Beginners Telescope

Beginner's Telescope Collimation Guide

Collimation is the name given to aligning the mirrors or lenses in a telescope so that they reflect/refract the light into the eyepiece at the correct angle. Of all the beginner's telescopes we recommend, the only ones that will really need collimating are the newtonian reflectors. Our guide shows you how to collimate your telescope quickly and easily.

Collimation is something that will need doing at some point, so you may as well learn. Without it objects will start to appear blurred and you will lose detail. Depending on your telescope it may need doing every time you use it or only every now and then if your telescope gets knocked. Telescopes with larger apertures and shorter focal ratios (at this stage think of these as telescopes with shorter tubes) will need collimating more often and more accurately. However, don't worry if you can't get it perfect every time as most telescopes have a little bit of flexibility before it seriously affects your view.

If this all sounds very complicated, don't worry. It's one of the most technical things you'll have to learn with a new telescope but it really isn't as hard as it looks and once you get the hang of it won't take long at all.


Beginners Telescope Collimation Guide


What do I need?

There are three main types of tool sold to collimate a newtonian telescope. In many cases you can make do with the cheapest and simplest - a collimating cap. Later on you may want to use a cheshire collimator to improve your accuracy. Laser collimators are expensive and can need collimating themselves, so as a beginner you should probably give them a miss.

In addition you'll need whichever type of tool is needed to adjust the collimation screws on your telescope. Normally this will be an allen (hex) key or a small philips head screwdriver. Some telescopes will have thumbscrews which won't require tools.

Collimation Cap

This is a small plastic cap with a hole in the middle that fits into the focuser of your telescope. It often looks like a dust cap, but with a hole, and you may have got one with your scope. If not you can buy them for less than the price of a sandwich. If you really want to save money then you can make one yourself by finding a 35mm film canister and drilling a small hole in the centre of the base. These look far less technical than the other options but will do a perfectly good job on most telescopes.
US Supplier here
UK Supplier here
Telescope Collimation Cap

Cheshire Collimator

This works on the same principle as a collimating cap, but has an angled surface to reflect light into the telescope so you can see more easily. Some models also have a cross hair to make alignment of the primary mirror more accurate. For most of our starter telescopes the extra accuracy isn't required but may make it easier if you find collimation with a cap difficult.
Buy from Amazon US here
Buy from Amazon UK here

Laser Collimator

These fit into the focuser of your telescope and fire a laser into the secondary mirror that is reflected down to the primary. You can see if the laser is in the centre of each mirror quickly, so when they work they are very easy to use. However they cost much more than the alternatives and aren't required for the scopes we recommend. They can also need collimating themselves to ensure their accuracy. Unless you really want one for the shinyness you'd be better off with one of the other options. We won't cover these in detail, but basically you adjust each mirror so the laser hits the middle and bounces straight back into the laser emitter.
Buy from Amazon US here
Buy from Amazon UK here

How to Collimate a Newtonian Telescope

General Advice

  • Keep the tube of your telescope horizontal so nothing can fall down and hit the mirrors.

  • Aim your telescope at a well lit plain wall so you can see clearly when you look at the mirrors.

  • Check before you adjust - Your telescope might be fine and you don't want to make it worse! Most of the time a qucik check will be all you need at the start of your observing session.

  • Take your time - This can take a while to get right, especially at first. Don't rush. It's best not to try collimating for the first time when you are outside in the dark and wanting to get on with observing. Have a go during the day so you know what to do.

  • Make sure your primary mirror is marked in the centre with a small dot or ring. Most good telescope mirrors will be, but if not there are instructions on how to do it here.

  • Don't touch the surfaces of the mirrors.

Aligning the Primary Mirror

This is the most important step and probably the one that will need doing most often. It's also one of the easiest steps.

Locate the adjustment screws for the primary mirror. There should be three pairs. Usually the smaller screw is a lock screw and the larger screw is for the adjustment. You may need to remove a metal plate to access the screws - check your telescope manual.

Newtonian Telescope Primary Mirror Adjustment

Fit your collimating cap or cheshire collimator into the focuser of your telescope and look through it. Hopefully you will see something like the picture below.

Properly Collimated Newtonian Telescope

If the small black dot you can see in the reflection of the collimating cap is in the middle of the primary mirror like in the previous picture, then congratulations, your primary mirror is aligned. If it's off to one side, like in the next picture, then you need to carry on.

Uncollimated Newtonian Telescope

Pick an adjustment screw to turn. With practice you'll have a good idea which one to pick, but if not just choose at random. Loosen the locking screw and then make a small turn on the adjustment screw. Start with very small turns of 1/4 to 1/2 turn and then look through the focuser again. If you've moved the dot closer to the centre of your mirror well done, if not just turn the adjustment screw back. Then move onto another adjustment screw - you should be able to get the mirror aligned by adjusting two of the three screws. Use trial and error at first and then later you'll learn which adjustments do what.

Be careful not to either overtighten the screws or to loosen them so far they fall out.

Once the mirror is aligned gently tighten the locking screws for both of the adjustment screws you used. Check the mirror again to make sure tightening these didn't move the alignment.

That's the primary mirror aligned. With practice this won't take long at all, and you should be able to do it quickly before an observing session.

Aligning the Secondary Mirror

The secondary mirror is correctly adjusted if it appears as a circle when viewed through your collimator, with the clips holding the primary mirror all visible. The reflection of the primary mirror should appear to just fit on the secondary mirror.

There are two parts to aligning the secondary mirror. The first is making sure it is in the correct position and the second is adjusting the angle of the mirror. The secondary mirror is a flat mirror, so the most important thing is that it reflects the light from the primary mirror straight into the eyepiece. If the alignment is off you will lose the quality and brightness of the image, but it matters a lot less than the primary mirror and shouldn't need attention very often.

To adjust the position of the secondary mirror you need to turn the screws or knobs that are attached to the 'vanes' that hold the mirror in the middle of your telescope tube. Start by looking down from the top of your telescope check that the centre of the vanes is in the middle of the tube. You can check this with a ruler (measure that the distance down each vane from the edge of the tube to the centre is the same) or by cutting out a circle of card the same diameter of your tube and checking the centre lines up with the centre of the vanes. If it needs adjusting use the same techniques as we used with the primary mirror and make small adjustments to one vane in turn until the mirror is in the centre of the tube.

Newtonian Telescope Secondary Mirror Adjustment

On some telescopes the secondary mirror may be meant to be slightly off centre. Check your telescope manual and if it is follow the dimensions there to make the correct vane(s) slightly longer or shorter as required. If the manual doesn't mention it then the mirror should be in the centre of the tube.

Once the mirror is in position horizontally you need to check if it is aligned with the focuser. Again, fit your collimator into the eyepiece and look through it. You then need to see if the secondary mirror appears as a circle in the middle of the view - if you find this hard with all the reflections try putting a soft cloth or piece of paper down your telescope tube, between the two mirrors. This makes the secondary mirror easier to see. If you can't see the whole mirror then move your focuser out as far as possible to get a better view.

To adjust the secondary mirror there will be a central screw on the mounting that will move the mirror up and down in the tube. This may also allow the mirror to rotate slightly if required. Round this will be a number of smaller screws that adjust the tilt of the mirror, like the on primary.

Once you have the mirror in the centre of the focus tube and positioned so it looks like a circle in the view through the focuser you can move on to aligning it with the primary mirror. This requires adjusting the three small screws on the mirror mount.

The aim of this is so that the light reflected from the primary mirror all hits the secondary mirror - if it's off then you will be wasting some of the light that is collected. To see when this is happening, fit your collimator to the focuser, move the focuser in as far as you can, and then look through it (remove the card or cloth in the tube if you put it there earlier). Move the focuser out until you can just see the edge of the mirror. Adjust the secondary mirror's tilt until you can just see the clips holding the primary mirror in place reflected near the edge of the secondary mirror. Then make sure the edge of the secondary mirror follows the edge of the primary mirror.


Once you have done this you may need to readjust the position of the secondary mirror again in case it has shifted while you were adjusting the tilt. You may also need to readjust the primary mirror. Work through these steps repeatedly until everything is in place. Hoepfully in future you'll only need to do some minor tweaks to keep everything in place.


If you can't get the hang of it with our guide then why not try these alternatives.

AstroBaby's Guide to Collimation
Gary Seronik's Guide to Collimation