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Cyclops Optics

William Optics GT81 81mm f/5.9 Triplet APO Package

Please contact us at for more details

William Optics GT81 81mm f/5.9 Triplet APO Package

Please contact us at for more details
Shipping Weight:
7.00 KGS
Discontinued and succeeded by GT81-II

Product Description

William Optics GT81 APO is a f/5.9 air-spaced triplet FPL-53 apochromat. This package includes a 0.8x Flat6A-81 reducer cum flattener specially designed for GT81 to transform it into a f/4.7 imaging APO covering full frame sensor.


  • GT-81 APO
  • Flat6A-81 reducer flattener 
  • Canon T-mount and spacer 
  • 2" 1:10 rack & pinion focuser
  • 360º camera angle adjuster
  • L-bracket mounting
  • A pair of Finderscope/guidingscope mounting rings
  • 2" to 1.25" adapter with brass compression ring
  • Retractable lens shade
  • Carry handle with V-shape illuminator


  • 81mm f/5.9 triplet air-spaced objectives aprochromatics
  • Includes 1 FPL-53 fluorite element
  • Precision optics with STM coating
  • Very sharp image with great colour correction
  • Designed for astrophotography

Cyclops Optics' Exclusive Fine Tuning Service

We offer fine tuning service for the telescopes to provide a smoother screws control and grant the telescope a premium quality touch. The fine tune service costs HK$400 (US$50). It's now waived for time-limited period.


Optical system Air-spaced triplets with 1 FPL-53 fluorite element
Aperture 81 mm
Focal length 478 mm
Focal ratio f/5.9
Image circle

40 mm

Back focus 64.4 mm with WO Flat6A 0.8x Reducer/Flattener
Resolution 1.43 arcseconds
Limiting magnitude 12.2
Light gathering power 134x
OTA length

400 mm (fully extended)
345 mm (contracted)

Weight 3.1 kg

Free shipping applies

United States, S. Korea, Japan, Malaysia, Philippines, Singapore, Hong Kong, Taiwan, Indonesia, Australia, New Zealand, Germany, France, Switzerland, Sweden, Denmark, Netherlands, United Kingdoms and others.

Via FedEx International Economy. Arriving in 1-5 working days.


7 days no question asked return if due to material or worksmanship defects

2 years from William Optics

Cyclops Optics Ltd. is an authorised dealer of William Optics' products.

Quality Control

Scratches   Width no more than  0.025 mm
 Total length no more than  1/4 of total lens diameter. No more than 3 individual scratches
 Dots or spots   Diameter, no more than  0.4 mm
 Quantity no more than  3
 Accumulation of defects   Limited area  0.8 mm2
 Total area of scratches and points no more than  5.8 mm2







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