mirror is properly aligned with your focuser, as well as that both mirrors are aligned with each other.

To use a collimation cap to collimate your telescope, first put it in the focuser and look at the primary and secondary mirrors. 

Everything will be perfectly aligned if the telescope is collimated. If they appear to be out of sync, you’ll need to take the next steps to correct the collimation problem.

  • If you peek into the cap, you’ll find that the underside is reflected in the primary mirror of the telescope. You’ll also notice a reflection of the hole in the cap through which you’re gazing – it appears as a black dot on the mirror’s surface, right?
  • Your primary mirror needs to be adjusted. You’ll do this by turning the collimation knobs (found on the scope’s back end) until the dot appears in the middle of the mirror. 
  • It’s not difficult, so take your time. Continue moving knobs until you notice the dot centering a little more. Stop and adjust the knob in the opposite direction or try a different knob if it causes it to become more out of sync.
  • After that, you must orient the secondary mirror to ensure that it will effectively bring all of the primary mirror’s light to the telescope’s eyepiece. Examine the primary mirror’s outside circumference and the secondary mirror’s outer edge in the collimation cap. The secondary mirror often has a number of adjustment screws, which might be frustrating, but you don’t have to move them very often.
  • The distance between the top of the tube and the focuser’s center should be measured with a tape measure. The distance from the top of the tube to the middle of the secondary mirror should be the same (via Gary Seronik). If the measures are out of whack, unscrew the large nut or screw and adjust the screws back and forth.
  • Adjust the tilt so the primary mirror’s outer edge and the secondary mirror’s outer edge are concentric. This may necessitate the use of a hex wrench or screwdriver.
  • You should use the focuser with the rack all the way in. You know you’ve struck gold when the primary mirror’s outer edge is practically touching the secondary mirror’s outer edge.

Can you make your own collimation cap?

Absolutely! Here’s how to do it.

You’ll need the following items:

  • An eyepiece cap or a film canister – simply cut off the canister’s end
  • Drill bit for small holes
  • Paper/Pencil


  • Drill a hole in the cap of your eyepiece or the film canister. This hold must be drilled in the exact center of the item.
  • Take a piece of paper and trace the eyepiece cap or canister on it to guarantee that the hole will be exactly in the middle before drilling it. Remove it. The paper should be folded into four symmetrical squares and then unfolded. The midpoint is the point where the lines intersect.
  • Then, using tape, secure the paper to the cap (or canister cap).
  • After you’ve double-checked that everything is straight and level, drill a hole in the center.

Other tools you could use to collimate your telescope

Cheshire eyepiece

A Cheshire eyepiece is a collimating eyepiece for your telescope. It’s essentially a sight tube with a hole at the top (through which you gaze) and a 45-degree-tilted surface pointing at a hole in the telescope’s side.

Some Cheshire eyepieces contain cross-hairs at the bottom of the tube to aid in the alignment of a reflector telescope’s secondary mirror. It’s simple to use and precise.

Here’s how to put it to use:

  • Place the Cheshire in the focuser while looking in the primary mirror at the reflection of its face. 
  • Adjust the adjustment screws on the primary mirror so that the reflection can be shifted all the way to the center.
  • Three adjustment screws or pairs of pull-push settings are found on most mirrors. Only use two of them. Only use the third screw if the first two screws have failed to assist you to collimate the telescope. 
  • Because the secondary mirror is slightly out of sync, the Cheshire eyepiece will not always be properly centered in the shadow of the secondary mirror; nonetheless, this isn’t a problem (via Sky and Telescope).

Laser collimator

This method of telescope collimation is quite quick, but you will require a laser collimator. This is inserted into the focuser of the telescope, which produces a beam. If the beam fails to hit the secondary mirror, the telescope is out of sync and requires collimation. You’ll need to direct the beam to a wall in order to make modifications.

This is how you do it:

  • First and foremost, insert the laser collimator into the telescope’s eyepiece holder. Make sure it’s pointed in the direction of the telescope’s rear.
  • Turn on the laser collimator and aim it at a wall. A red dot on the wall should not be visible, as this indicates that the collimation is significantly off. If the laser does not leave a dot on the wall, you can safely gaze into the optical tube to collimate the telescope, therefore don’t skip this step! 
  • You may now adjust the secondary mirror of the telescope. For this, you’ll need an Allen wrench. When the laser is turned on, look into the optical tube to see where the laser impacts the mirror. There’s also a dot in the center that comes from the primary mirror. 
  • Loosen or tighten the tiny adjustment screws with care. When you loosen or tighten them, the secondary mirror of the telescope is pushed forward, causing the laser to bounce in a new direction. These screws must be adjusted such that the laser’s red dot is inside the little circle on the primary mirror. Don’t overtighten the screws since the secondary mirror holder may break
  • You’ll want to adjust the primary mirror on the back of the telescope after you’re pleased. 
  • Turn the three adjustment knobs by loosening the thin and long lock screws.
  • These functions are similar to the screws for the seconary mirror. Turn the knobs until you see the laser steadily approaching the middle of the target’s bullseye. One of the advantages of using a laser collimator is that you can change the screws and knobs while looking at the target image without having to run around to the other side of the telescope. 

Things You Need To Do To Properly Look After Your Telescope

You cannot touch any lenses or glass surfaces of the mirrors. If you do so, your lenses can get easily scratched up and this may affect your viewing experience. A scratched-up glass surface is very hard to fix, and you may need to buy new lenses altogether.

Practice great caution while using your telescope and do not drop any objects on the mirrors or the tubes of the telescope.

Collimation is a delicate thing, and you need to do it in a very steady way. The more you adjust the mirror, the more your star will move. If you move too much, you may need to re-center your scope. While performing collimation, you should keep your mount controls in your hand.

Some telescopes tend to throw off the collimation as soon as you point it towards the opposite part of the night sky. This can be a bit frustrating for people.

This guide does not talk about the full procedure to perform collimation. A telescope that needs collimation also needs adjusting of its primary mirror, which this article does not talk about. This procedure is more intricate and requires a lot more experience. This article only talks about a quick fix, and most telescopes that lose focus can be quickly collimated by performing this procedure.


Do you need to collimate refractor telescopes?

These telescopes are normally permanently collimated when they are manufactured, so you will almost certainly never have to do so. However, if you’ve dropped or bumped them hard, it’s worth double-checking.

How often should you collimate a reflector telescope?

It’s important to remember that some telescopes, such as reflectors, will require collimation every time you want to set them up, such as if you’ve relocated them from one stargazing spot to another. As a result, you’ll have to check them on a regular basis.

How often should you collimate a telescope?

In most cases, if you don’t transfer your telescope by automobile and don’t treat it badly during routine use, you won’t need to collimate it. Perhaps once every few months. Because I carry my Heritage 130p in a duffel bag, I do rapid collimation most of the time I set it up.

What is the best time to use a telescope?

The greatest periods to stargaze are in the autumn, winter, and spring, which many astronomers refer to as an ‘observing season.’ This is the time between when the clock falls back in October (nights get one hour shorter) (nights become 1-hour shorter).

Final Thoughts

Although the telescope can appear to be a very complex object, it only has three optical parts. Common reflector telescopes such as the Newtonian has a primary mirror, a secondary mirror placed in the front, and an eye scope with magnification capabilities. Out of these three components, only the eye scope and the primary mirror has active optical parts.

All you need to do to ensure your scopes are properly collimated is that the eye scope is aimed at the dead center of the primary mirror and vice versa. If both these pieces are properly aligned, then the objects you will be viewing from the scope are in focus.

That is all you need to do. At first, it may seem to be daunting, but once you get a hang of doing collimation, it will only take a minute or two to get this done. Every time you go stargazing, you just need to ensure that the optical elements of your telescope are working in good condition.

Most of the time, you don’t need to do anything. On the offhand that you find your telescope to be out of focus, simply adjusting the secondary mirror can do the trick!