You will need to collimate all telescopes from time to time, but Newtonian telescopes are especially prone to collimation issues so we might need to collimate them more frequently.
In collimating Newtonian telescopes, you might wonder whether you’ll need a Cheshire collimator or a laser collimator to help do the job. The truth is, you can use both, but there are also some key differences between the two both in functionalities and benefits.
In this guide, we will discuss the main differences between a Cheshire vs Laser collimator, how to use them, and our product recommendations for both.
What is Telescope Collimating
Collimation is a process of aligning all components inside a telescope to ensure we get the most optimal focus from the telescope. All telescopes need to be collimated at some point, but the issue of misalignment is more prone in Newtonian (reflective) telescopes.
Schmidt-Cassegrain telescopes and their variants will also require collimation every time you set up these telescopes.
Collimating a reflector or Schmidt-Cassegrain telescope is relatively easy to do, and should only take a few minutes once you’re familiar with the process.
However, there are Schmidt-Cassegrain telescope variants like this Maksutov-Cassegrain that are relatively difficult to collimate (although they tend to hold collimation well).
For more information on different telescope types, be sure to check out our article here.
There are two different types of collimation, mechanical and optical:
- Mechanical collimation is performed when physical components inside the telescope are misaligned, for example when a secondary mirror is misaligned or when a focuser isn’t positioned dead-center.
- Optical collimation is performed to bring the image produced by the telescope to the correct focus/orientation
How Do You Collimate a Telescope
Here, we will mainly discuss how to collimate reflector and Schmidt-Cassegrain telescopes, respectively:
Collimating a reflector telescope
To collimate a reflector telescope, we recommend using a laser collimator, although you can also get a Cheshire collimator to collimate the secondary mirror.
It’s important to get the right size of a laser collimator depending on the size of your focuser.
For example, if your focuser is 1 1/4” in size, your laser collimator should also be 1 1/4”. Anything less in size can misalign the laser.
First, you should mark the center of your primary mirror. If you are using a laser collimator, then you will need a hole in the middle of this marker, and this is why using a white adhesive reinforcement ring is recommended.
There are also laser collimators that offer their own target labels so they will perfectly fit the collimator.
It’s very important to correctly place the marker dead-center on the primary mirror, or else the collimation process will go to waste.
In a reflector telescope, there are three objects that might need collimation: the focuser (including the eyepiece), primary mirror, and secondary mirror.
- First, ensure the secondary mirror is centered under the focuser. You can use a Cheshire collimator to check the position of the secondary mirror. Move the secondary mirror accordingly. The secondary should appear circular and center.
- Insert the laser collimator into the focuser (note: you can use Cheshire here, but using a laser collimator is much simpler). Adjust the secondary mirror with its adjustment screws until the laser falls on the marker you’ve previously marked on the primary mirror.
- Adjust the primary mirror to ensure the reflection is headed right into the very center of the focuser. Use the adjustment screws with the laser on to adjust the position of the primary until the laser beam returns to the laser collimator.
- In cases where the telescope is way out of alignment, you can point the telescope to any non-reflective surface (i.e. a wall), then change the mirror’s tilt by moving only two of the adjustment screws modestly.
Collimating a Schmidt-Cassegrain telescope
Collimating a Schmidt-Cassegrain telescope (SCT) will require an Allen wrench or Phillips screwdriver, depending on the model of your SCT. Typically you can find a plastic circle on the back of the secondary mirror’s mount with three adjustment screws.
You don’t need to use a Cheshire collimator or laser collimator when collimating an SCT, although they can help. Instead, you will need to do a star test and center the SCT on a relatively bright star:
- First, let the telescope thermally stabilize before the collimation process.
- Use a moderate to a high-magnification eyepiece (i.e. 10mm to 12 mm) and center on a relatively bright star (1st magnitude is preferred). If you are located in the Northern hemisphere, you can center on Polaris.
- Defocus this star to produce a donut shape, the ‘hole’ of this donut is actually the shadow of the secondary mirror. If it’s not dead-center, then we must collimate the SCT.
- Try tightening and loosening the three screws and check the position of the ‘hole’. If, for example, you are tightening a screw but the hole is moving further from the center, return the screw to its starting position and try tightening the other two.
- After adjusting the screws, return the star to the center by adjusting the telescope’s position. Now the image of the defocused star should produce a donut with a hole perfectly positioned in the middle.
What is a Cheshire Collimator?
A Cheshire Collimator is a rather simple hardware/device that looks just like your telescope’s eyepiece. The Cheshire collimator can come in many different lengths, and typically the size/length won’t matter much to its functionality. So, you can choose the size according to your preference.
While the design might vary between different Cheshire collimator products, typically they have a rubber cap with a small hole in the middle. This hole is where you are looking through during a collimation process.
Inside this rubber cap is a tilted mirror or reflective material with an aiming crosshair at the bottom. Since this reflective material inside the tube needs light to be visible, you can only use the Cheshire collimator during the day.
The Cheshire collimator is typically used for collimating a Newtonian telescope’s secondary mirror: simply align the secondary mirror under the Cheshire collimator’s focuser so that it must be dead-center as you are looking through the focuser while also reflecting the primary mirror in the center.
What is a Laser Collimator?
A Laser Collimator, as the name suggests, utilizes a laser beam to collimate the primary and secondary mirrors in a reflective telescope.
Unlike the Cheshire collimator that is typically used for collimating the secondary mirror, we can use the laser collimator for collimating both the primary mirror and the secondary mirror’s tilt.
However, it won’t help you in collimating the secondary mirror so that it’s properly centered in the focuser (as discussed, you’ll need a Cheshire collimator for this).
Typically you don’t need to collimate your secondary mirror too often unless the telescope is impacted by a hard object or you drop the telescope.
We will, however, need to collimate the primary mirror from time to time.
So, a laser collimator is typically a better investment, and it is also much easier and precise to use.
Cheshire Collimator Recommendation
While there are plenty of Cheshire collimator products available in the market, we’ve narrowed them down to one that checks all the boxes in terms of quality, usability, and cost. Our recommendation here goes to:
The brand Celestron obviously needs no introduction in the world of telescopes. Celestron manufactured really great telescopes, and they are also known for manufacturing some of the best collimation tools today.
As the name suggests, the Celestron Collimation Eyepiece 1.25” is a Cheshire collimator designed for reflector telescopes with 1.25” eyepieces, which are pretty common. It is very easy to use, and won’t take too much time to set up whenever you need to collimate your telescope’s secondary mirror.
- Ideal for precise collimation of Newtonian reflector telescopes, can also help in aligning Schmidt-Cassegrain telescopes
- Fits into 1.25” focusers or diagonals
- Easy alignment with a small pinhole on one end and thin crosshairs at the other end
- Accurate and easy to use
Pros and Cons
- Lightweight and compact (2x2x2 inches)
- Accurate collimation and easy to use
- Works with most Newtonian telescopes with 1.25” eyepiece
- Affordable and reliable
- Don’t use a laser beam, great for beginners
- No batteries required
- As a Cheshire collimator, hard to use at night (need daylight)
- Assembly might be difficult at first although there’s an included manual that will help a lot
Laser Collimator Recommendation
Similarly, there are plenty of Laser collimator products available in the market, again we’ve narrowed them down to one that checks all the boxes in terms of quality, usability, and cost. Our recommendation here goes to:
SVBONY, just like Celestron, is also a big name in the world of telescopes and astronomy. This Laser Collimator is a great product that can effectively help align both the primary and secondary mirror of your telescope:
- Lightweight at only 0.56 pounds
- 2.2 inches by 2.7 inches by 5.7 inches, compact in size
- CR2032 battery included
- Convenient rear-view port, allowing us to easily collimate optics from the rear of the telescope
- Aluminum housing with a wide 3mm barrel flange to ensure proper seating
- Fits any 1.25” telescope eyepiece holder
- Includes extra center mark collimation target labels for primary mirrors
- Comes with a 2 inch adapter for 2 inch focusers.
Pros and Cons
- Fits tightly into the eyepiece holder, not easily come loose
- The rear-view feature is very useful especially if you don’t have a friend to help with the collimation
- Extra marker included, which will perfectly fit the LaserMate
- Easy to set up and easy to use
- Battery included
- Works with any telescope with a 1.25” eyepiece holder
- Laser beam not pre-collimated
- Not the most affordable option