Collimating a Ritchey-Chrétien · Step 3 of 6
Mechanics first
In a sentence: No collimation holds with a sagging focuser, pinching screws or an imaging train that wobbles. Ten minutes of checks save whole nights.
What to check
- The focuser: no play when you push on it with the camera attached. The stock ones sometimes flex; a good adjustment or a better focuser fixes it.
- The imaging train: threaded connections rather than compression rings, and nothing hanging loose.
- The mirror screws: snug, not forced. Overtightened screws pinch the mirror and give you triangular stars.
- Sensor tilt: check it with a tilt analyzer before you collimate.
- Where to collimate: about 70° up, the part of the sky you’ll image. Check first that the collimation holds when you point to different parts of the sky.
- With your working train: the same camera, the same spacers and the focuser roughly where it usually sits at focus. A different train weighs differently and levers differently.
- With a cooled-down tube: if two frames in a row, without touching anything, don’t look alike, the air in the tube is still moving. Wait.
A focuser tilt adapter
On closed tubes, a tilt adapter between the tube and the focuser (TS-Optics and others sell them for these RCs) lets you aim the focuser at the secondary without touching the primary. It doesn’t replace collimation, but it breaks the “I move the primary and my focuser goes crooked” loop. Heads-up: depending on how it’s fitted, it can cover the primary’s screws.
TipA camera tilt plate (ZWO, Gerd Neumann and similar) corrects the sensor, not the mirrors: it’s for tilt, not for collimation.