Telescope collimation is
the process of aligning a telescope's mirrors or lenses to ensure the light converges correctly at the focal point. Proper alignment is necessary for achieving sharp, clear images, and it is most commonly required for reflector telescopes.
When to collimate a telescope
- Blurry or distorted images: If your images look blurry or misshapen even when focused, your optics may be out of alignment.
- Star test failure: Point your telescope at a bright star and slightly defocus it. If the star's diffraction rings appear uneven, or if the dark shadow in the middle is off-center, your telescope needs collimation.
- Frequent movement: Collimation may be needed more often if you move your telescope frequently.
Collimation tools
- Collimation cap: This is a basic cap with a small peephole that fits into your focuser.
- Cheshire eyepiece: A Cheshire is a collimation tool with crosshairs for more accurate alignment.
- Laser collimator: A laser collimator provides the most precise and user-friendly method for collimation. It is highly recommended for beginners.
How to collimate a Newtonian reflector telescope
This process involves aligning the secondary mirror first, followed by the primary mirror. You may want to perform this procedure in the daytime initially to familiarize yourself with the process.
1. Align the secondary mirror
- Insert your collimation tool (cap, Cheshire, or laser) into the focuser.
- Look into the focuser. You will see the reflection of the primary mirror in the secondary mirror.
- Adjust the screws on the secondary mirror holder until the reflection of the primary mirror is centered.
- If you are using a laser, adjust the secondary mirror screws until the laser dot hits the center mark on the primary mirror.
2. Align the primary mirror
- Loosen the primary mirror's locking screws at the back of the telescope.
- Adjust the primary mirror's collimation screws until the reflection of the collimation tool (or the laser dot) is centered in the primary mirror's center ring.
- Once centered, gently tighten the locking screws to secure the mirror's position.
3. Fine-tune with a star test
- At night, point your telescope at a bright star (like Polaris).
- Defocus the star slightly. If the diffraction rings are not perfectly concentric, make small adjustments to the primary mirror's screws until they are centered.
I can also help you find a new collimation tool if you don't already have one, or provide a step-by-step guide for a specific type of telescope, such as a Schmidt-Cassegrain. Would you like me to find some options for you?