Sky-Watcher HAC125 DX 125mm f/2 Astrograph optic

HAC125 DX 125mm f/2 Astrograph

The Sky-Watcher HAC125 DX is a fast f/2 astrograph built around a 125mm aperture Honders Advanced Catadioptric design. It targets astrophotographers who want wide-field, deep-sky imaging in a compact tube that measures 15.7 inches long. The optical formula combines reflective and refractive surfaces to deliver diffraction-limited performance across a 16mm image circle. It suits both beginners and advanced imagers seeking a portable, high-speed platform.

Helical primary mirror focuser

A rear helical focuser on the primary mirror replaces the front-cell focus of the original HAC125. This change allows a wider range of cameras to reach focus and makes adjustments smoother while the telescope is aimed. The mechanism supports precise, repeatable focus steps critical for fast optics, removing the need for external focus motors in many setups. It directly improves usability for imaging sessions that demand frequent, fine focus corrections.

16mm image circle and f/2 speed

The 16mm image circle covers sensors such as the IMX533 and IMX585 without vignetting, matching popular one-inch and 1/1.2-inch formats. At f/2 the system gathers data roughly five times faster than an f/4.9 instrument, cutting total exposure time and often eliminating the need for autoguiding. Larger sensors exceeding the 16mm circle will show corner fall-off, and visual observers wanting eyepiece use will find the design optimised purely for imaging. Users needing wider corrected fields or longer focal lengths should consider other configurations.