The William Optics Cat 51 WIFD 51/250 f/4.9 APO Telescope, Space Grey (SKU: L-RC51SGIII) is a compact apochromatic refractor designed for wide-field astrophotography, including nebulae, star clusters and large areas of the sky. Its four-element Petzval optics work with the WIFD internal focusing mechanism, while the compact dimensions make transport and the assembly of a portable imaging setup easier.
• optical design: Petzval with FPL-53 glass, correcting field curvature without an additional flattener
• internal WIFD focusing: the optics move inside the tube while the camera remains stationary
• dual-speed focusing with a fine-focus control for precise focus adjustment
• integrated camera angle rotator and sensor tilt adjuster
• provision for a 2" filter inside the camera connection adapter
• compatibility with an optional ZWO EAF focus motor
• optical tube in Space Grey with a dew shield, WIFD mechanism, rotator and sensor tilt adjuster
• lens cap with a Bahtinov mask
• adapter: M54–M48 with a 2" filter thread, and a rear dust cap
• tube mounting ring with a carrying handle and Mini Vixen accessory mounting base
• 210 mm dual-sided mounting plate compatible with Vixen and Arca-Swiss standards
• soft carrying case
• hex key set
• optical design: apochromatic refractor with a four-element Petzval system
• low-dispersion glass: FPL-53
• aperture: 51 mm
• focal length: 250 mm
• focal ratio: f/4.9
• image circle diameter: 48 mm
• supported sensor formats: full frame, APS-C and Micro 4/3
• focusing mechanism: WIFD, rack and pinion
• fine-focus reduction ratio: 10:1
• focuser travel: 0–23 mm; scale marked to 30 mm
• camera connection: M48 via the included M54–M48 adapter
• supported filter in the adapter: 2" with an M48 thread
• mounting plate: dual-sided Vixen/Arca-Swiss, 210 mm long
• tube length: 298 mm
• dew shield outer diameter: 84 mm
• optical tube weight: 1.77 kg
• weight with mounting hardware: 2.38 kg
• tube material: CNC-machined aluminium
• colour: Space Grey
The Cat 51 WIFD Space Grey combines optics designed for wide-field astrophotography with precise focusing and equipment that simplifies camera mounting and framing.
