William Optics GT81 81mm f/5.9 Apo Refractor with Soft Case - Available in three colors # A-F81GTIV

Latest Gen IV version introduced in June 2020

Innovative Bahtinov Mask Cover (Patented), New Dovetail Plate and Built-In Camera Angle Rotator included!

Air-Spaced Triplet f/5.9 Apochromatic Refractor 

The new William Optics GT81 three-element super APO offers superb optics for imaging and visual use at an affordable price. From the gleaming white powder coat on the heavy-duty aluminum tube to the elegant color trim, this telescope is beautiful enough to turn heads and precisely engineered to give razor-sharp images.

The fast f/5.9 triplet air-spaced objective of this premium refractor includes FPL-53 glass for superb color correction. Each element is fully multicoated with a special super-high transmission (STM) coating on all surfaces. The objective is held in an adjustable CNC machined ultra-high precision lens cell. When paired with a William Optics field flattener (sold separately), the scope delivers a flat field across the entire 43.3mm diagonal of a full-frame sensor for excellent astrophotographic images.

Premium Build Quality and Compact Form Factor

Like all telescopes from William Optics, the GT81 incorporates rock-solid mechanics and built quality. The scope includes high-quality mounting rings to safely and securely hold the telescope to the mount. The rings are anodized to match the color of the handle, dovetail, and focuser, giving the scope an attractive, premium appearance. 

With a focal length of 478mm, this f/5.9 telescope has a retracted length of just 390mm (15.4”), compact enough to qualify as carry-on luggage with most airlines. The tube weighs just 3.9kg (8.6lbs) including tube rings and dovetail plate.

Heavy-Duty Focuser with Integrated Camera Rotator, Tube Rings, Soft Case and Accessories

The William Optics GT81 features a patented objective lens cover that doubles as clear Bahtinov focusing mask. This makes it a snap to achieve sharp focus when setting up for astrophotography.

The GT81 also features a heavy duty 10:1 dual-speed 2.5” rack and pinion focuser with tension screws to securely hold a bigger camera and accessories without slipping or image shift, even during longer exposures. The coarse-focus knob includes a thermometer to help you track temperature changes during your observation sessions so you know when you may need to adjust focus. The focuser dratube terminates in a 2" holder and also comes with a 1.25”-2” adapter with non-marring compression rings. The focuser also includes two additional screws to mount a red-dot finder (sold separately).

This Gen IV version now incorporates a built-in camera angle adjuster (rotator) within the drawtube assembly with full 360-degree camera orientation control.

A convenient CNC-machined carrying handle mounts on top of the dual mounting rings. A dovetail in the handle accommodates William Optics' Uniguide guidescopes or an additional set of rings for a conventional guide scope (guide scope rings and guide scope sold separately). On the bottom of the mounting rings is a reversible dovetail with a Vixen rail on one side and an Arca Swiss mount on the other for mounting the scope to a camera tripod for grab-and-go terrestrial and astronomical observation. The GT81 also includes a retractable dewshield, dewshield cap, and soft carry case.

Specifications:

• Focal Length: 478mm
• Diameter: 81mm
• Aperture: f/5.9
• Camera Format: APS-C, Full Frame
• Focuser: 2.5" R&P Focuser
• Image Circle: >Full Frame (with recommended flatteners; image circle size without a flattener will be smaller but has not been specified by William Optics)
• Recommended Flattener: Flat6AIII
• Tube Length (Fully Retracted): 390mm
• Tube Length (Fully Extended): 460mm
• Dew shield OD: 103mm / 4.05"
• Tube Weight: 3.9kg
• Interchangeable T-Mount (sold separately): Canon EF, Nikon F, Sony E, Pentax, Micro Four Thirds, Fuji FX

All GT81 telescopes come with a 2-year no-fuss warranty from William Optics.

Specifications for William Optics Apo Lenses

All William Optics refractor objectives are double tested and inspected by WO at their factory. These telescopes are free of coma and astigmatism. Since all individual lens surfaces are machine coated, sometimes you may notice minor visual imperfections which will not compromise the optical performance of the telescope. The dimensions of scratches and points shall not exceed the following values:

• Scratches - Maximum Width: 0.025 mm
• Scratches - Maximum Length: 1/4 of total lens diameter
• Scratches - Maximum Quantity: Three
• Dots or Spot Points - Maximum Diameter: 0.4 mm
• Dots or Spot Points - Maximum Quantity: Three
• Accumulation of Defects - Limited Area: 0.8mm^2
• Accumulation of Defects - Total Area: 5.8mm^2