William Optics GT-81 Triplet Refractor

SkySlab has used this little beautiful refractor for a few photos in 2013 but is currently taking closer field of view shots of objects rather than wide field of view shots. The WO-GT81 will produce stunning wide-field shots, is very fast in terms of light gathering and has no negative coma or chroma effects. They were individually numbered, only 150 made world wide. SkySlab used number 33. This is the holy grail in 81mm triplets.

At a Glance:

  • Aperture: 81mm
  • Focal Ratio: f/5.9
  • Focal Length: 478mm
  • Objective: Air-spaced triplet using FPL-53 coated glass
  • Focuser: 2.5″ 2-speed Crayford Focuser with DDG digital readout
  • 2″-fit 360-degree camera-angle adjuster
  • 2″ to 1.25″ eyepiece adapter with anti-marking brass insert
  • Focus Travel: 80mm
  • Weight: 2.9kg
  • Length with dew shield retracted: 340mm
  • Length with dew shoeld extended: 400mm
  • Includes Carry Handle and rigid high-quality backpack with custom-fitted foam
  • Backpack dimensions: approx 44cm x 30cm x 17cm (Water resistant)
  • Backpack weight: 1.8kg

Optically Unbeatable

Triplet air-spaced objective (FPL-53) in adjustable CNC machined ultra high precision lens cell. Extremely sharp. Excellent colour correction. Each lens is Fully Multi-Coated with a special super-high transmission coating (STM Coating) on all surfaces.

This F/5.9 lens is ideal for astrophotography.

2.5” DDG Focuser

The Digital Display Gauge – DDG – allows you to take precise focusing readings to two decimal places. Extra-smooth 360 deg. rotatable 2.5″ Crayford focuser with 1:10 dual speed: a treat to use during astrophotography. No image shifting.

Comes with two locking screws for heavy loads. Large aluminum knob with installed thermometer.

Patented Design

Stainless steel reinforcement inserts on both sides and on the back to allow heavy loading without problems. DDG integration will make your focusing experience the best ever.

Graduated scale for precise camera alignment.

Simply Beautiful Finish

Pure William Optics quality fit and finish: powder-coated white CNC-machined aluminum tube, dark red finish, retractable dewshield, 360 deg. rotatable PowerLinear focuser, dewshield cap. Top quality anodizing. Very compact for carrying on flights.

Attention to Detail

2″ & 1.25″ adapter included with the scope.
Carry handle with V-shape night glowing illuminator.

SkySlab used a William Optics P-Flat-81 which is an additional field flattener specifically designed for the GT-81, two William Optics anti-marking compression rings, a William Optics DB15 DuraBright coated carbon-fibre viewing 90 degree angle and a losmandy style small mounting plate for mounting to the Paramount MX robotic mount.

You can see photos here of the scope that was used. It was a delight to work with.  I used a JMI motorised focuser specifically designed for the William Optics DDG2 focuser. By combining the motorised focuser with the DDG already attached to the WO-GT81, imaging sessions could be run remotely using the WO-GT81 and some stunning images were captured including the image of NGC3372 (Eta Carinae Nebula) in this post below.