Explore Scientific Rack and Pinion Focuser 2.5" Extension Tube

This tube adds 2 inches of outward travel to your focuser. It's designed for situations where your camera or accessory combination (like a DSLR with a T-ring, or a CCD with a filter wheel) requires more back focus than your telescope's focuser can provide on its own.

It is specifically designed for the Explore Scientific 2.5-inch hexagonal rack and pinion focuser. It is machined to seamlessly thread onto this focuser body, maintaining the system's rigidity and alignment.

You would need this extension if you cannot achieve focus because your focuser is racked all the way out. This is a common scenario when imaging the Moon with a DSLR through an Explore Scientific ED series refractor, or when using an accessory stack with a long light path.

While any extension can potentially introduce flexure, this tube is engineered to minimize it. By matching the 2.5-inch hexagonal design of the Explore Scientific focuser, it provides a more rigid and stable connection than a standard round extension tube would, helping to prevent tilt even with heavier cameras.

Installation is straightforward. You typically unthread the 2-inch eyepiece holder from your focuser drawtube, thread the 2.5-inch extension tube in its place, and then reattach your eyepiece holder or camera adapter to the end of the extension tube.

Yes, this is a primary use case. Field flatteners and reducers have specific back focus requirements (e.g., 55mm from the sensor). This 2-inch (50.8mm) extension tube provides the bulk of the required distance, allowing you to use fine-tuning spacers to hit the precise back focus for a perfectly flat field.