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What is Collimation in Telescopes?

Collimation is the process of aligning all components in a telescope to bring light to its best focus. Most manufacturers collimate telescopes before shipping, but they often require recollimation to achieve the best image. When a telescope is out of collimation, celestial objects may appear blurry. 

What Are the Types of Collimation in Telescopes?

There are two types of collimation: optical and mechanical. Optical collimation aligns a telescope’s eyepiece and mirrors to bring the image into focus. Mechanical collimation requires you to manually adjust the physical components in your telescope. This can be caused by misalignments in your tube, focuser or mirrors. 

Why is Collimation Important in Telescopes?

In order to bring light into its best focus, telescopes must be collimated. Most refractor telescopes don’t require frequent collimation, unless they are bumped or shaken out of collimation. On the other hand, reflector telescopes require collimation more often. Experts recommend checking reflector telescopes frequently in order to minimize the collimating process. Fortunately, it’s quite simple to check if your telescope is out of collimation.

How Do You Know When a Telescope Needs Collimation?

If stars appear blurry or distorted, you may need to collimate your telescope. However, these symptoms aren’t always caused by collimation. To ensure your telescope is out of collimation, you can follow these steps.

  1. Focus on a bright star in the center of your field of view
  2. Carefully defocus the star and analyze the diffraction pattern
  3. If circles around the star are not concentric, you will need to collimate your telescope 

What Tools are Used for Collimation in Telescopes?

There are a number of tools used to collimate your telescope. The most important tool, to adjust the lens screws, is a screwdriver. To provide a point of reference during collimation, there are a number of telescopic devices . 

  1. Cheshire collimator: A small, circular tool with a hole in the center and a reflective surface, used to view the reflection of a star in the telescope’s mirrors.
  2. Collimation cap: A small plastic cap that fits over the focuser and has a hole in the center, used to view the position of the primary mirror in the telescope.
  3. Laser collimator: A device that projects a laser beam through the center of the telescope’s optics, allowing you to see the position of the mirrors and make adjustments.

How to Collimate Telescopes with Collimation Caps or Cheshire Collimators?

Collimation caps typically come with most reflectors nowadays. However, you can easily make your own if necessary. To do this, you can get a film canister, cut the bottom off, and poke a small hole in the lid. If you can afford it, buying a Cheshire will simplify the process and provide more accurate collimation. Collimating your telescope with a Cheshire or collimation cap is simple. First, make sure the secondary mirror is aligned accurately. To do this, ensure you can see the entire primary mirror with an even ring of the tube walls around it.  Next, you must align the primary mirror. To align the primary, adjust the three collimation bolts until it is aligned with the secondary mirror.

How to Collimate Telescopes with Collimation Lasers?

Refractors, which use lenses to focus light, telescopes typically require more frequent collimation. The quickest way to collimate a refractor is by using a laser collimator. This will be placed into the draw tube, where the eyepiece usually sits. Then, you must lock the collimator into place, facing the back of the telescope. A laser dot will appear on the surface of the primary mirror. To collimate your telescope, you must center this dot in the mirror. This is done by adjusting any two of the three screws on the secondary mirror until the dot is centered. 

How to Keep your Telescope Collimated?

In order to reduce the frequency of collimation, it’s important to keep your telescope well maintained. By following the 6 tips below, you can protect your telescope from becoming out of collimation.

  1. Store your telescope in a dry and stable environment.
  2. Handle your telescope with care.
  3. Check your telescope’s collimation regularly.
  4. Use protective covers when transporting.
  5. Be careful with temperature changes.
  6. Use the right tools and processes to collimate.

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