Laser Collimator Guide: How to Collimate Your Reflector Telescope

Quick Answer: What Collimation Tool Should You Buy?

The Celestron Collimation Eyepiece (Cheshire-type) is the best first collimation tool for most reflector owners. It is simple, requires no batteries, and teaches you to understand the optical alignment visually. For faster collimation in the dark, a laser collimator is the upgrade choice — insert it into the focuser, turn it on, and adjust the mirrors until the laser beam returns to its source. Expect to spend $20–$40 for a basic Cheshire eyepiece and $40–$80 for a reliable laser collimator. Our step-by-step guide below works with both types.

What Is Collimation and Why It Matters

Collimation is the alignment of all optical elements in a telescope so that light travels along the correct path from the front of the tube to your eye. In a Newtonian reflector (the most common type that requires collimation), you need to align two mirrors: the large primary mirror at the bottom of the tube and the smaller secondary mirror near the top.

Why it matters more than many beginners realize: an out-of-collimation telescope cannot deliver sharp focus at high magnification. Stars appear comet-shaped or have a "seagull" flare on one side. Planetary detail blurs. The problem gets worse at higher magnification — exactly where you need sharpness most. A telescope that is perfectly collimated will outperform a larger telescope that is poorly aligned.

How often should you collimate? Transporting a telescope almost always knocks it slightly out of alignment. Even moving it from indoors to a observing spot in the yard can shift the mirrors. The rule: check collimation at the start of every observing session. It takes 5 minutes and guarantees you see the best your telescope can deliver. Tabletop Dobsonians with collapsible tubes (like the Heritage 130P) need checking more frequently because the collapsing mechanism introduces slight play.

For a Dobsonian-specific walkthrough with photos, see our dedicated Dobsonian collimation guide.

Types of Collimation Tools

There are three main types of collimation tools, each with different strengths. Choosing the right one depends on your budget and how comfortable you are learning the process.

Recommendation: Start with a Cheshire collimation eyepiece. It teaches you the visual cues that matter, requires no batteries, and is indestructible. Once you are comfortable, a laser collimator saves time in the dark. Some experienced users own both. Avoid ultra-cheap laser collimators under $30 — they are often poorly collimated themselves, meaning the laser beam is misaligned with the collimator body, introducing errors rather than fixing them.

Step-by-Step Collimation Workflow

This workflow works for both Cheshire eyepieces and laser collimators. Follow these steps in order.

Step 1: Prepare the Telescope

Point the telescope at a bright wall or daytime sky (never the Sun!). Remove the eyepiece and insert the collimation tool into the focuser. Tighten the focuser thumbscrew snugly. If using a laser, turn it on and check that the beam is centered in the drawtube.

Step 2: Align the Secondary Mirror

Look into the collimation tool. The secondary mirror should appear centered in the focuser drawtube — an evenly spaced ring around the secondary mirror holder. If it is off-center, adjust the center screw on the secondary mirror holder (the one that attaches it to the spider vane). Loosen it slightly, center the mirror, then tighten. Do not confuse this with the three smaller tilt adjustment screws.

Step 3: Tilt the Secondary Mirror

Now adjust the three small tilt screws on the secondary mirror holder so that the primary mirror reflection is centered in the secondary. With a Cheshire, you should see the primary mirror's center marker (if your telescope has one) centered in the crosshairs. With a laser, adjust the tilt screws until the laser beam hits the center of the primary mirror.

Step 4: Align the Primary Mirror

This is the final and most common adjustment. Using the three collimation knobs at the rear of the telescope tube (behind the primary mirror), tilt the primary mirror until the collimation tool shows everything centered. With a Cheshire, the three clips holding the primary mirror should be evenly visible around the edge. With a laser, adjust until the returning laser beam hits the center of the collimator's target.

Step 5: Verify with a Star Test

Point the telescope at a moderately bright star (magnitude 2–3) at medium-high magnification (100–150×). Defocus slightly: a properly collimated telescope shows concentric rings around the star. An out-of-collimation scope shows lopsided rings. If the star test shows uneven rings, make slight adjustments to the primary mirror collimation knobs while watching the star, then re-center.

Recommended Collimation Tools

Editor's Pick — Best First Collimation Tool

Celestron Collimation Eyepiece (Cheshire)

This is the standard recommendation for any reflector owner. It is a Cheshire-type eyepiece that slides into the focuser like a normal eyepiece. Look through it, and you see crosshairs and reflection rings that show you exactly how your mirrors are aligned. No batteries, no calibration, no electronics. It works every time, forever. At under $30, it is the highest-value accessory you can buy for a reflector telescope.

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Collimation Maintenance Tips for Long-Term Success

Good collimation habits extend beyond the initial setup. Here are practical maintenance practices that keep your reflector performing at its best over months and years of use.

Check collimation at the start of every session. Even if the telescope has not moved, thermal expansion from temperature changes can subtly shift mirror alignment. A 30-second laser check before observing prevents an entire evening of soft views. Make it part of your routine, like focusing the finder scope.

Transport triggers re-collimation. Any time you drive with the telescope, assume collimation has shifted. Dobsonian mirrors can shift during even gentle car rides. Budget 5 minutes for a full collimation check when you arrive at your observing site. This is normal, not a sign of poor equipment.

Mark your adjustment knobs. Once you achieve perfect collimation (verified by a star test), mark the position of your primary mirror adjustment knobs with a permanent marker or a small piece of tape. If collimation slips during transport, you can return to the marked position quickly and then fine-tune. This is a time-saving trick used by experienced Dobsonian owners.

Upgrade your adjustment knobs. Many Dobsonians come with small plastic knobs that are hard to turn in the dark. Replacing them with larger aluminum thumbscrew knobs (available for under $15) makes collimation adjustments significantly easier, especially when wearing gloves in cold weather. Bob's Knobs is the most popular aftermarket brand for this upgrade.

Troubleshooting Common Collimation Problems

If you are still having trouble after multiple attempts, check that your telescope's primary mirror is properly cooled to ambient temperature. Thermal currents inside the tube can mimic collimation errors at high power. Allow 30–60 minutes for the telescope to cool down before precision collimation.

FAQ: Laser Collimator and Telescope Collimation

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