Explore Scientific 3-inch Self-Centering Focuser

A precision 3-inch rack-and-pinion focuser with a self-centering compression system, 9:1 reduction ratio, and 17-pound lifting capacity — built for astrophotographers who need rock-solid focus with heavy imaging trains.

The self-centering compression ring applies uniform pressure around the entire circumference of the drawtube, eliminating the tilt and image shift that single-setscrew focusers introduce. The helical rack-and-pinion mechanism with a 9:1 reduction ratio turns coarse motion into fine, precise control — critical when focusing at long focal lengths with a camera. Stainless steel ball bearings ensure smooth travel across the full 84.5mm of drawtube movement. A locking clutch holds focus without disturbing the image.

Fourteen internal baffles suppress stray light and internal reflections, keeping contrast high for both imaging and visual use. The entire assembly is machined from black anodized aluminum with stainless steel hardware — no plastic anywhere in the load path.

The focuser accepts 2-inch and 3-inch accessories via M82 x 1.25 threads. Tool-free adjustment knobs set tension to match your equipment weight. The design is compatible with electric focuser motors for automated focusing.

Three configurations available:

• ES-FOC3 — Focuser only, for Explore Scientific 152mm and 165mm refractors
• ES-FOC3-BC100127 — Focuser with back cell adapter for the FCD100-127-CF (carbon fiber tube)
• ES-FOC3-BC100127T — Focuser with back cell adapter for the white tube ED127 and FCD-100 series

Key Features

• Self-centering compression system — zero tilt, zero image shift
• 9:1 helical rack-and-pinion with stainless steel ball bearings
• 17 lb lifting capacity — supports heavy imaging trains
• 84.5mm (3.32") drawtube travel
• 14 internal baffles for stray light suppression
• M82 x 1.25 thread for 2" and 3" accessories
• Locking clutch and tool-free tension adjustment
• Electric focuser motor compatible

Ideal For

• Astrophotographers with heavy imaging trains — 17 lb capacity handles cameras, filter wheels, and off-axis guiders without flex
• Owners of Explore Scientific 120mm+ refractors — direct-fit upgrade from the stock focuser
• Visual observers who want the best focus precision — the 9:1 ratio makes fine focus effortless at high magnification