William Optics Gran Turismo GT 71 AP 71/420 OTA

Description

Packing down to 325mm for dark-sky expeditions and airline travel, the William Optics Gran Turismo GT 71 AP 71/420 OTA is an ultra-portable apochromatic triplet refractor optical tube assembly. Operating at an f/5.9 focal ratio with a 420mm focal length, this 71mm (2.80 in) clear aperture instrument delivers a 1.63 arcseconds theoretical resolving power and reaches magnitude 12.0, collecting photons across extended emission nebulae, open clusters, and rich Milky Way star fields.

The optical system features an air-spaced Super APO triplet objective mounted in a CNC temperature-compensated lens cell, incorporating an FPL-53 Super ED center element paired with lanthanum mating glasses, treated with ultra-high transmission broad-band multi-coatings (STM) with an unobstructed 0% central profile. Built inside an aluminum chassis measuring 325mm retracted and 380mm extended with a 92mm outer dew shield diameter, the tube assembly supplies 140mm of back focus from the rear mechanical thread (55mm standard from M48 threads on optional Flat6AIII reducers). Supported by a 2.5-inch dual-speed rack-and-pinion focuser with an integrated 360-degree field rotator and a precision thermometer, this 2.20 kg (4.85 lbs) refractor illuminates a 44mm full-frame flat field with dedicated correctors.

Key Features of William Optics Gran Turismo GT 71 AP 71/420 OTA

Built for mobile astrophotographers seeking high optical performance in a compact footprint, this 71mm triplet pairs certified FPL-53 optics with a 2.5-inch rack-and-pinion focuser. CNC-machined split tube rings, a reversible Vixen and Arca-Swiss dovetail bar, a top saddle handle with a guiding bracket slot, and an integrated Bahtinov mask cap provide an adaptable field platform.

• 71mm (2.80 in) clear aperture with 420mm focal length and fast f/5.9 optical speed
• Air-spaced Super APO triplet objective with FPL-53 Super ED and lanthanum mating elements
• Ultra-high transmission broadband multi-coatings with certified Strehl ratio of 0.95 or greater
• 2.5-inch dual-speed rack-and-pinion focuser 1:10 with built-in 360-degree field rotator and thermometer
• Generous 140mm back focus distance from mechanical thread (55mm from M48 thread on Flat6AIII)
• Corrected 44mm full-frame flat field image circle when paired with dedicated Flat6AIII reducer
• Reversible Vixen/Arca-Swiss dovetail bar with CNC tube rings and top saddle handle
• Patented clear Bahtinov focus mask cap and top saddle handle with finder slot included in package

Ultra-Compact FPL-53 Triplet Glass & Wide-Field Coverage

The air-spaced triplet lens cell pairs an FPL-53 Super ED center element with high-index lanthanum glass inside a temperature-compensated cell, canceling secondary spectrum chromatic aberration across broad bandwidths. Supported by an interferometer-certified Strehl ratio of 0.95 or higher, the unobstructed 71mm optical path delivers high contrast, supporting practical visual magnifications from 10.1x up to 142x.

Precision Thermometer Dial & Dual-Format Dovetail Bar

Holding cooled astronomy cameras without drawtube flexure is delivered through a 2.5-inch rack-and-pinion focuser with a 1:10 micro-reduction gear, an integrated 360-degree camera field rotator, and an embedded thermometer to track ambient temperature shifts. Weighing just 2.20 kg with rings, handle, and dovetail, this compact optical assembly mounts effortlessly on travel tracker saddles.

• 2.5-inch dual-speed rack-and-pinion focuser with 1:10 micro-reduction and integrated temperature gauge
• Built-in 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 Gran Turismo Travel Series Warranty

The William Optics Gran Turismo GT 71 AP 71/420 OTA is backed by a 2-year limited warranty against material and manufacturing defects. The complete factory package contains the GT71 Triplet OTA, integrated patented Bahtinov focus mask cap, CNC tube rings, dual-sided dovetail bar, and a top saddle handle with finder/guide slot.