How Do I Know If My Telescope Needs Collimation?

The lenses of a telescope are a delicate thing, and they need to be cared for if you want to view the stars properly.

That means that at some point the telescope will need collimation. Collimation is the process of realigning the optics. You will often know a telescope needs collimation because the image has become blurry.

Collimation does, initially, sound like an intimidating task. Caring for a telescope properly requires a huge amount of precision, and a particularly delicate touch.

However, collimation doesn’t need to be scary. Essentially, all collimation means is aligning your telescope. When everything is properly aligned, the telescope is able to collect the light it needs for a clear image.

Collimation simply takes things that are in the wrong place, and puts them back. When the telescope isn’t correctly aligned, it’s impossible to get it to focus. Images will remain blurry, no matter what adjustments you make.

If you’re curious about whether your telescope needs collimation, then it’s likely because you can’t get your images into focus. If the images remain clear and crisp, then your telescope doesn't need collimation.

When your images are looking blurred or hazy, it’s possible that your telescope needs collimation. However, there may be another factor causing the problem. To be sure that it’s an issue with alignment, there are a few tests you can do.

The easiest test is the “star test”. All you need is a dark sky, a single bright star, and your telescope.

  1. Wait for a clear night, with limited haze. Cover and blur can affect the accuracy of this test.
  2. Pick a bright star in the sky, such as Sirius. Bright stars are the easiest to focus on.
  3. Center the star in the field of view (or as close to center as possible). Focus, and zoom in as much as you can. Using an eyepiece helps to increase the zoom. Once your zoom is maxed out, the star will likely be hazy if the alignment is off.
  4. Now, you want to defocus the star. Slowly bring the star out of focus, keeping your eye on the image.
  5. As you lose focus, monitor the diffraction pattern. The diffraction pattern is a series of concentric circles that appear around the star.
  6. If the circles are wobbly, out of line, or not concentric, then your telescope needs collimation. To put it very simply, a donut shape should appear around the star. If the center of the donut is out of line, then collimation is required.

There are other ways to check for collimation using lasers and Cheshire eyepieces. However, these tend to be unnecessarily complicated. As the star test is accurate, it isn’t really worth trying another way. After all, it’s the stars that we want to be seeing.

The biggest issue for beginners using the star test is correctly identifying a misaligned circle. Take your time, and repeat the process as often as needed. Once you know what to look for, it’s a lot easier.

How often do you collimate a telescope?

With proper care and attention, a telescope should not need collimation very often. Collimation is required when the inner optics of the telescope are out of alignment.

When this occurs, the telescope won’t be able to focus properly. If a telescope needs collimation, it is possible to fix it at home. 

When you purchase a telescope, it should be adjusted to factory settings. That means that all the optics are perfectly in place, allowing you to enjoy the night sky in all its glory.

However, transporting the telescope can cause things to move about. Because the telescope is such a delicate instrument, even a minor misalignment can end up causing big problems.

You’ll likely notice that your telescope requires collimation because you’re unable to get it to focus properly.

The more the telescope is moved, the more likely it is that the optics will misalign. Carrying a telescope to and from a site, moving it around the home, and even changing temperatures can all affect the workings of a telescope. 

It’s practically inevitable that at some point your telescope will need collimation. The only way to avoid it is to never use your telescope, and that’s no fun at all. Even a telescope that sits in a room and is never disturbed can potentially fall out of alignment. 

However, with careful care, it’s likely that your telescope will only need collimation roughly once a year. To delay the need for collimation, move the telescope carefully, keep it in the case when you can, and store it in the right environment.

This can limit the potential harm, and keep all those optics in place. Otherwise, a telescope may need collimation as often as every two months.

The good news is that once you’ve had to collimate the first time, it no longer seems so intimidating. Collimation using the secondary mirror is a delicate procedure, but one that any steady hand can achieve. 

While the actual collimation shouldn’t need to happen very often, checking for collimation should be a regular occurrence. When you set up for a night of stargazing, do a quick “star test” to see how well the optics are doing.

Getting into the habit of doing this quick test ensures that you’re more likely to notice when problems do occur. It can be a habit to dismiss blurry images as bad conditions, when in reality the telescope is causing the distortion.

Knowing when to collimate also has the advantages of knowing when you don’t need to collimate. For example, when the telescope is adjusting to the temperature, when the night is hazy, and when the lens needs cleaning.

If you own a refractor telescope, you cannot collimate it. Which isn’t to say that it won’t necessarily need doing. A refractor telescope should come from the factory permanently collimated.

This means that none of the optics should ever misalign. However, it does happen on occasion. If you think your refractor telescope needs collimation, the best thing to do is contact the manufacturer. 

Gordon Watts
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