Celestron 93648 Off-Axis Guider 12.5 mm prism

Celestron 93648 Off-Axis Guider

The Celestron 93648 Off-Axis Guider is an astrophotography accessory designed for long focal length telescopes. It uses a prism to intercept a small portion of the focal plane for precise guiding. This ensures guide star movement matches the imaging camera for round stars. The unit is crafted from durable black anodized aluminum.

Integrating the guider into an imaging train

The guider fits into a standard astrophotography setup requiring a telescope, imaging camera, and autoguider camera. Its compact design allows it to sit close to the focal plane without excessive back focus consumption. The fixed-orientation helical focuser provides smooth, precise focusing for the autoguider. The adjustable 12.5 mm prism can move closer to the center to capture brighter guide stars.

Upgrading from separate guide scopes

This off-axis guider replaces the need for a separate guide scope mounted alongside the main telescope. It eliminates differential flexure between two optical tubes for improved tracking accuracy. The jump is worth it when imaging at long focal lengths where flexure becomes problematic. It is not suited for wide-field setups using short focal length refractors.