William Optics RedCat 71 AP 71/350 OTA

Description

Corrected internally to illuminate a flat 45mm sensor circle without external flatteners, the William Optics RedCat 71 AP 71/350 OTA is a dedicated full-frame petzval flat-field apochromat optical tube assembly. Operating at an f/4.9 optical speed with a 350mm focal length, this 71mm (2.80 in) clear aperture telescope delivers a 1.63 arcseconds theoretical resolving power and reaches magnitude 11.9, collecting photons rapidly across faint extended nebulae and wide deep-sky survey fields.

The optical system features a modified Petzval quadruplet design combining a doublet front objective with a doublet rear field corrector, incorporating Ohara FPL-53 Super ED glass and synthetic fluorite elements, treated with ultra-high transmission broad-band multi-coatings with an unobstructed 0% central profile. Built inside an aluminum chassis measuring 310mm in retracted length with a 103mm outer dew shield diameter, the tube assembly supplies exactly 55mm of standard back focus from the rear M48x0.75 male camera thread. Supported by an internal precision calibrated helical focuser with an integrated 360-degree camera rotator, this 2.80 kg (6.17 lbs) astrograph maintains a diffraction-limited 45mm full-frame flat field from edge to edge.

Key Features of William Optics RedCat 71 AP 71/350 OTA

Built for mobile deep-sky astrophotography on portable tracking mounts, this 71mm flat-field astrograph pairs an internal focusing mechanism with certified fluorite optics. Its CNC mounting rings, top saddle handle, reversible Vixen and Arca-Swiss dovetail bar, and custom soft padded case provide a rigid, travel-ready imaging system.

• 71mm (2.80 in) clear aperture with 350mm focal length and fast f/4.9 optical speed
• Petzval-style quadruplet design with Ohara FPL-53 and synthetic fluorite optical elements
• Ultra-high transmission broadband multi-coatings with an unobstructed 0% central profile
• Internal precision calibrated helical focusing mechanism with 360-degree camera rotator
• Standard 55mm back focus distance measured directly from the rear M48x0.75 male thread
• Corrected 45mm full-frame edge-to-edge flat field without requiring auxiliary correctors
• Reversible Vixen/Arca-Swiss dovetail bar with CNC mounting rings and top saddle handle
• Patented clear Bahtinov focus mask cap, M48 thread adapter, and soft padded case included

Self-Contained Flat-Field Optics & 45mm Image Circle

The self-contained four-element Petzval design cancels secondary spectrum chromatic aberration, spherical aberration, and field curvature natively without supplementary optical elements. The 45mm image circle illuminates full-frame camera sensors with zero vignetting, while the unobstructed 71mm aperture supports practical visual magnifications from 10.1x up to 142x.

Internal Focusing WIFD Mechanics & Field Rotator

Focusing precision is delivered through an internal helical focusing system that shifts internal optical elements rather than extending an external drawtube, completely preventing camera tilt and mechanical drawtube flexure. A smooth 360-degree field rotator facilitates photographic framing, while the 2.80 kg optical assembly mounts securely via its dual-profile dovetail bar.

• Internal helical focusing mechanism eliminating external drawtube sag under heavy camera loads
• Integrated 360-degree camera field rotator for rapid target orientation without losing focus
• Patented clear Bahtinov focus mask integrated into the metal lens cap for precise focus acquisition

William Optics Cat Series Factory Protection

The William Optics RedCat 71 AP 71/350 OTA is backed by a 2-year limited warranty against material and manufacturing defects. The complete factory package contains the RedCat 71 OTA, integrated patented Bahtinov focus mask cap, CNC mounting rings, dual-sided dovetail bar, top saddle handle, M48 camera thread adapter, and a soft padded case.