Focus Scientific

Antares Cheshire Eyepiece/Sight Tube Combo Collimation Tool (1.25\")

Collimating Newtonian reflector telescopes can be a daunting task, but it is crucial to achieving good performance, especially for those instruments with fast focal ratios (eg., f/5 and less).

This tool is a combination Cheshire eyepiece and sight tube. It allows for precise alignment of both the primary and secondary mirrors. It fits standard 1.25" focusers, and can be used with an optional 2" reducer adapter (2" reducer adapter sold separately).

Step One - Secondary Mirror Alignment - The sight tube portion of this tool helps you centre the secondary mirror under the focuser. The built-in crosshairs help you align the secondary mirror's projected axis of symmetry to the centre of the primary mirror.

Step Two - Primary Mirror Alignment - The Cheshire eyepiece portion has a metallic, 45° reflective window which helps you align the primary mirror to the crosshair.

Step Three - Collimation on a Star - A final star collimation should be performed to weed out any residual error. For telescopes that don't track, use Polaris because it barely moves.

Aren't Laser Collimators Better? - Not necessarily. Particularly if one has not verified that the secondary is properly positioned under the focuser (which the Cheshire device does.) It's difficult to make adjustments so that the laser hits the centre of the secondary and primary mirrors simultaneously, especially considering most reflectors don't allow for direct observation of the secondary mirror reflective surface - most astronomers simply guess. Experts advise customers using laser collimators to place a centre mark on their secondary mirrors, and over the last 17 years, we've only seen a small handful of customers willing to do this.

Laser collimators with a side-viewing inspection window are useful when collimating primary mirrors, especially of longer focal length instruments, because you can see your adjustments in real-time. Follow it up with the Cheshire to refine your alignment.