William Optics Apochromatic refractor AP 81/478 GranTurismo 81WIFD OTA (77771)

At a glance:

• New design with integrated focuser

• Premium optics for astrophotography

• Supports heavy, full-frame cameras

• Incorporates key features from the WO "Red Cat" series

William Optics’ GranTurismo refractors are renowned for their FPL-53 glass, offering exceptional color accuracy and high contrast. This versatile apochromatic refractor meets the demands of both visual astronomers and astrophotographers.

Visual Observation:
With an optional diagonal mirror, the GT81 provides high-contrast views of the Moon and planets. Its fast optics allow for extended observation of challenging deep-sky objects—star clusters, galaxies, and nebulae—all with crisp, pinpoint stars, making globular cluster observation especially rewarding.

Astrophotography:
For imaging, the Flat6AIII field flattener/reducer from William Optics is recommended. The triplet optics produce a flat field with a constant focus position, perfect for full-frame cameras. The integrated prism rail in the handle lets you add a guiding scope for either finding or guiding during imaging sessions.

WIFD: Innovative Internal Focuser
The latest GT81 introduces the “WILLIAM OPTICS Internal Focus Design” (WIFD)—a patented internal focusing system integrated within the main tube. This advanced mechanism keeps all focusing movements inside the tube, offering superior precision and preventing external misalignment or exposure to the elements. The WIFD is specifically engineered to handle even the heaviest cooled cameras, making it ideal for uncompromising astrophotography.

With this design, you get the benefits of a dual fine-focusing system without the typical limitations of rear-mounted focusers, such as vignetting. A convenient position indicator window on the focuser shows the exact focusing position at a glance.

Inspired by the success of the "CAT" astrograph series, the GT81 WIFD carries over their best astrophotography features. The robust tube has no restrictions on the weight of photographic accessories. The improved “CAT” tube rings and dovetail base are lighter, yet just as sturdy, allowing for better balance when using heavy gear. The signature William Optics carrying handle is included.

The built-in field rotator allows for smooth camera rotation with degree markings and a knurled locking screw to secure your framing.

Travel-Ready and Reliable
The durable GranTurismo Apo is perfect for travel and mobile use, whether for visual astronomy or astrophotography. Take it under dark skies and enjoy the highlights of the Messier and NGC catalogs. The scope is stable, easy to use, and may quickly become your favorite after just one night out.

Note: The flattener and guidescope shown in some images are not included. For flattening, see item 62653, “Adjustable Flattener Flat6AIII.”

Specifications

Optics

• Type: Refractor (Apochromat, Triplet lens)

• Aperture: 81 mm

• Focal Length: 478 mm

• Focal Ratio: f/5.9

• Resolving Power: 1.70 arcseconds

• Limiting Magnitude: 11.3

• Light Gathering Power: 130× the naked eye

• Maximum Useful Magnification: 162×

Mechanical

• Tube Weight: 3.9 kg

• Carrying Length: 390 mm

• Tube Length: 460 mm

• Coating: SMC multi-coating

• Stray Light Baffles: Yes

Focuser

• Type: Internal helical, integrated in the tube (WIFD)

• Eyepiece Connection: 2" RotoLock

• Free Aperture: 64 mm

• Motorized: No

• Ring Clamp: Yes

• Fine Focusing: 1:10 gear reduction

• Connecting Thread (Telescope Side): M92 / M63

Mount

• Type: OTA (Optical Tube Assembly only; no mount included)

Included Accessories

• Finder Scope: Not included

• Dew Shield: Yes

• Diagonal: Not included

• Prism Rail: Vixen-style

• Bahtinov Focus Mask: Yes

• Carrying Handle: Yes

• Carry Case: Yes

General

• Series: Gran Turismo

• Color: Red

Recommended Uses

• Astrophotography: Yes (excellent)

• Moon & Planets: Yes

• Nature Observation: No

• Nebulae & Galaxies: Yes

• Solar Observation: No (only with a suitable solar filter)

User Level

• Beginners: No

• Advanced Users: Yes

• Observatories: No