All astronomers — beginners and experienced — must learn to collimate a telescope. Telescope collimation is necessary every so often to ensure bright, sharp, undistorted images when you observe the night sky. Conversely, a poorly collimated telescope will show blurry images lacking detail. So, to get things back into focus and make stargazing enjoyable, collimating a telescope is necessary from time to time.
This article is a complete guide to collimating your telescope. In addition, you will find answers to common questions about telescope collimation and how to adjust the lenses and mirrors of various types of telescopes.
What Is Telescope Collimation?
Collimation is an adjustment to the telescope’s mirrors and lenses, allowing for the best possible imaging. Collimating a telescope involves pointing the primary mirror at its optimal focal point. This reflects light at the correct angle on the secondary mirror. Additionally, it’s necessary to align the eyepiece and secondary mirror.
There are two types of collimation — mechanical and optical. Mechanical collimation requires you to line up the physical components of the telescope so that light is reflected at the proper angles. Optical collimation aligns the scope’s optical surfaces so that the image is in the correct orientation.
Collimation is just another word for alignment. It is an easy process and can significantly enhance your experience when observing the planets in the solar system, stars, and moon.
How To You Know If A Telescope Needs Collimation?
Blurry images are the most common reason to align or collimate a telescope. For example, lunar craters may appear blurred out. Or you might not get a crisp image of Jupiter’s belts. And the rings around Saturn could make the planet look like a teacup with two handles.
However, how can you tell if the blurry images are because of a misalignment with telescope mirror and lenses or if it’s because of other issues?
Here’s the “star test” to know if you need to collimate your telescope:
- On a clear night, focus on the brightest star, for example, Sirius.
- Center the star in your field of view.
- Zoom in as much as you can, keeping the star in focus.
- Next, slowly defocus the star, and circles should appear around the object.
- Observe the shape of the rings — are they concentric or eccentric?
You know the telescope requires collimation if the circles are eccentric (i.e., not having a common center or appearing wiggly).
How Often Should You Collimate A Telescope?
The frequency you collimate a telescope depends on the type of telescope and how often you move it. Some telescopes only require collimation when first set up or after being moved. Others need to be collimated each time they are used. However, some stargazing enthusiasts spend hours tweaking the scope’s optics to get perfect images.
Different types of telescopes require collimation at different times. Here is a list of when to collimate the most popular scope types:
- Schmidt-Cassegrain telescope—Requires collimation once or twice a year. However, you will need to realign the refractors if you drop it or bump it.
- Newtonian telescope—It’s typically necessary to collimate a Newtonian or reflector telescope before most observing sessions. The mirrors in Newtonian scopes easily become misaligned.
- Dobsonian telescope—Depending on the scope’s design and build, a Dobsonian telescope may need slight collimation between each session.
For most astronomer enthusiasts, collimating your telescope is a necessary task to do from time to time. Typically, the larger the telescope, the more often you’ll have to do it. If your telescope is not collimated, you will not see the best image that it can give you.
What Happens If You Don’t Collimate Your Telescope?
Without proper collimation, your telescope cannot provide sharp images of stars and planets. The images the telescope shows will be without sharpness and be fuzzy or blurry. However, some beginners don’t notice anything different in the views through the eyepiece — especially if it’s their first time using a telescope.
Over time, and with repeated use, telescopes that haven’t been collimated become less precise. As a result, the images in the eyepiece appear off-centered and of poor quality. Aligning the primary mirror with the secondary and then adjusting the eyepiece brings the image back into focus.
The good news is that it only takes a few minutes to align your scope’s optics properly, and it’s easy to do.
Which Telescope Does Not Need Collimation?
Most refractor telescopes are permanently collimated and generally don’t need frequent realignment. These scopes include designs such as a Schmidt-Cassegrain telescope and a Maksutov telescope designed with built-in corrector plates. However, you may still need to collimate these occasionally, depending on how you use them.
In essence, all telescopes require some form of collimation from time to time.
How Hard Is It To Collimate A Telescope?
Collimating a scope is not tricky. However, this is a precision task you should tackle carefully and accurately. Of course, the first time you collimate your telescope may be a bit intimidating. Collimating a scope requires adjusting the collimation screws and aligning the mirrors and lenses to get a sharp picture of objects in the night sky.
How Do I Collimate My Telescope?
Collimating a telescope requires minuscule corrections, turning one screw at a time to align the mirrors and lenses. You will need an appropriate screwdriver and some patience to collimate the scope. Before collimation, it’s vital to let the telescope thermally stabilize to the ambient temperature.
The fastest way to align a telescope is to use a laser collimator. This device lights up inside your scope with a laser pointer, which you can then align with the other mirrors. This way, you can ensure that everything is lined up perfectly without resorting to the star test.
Here is how to collimate a telescope with a laser device:
- Remove the eyepiece from your telescope and attach the laser device.
- Turn on the laser collimator and look through the focuser of your scope.
- Next, look for the spot or dot of light on one of the mirrors.
- The dot should be dead center.
- If not, loosen the three tiny screws and adjust the mirror until the dot is centered.
- Then tighten the screws to collimate the telescope.
- The next step is to adjust the rear (primary) mirror so that the laser dot shows up in the center of the bullseye.
How Do You Collimate A Refracting Telescope?
Collimating a refracting telescope involves adjusting the mirrors so that light rays converge at a single point. An accurately aligned scope will result in better resolution and crystal-clear images. How can you collimate a refracting telescope? Here is a short guide:
- Point the telescope at a moderately bright start like Polaris or Sirius.
- Defocus the image so that you see a ring or doughnut of light.
- There are three adjustment screws on the back of the secondary mirror’s mount.
- Make minor corrections, adjusting one screw at a time to align the hole so that it’s centered in the doughnut.
- Then adjust the focus until you see the diffraction rings and use them as a guide to fine-tune the collimation.
How Do You Collimate A Reflector Telescope?
Collimating a reflector telescope is more challenging because it requires aligning three things — the eyepiece, primary mirror, and secondary mirror. So, during the daytime, identify these parts to know what they look like in the scope. But, how can you collimate a reflector telescope? Here is a short guide:
- Slide a sight tube (Cheshire) into the focuser, like you would an eyepiece.
- Look through the hole and tilt or rotate the secondary mirror to center the spot’s reflection under the crosswires.
- Next, align the primary mirror using the adjustment screws.
- Collimation is complete when the peephole spot is centered on the primary mirror.
Conclusion
The best results from stargazing are when you have a properly collimated telescope. Collimation is a simple process that takes five to ten minutes, and it’s well worth taking time to do this. For most amateur astronomers, periodic maintenance and collimation are an essential part of the hobby. With practice, you can become consistently accurate and take pleasure in observing the night’s sky.
