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Australia's best William Optics & Explore Scientific distributor with local stock
Australia's best William Optics & Explore Scientific distributor with local stock

William Optics GT81 WIFD Apochromatic Refractor

Original price $3,599.00 - Original price $3,599.00
Original price $3,599.00
$3,599.00 - $3,599.00
Current price $3,599.00
Color: Red

Introducing the WILLIAM OPTICS Internal Focus Design (WIFD) Apochromatic Series. This innovative and revolutionary design combines a precision (Patented) internal focusing mechanism with the highest quality optics available, providing the ultimate Apochromatic refractor for astrophotography.

Designed from the ground up with the ability to handle the newest generation of large, heavy, high-resolution cooled cameras, the rock-solid optical tube assembly is uncompromised in quality.

The movement of the focuser is integrated inside the main tube assembly, so there are no movements of a focuser drawtube visible from the outside.  The user can enjoy the benefits of a traditional two speed fine focuser, while not worrying about limitations typically found in traditional rear mounted focusers.  

Add FLAT68III extension (for imaging) here
Add Rotolock (for visual use) here


NEW internal focuser.  This new telescope includes the Patented centre focuser with precise internal sliding of fixed optics to prevent image shift. The integrated viewing window on the focuser has a useful graduated numerical display. The smooth rack and pinion mechanism integrated into the focuser enables super-fine focus adjustment. The design's redistribution of weight provides better balance during imaging sessions. Also, the telescope's optics are more protected from the environment and less likely to move out of alignment. 

Scalable Design.  The WIFD series is not limited to smaller refractors. With its inherent benefits, the design can be applied to telescopes with various apertures and fast focal ratios. Other WIFD telescopes are planned. 

Inspired by the success of their CAT series of astrograph telescopes, William Optics have adopted a 'no weight limit on photo accessories' approach to telescope design. The solid tube has a rigid structure, so it does not flex or exhibit any change in the optical path, regardless of the weight of the camera and filter wheel attached.

Improved “CAT” design.  Tube-rings and the dovetail base are made lighter, without sacrificing rigidity. The design enables better balance with heavy accessories and has integral placement of the focuser knobs for easy access during imaging. William Optics' Saddle Bar Handle is included for rigid guidescope mounting and autoguiding performance.

Super Smooth Field Rotator.  The field rotator design features smooth camera rotation with markings for degrees and a locking thumbscrew to prevent accidental camera movement. A new optional Electric Rotator will be available shortly.


Lens Type Triplet Apochromatic Prime Lens
Focal Length 478mm
Diameter 81mm
F/Ratio F5.9
Optional Flattener FLAT6AIII 0.8x,FLAT68III 1.0X (Requires WIFD Extension Adapter)
Focuser WIFD (Compatible with EAF)
Colour Red
Lens Material FPL53
Strehl Ratio 0.95+
Camera Format DSLR,Full Frame,Mirrorless, CMOS,CCD
Optical test Report Included
T Mounts Supported Canon RF,EF,Nikon F,Z,Sony E, Pentax K,M4/3,Fuji X
OTA Weight 7.3 lbs (3.3 kg)
Total Weight 9.9 lbs (4.5 kgs)
Tube Length (retracted) 420mm
Tube Length (Extended) 500mm