Telescope Collimation Tools: Cheshire, Lasers & More

What does collimation mean?

Collimation aligns optical components so that light travels correctly through the telescope and forms the sharpest possible image at focus. It is especially important in Newtonian telescopes, where the secondary and primary mirrors must be positioned relative to the focuser and optical axis. Misalignment can show up as soft stars, asymmetric diffraction patterns or reduced sharpness at higher magnifications. Seeing, telescope cooling and focus also affect the view, so not every soft image indicates a collimation problem.

Which collimation tool should you choose?

Cheshire eyepieces and collimation caps make the geometry inside a Newtonian visible. A Cheshire uses reflections and, where present, the primary mirror centre mark to assess alignment. Models with a crosshair also help check the position of the secondary beneath the focuser. Check the product details: not every Cheshire tool covers every adjustment step. Some models are also specified for particular refractors or Schmidt-Cassegrain telescopes.

Concenter eyepieces show concentric rings that help assess the secondary mirror position and the view of the primary in a Newtonian. Models are available for 1.25-inch and 2-inch focusers; some versions offer illuminated circles or features for eyeglass wearers. Follow the instructions for interpreting the rings and any secondary offset for the specific model.

Laser collimators project a beam along the focuser axis and can simplify Newtonian alignment, especially when working alone. Check the barrel size, secure fit and reliable centring. The laser itself must be collimated: an incorrectly aligned laser can give a false impression of telescope alignment. Insert it consistently without tilt and use the manufacturer’s method for the secondary and primary mirrors. The correct return-beam procedure depends on the tool. Never point a laser at eyes or other people.

Artificial stars provide a defined test target when no suitable star is available. Depending on telescope design, aperture and test distance, they can be used for alignment or optical testing of compatible instruments. The artificial star must be placed far enough away; the required distance depends on the instrument and test. Follow the manufacturer’s guidance, as a target that is too close may not produce a result directly comparable to a star in the sky.

Consider the telescope design

• Newtonian telescopes: Cheshire, Concenter and suitable laser tools are commonly used to check the secondary and primary mirrors. A centre mark on the primary helps with many methods. Work step by step and turn only the adjustment screws described in the manual.
• Refractors: many refractors are aligned at the factory and do not need regular user adjustment. Use a tool or test method only if the model is designed for it.
• Schmidt-Cassegrain and other catadioptric telescopes: their alignment procedure differs from a Newtonian’s. Do not apply Newtonian instructions universally; follow the guide for the specific telescope.

Fitting and careful use

Check whether the tool fits a 1.25-inch or 2-inch focuser and whether an adapter is required. For repeatable results, it needs to sit straight without tilt. Clamping screws, compression rings and adapters can affect its position, so insert the tool as you would an eyepiece. Collimate with the telescope securely supported, then check the result on a star or with the method recommended by the manufacturer.

What to check before ordering

• Which telescope design are you aligning or testing?
• Which components are adjustable, and what steps does the telescope manual describe?
• Does the 1.25-inch or 2-inch fitting match, and is the laser itself aligned?
• Can you place an artificial star at a suitable distance?
• Does the tool include the reticle, crosshair, rings or adapters needed for your intended use?

Browse more telescope accessories in the parent category.