Vixen A81M AC 81/910 OTA

Description

Operating at a 910mm focal length with 1.43 arcseconds theoretical resolving power, the Vixen A81M AC 81/910 OTA is a Japanese-crafted achromatic doublet refractor optical tube assembly built for lunar surface auditing, planetary observation, and double-star astrometry. Sized with an unobstructed 81mm (3.19 in) clear aperture and an f/11.2 focal ratio, this telescope gathers light to visual magnitude 11.3, resolving subtle crater details on the Moon and splitting close binary star pairs.

The optical system features an air-spaced long-focus Fraunhofer doublet objective fabricated from high-grade Japanese precision annealed crown and flint optical glass, treated with fully multi-coated (FMC) broad-band anti-reflection optics and an unobstructed 0% central profile. Built inside an aluminum chassis measuring 890mm in length with a 90mm outer tube diameter, the tube assembly supplies 145mm of back focus from the rear visual back without a diagonal. Supported by a 2-inch dual-knob rack-and-pinion focuser with mechanical tension adjustment and a direct SLR T-thread interface, this 3.50 kg (7.72 lbs) refractor illuminates a 44mm full-frame image circle for visual observing and telephoto imaging.

Key Features of Vixen A81M AC 81/910 OTA

Engineered for high-contrast planetary and lunar observation, this Japanese-made 81mm refractor combines long-focus optics with an integrated dual-port flip mirror diagonal. Its heavy-duty tube mounting rings, top metal carrying handle, and standard Vixen dovetail plate ensure mechanical stability on equatorial or alt-azimuth mounts.

• 81mm (3.19 in) clear aperture with 910mm focal length and high-contrast f/11.2 optical speed
• Air-spaced Fraunhofer doublet made from Japanese precision annealed crown and flint glass
• Fully multi-coated broad-band anti-reflection optics delivering high light transmission
• 2-inch rack-and-pinion focuser with tension adjustment and integrated SLR T-thread coupling
• Generous 145mm back focus distance measured directly from the rear visual back
• Corrected 44mm full-frame image circle covering visual eyepieces and camera sensors
• Tube mounting rings with standard 44mm Vixen-style dovetail plate and metal carrying handle
• Dual-port flip mirror diagonal and red dot finderscope included in the factory package

Precision Annealed Japanese 81mm Doublet Train

The long f/11.2 optical configuration minimizes secondary spectrum chromatic aberration inherent to Fraunhofer doublets without requiring complex optical cells. Annealed Japanese optical glasses maintain precise wavefront curvature across nocturnal temperature shifts, supporting practical visual magnifications from 11.6x up to 162x.

Dual-Port Flip Mirror Mechanism & 2-Inch Drawtube Drive

Focusing precision is handled by a 2-inch rack-and-pinion drawtube equipped with dual focus knobs and an adjustable tension brake to prevent drawtube slip under accessory loads. The included dual-port flip mirror diagonal allows observers to toggle instantly between a 1.25-inch visual eyepiece and a straight-through camera port threaded for T-rings, while the 3.50 kg assembly balances smoothly via its top handle.

• 2-inch rack-and-pinion focuser with mechanical tension adjustment to prevent accessory creep
• Integrated dual-port flip mirror diagonal for instant switching between eyepiece and camera
• Heavy-duty aluminum tube rings with top carrying handle for balanced mount transport

Vixen Made-in-Japan Achromatic Series Guarantee

The Vixen A81M AC 81/910 OTA is backed by a 5-year limited warranty against material and manufacturing defects. The complete factory package contains the A81M optical tube, tube mounting rings, Vixen dovetail plate, top carrying handle, red dot finder, and a dual-port flip mirror diagonal.