William Optics GT-81 IV - Checked & Tuned

  (2 Reviews)
✓ 2 year warranty


4x in stock shipped 1-2 working days

About this product

Model:  wo_gt81_iii_tg
Part Number:  A-F81GTIVTG

New upgraded 2020 model with 2.5" R&P focuser and Camera Angle Rotator. 

Price includes a pre-dispatch optical bench test. 

Optical Bench Test

FLO tests all William Optics triplet refractor telescopes before dispatch. 

You can be confident your telescope will, from the outset, have well figured optics, negligible false colour and spherical aberration, and no astigmatism (the bane of any optical system!).

Star shapes will be round, not triangular, oval or egg-shaped!

The William Optics GT-81 APO Triplet refractor features a 3-element f/5.9 objective with an Ohara FPL-53 extra-low-dispersion glass element for optimum colour correction and a new upgraded dual-speed 2-inch Rack and Pinion focuser with 1:10 Dual Speed. 

The William Optics 0.8x focal reducer is also available to reduce the focal-ratio to a fast f4.72. 

An excellent choice for astrophotography!

Includes tube rings, carry handle/guider mounting saddle.

(Photo shows earlier model)


    Superb Optics

  • Triplet air-spaced objective (FPL-53) in adjustable CNC machined ultra high precision lens cell.
  • Extremely sharp.
  • Excellent color 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.
  • New ultra robust 2.5" Rack and Pinion focuser with 1:10 dual speed: a treat to use during astrophotography. No image shifting.

    Simply Beautiful Finish

  • Pure William Optics quality fit and finish: powder-painted white CNC-machined Aluminium tube, gold/red or blue trim finish, retractable dewshield, dewshield cap with patented Bahtinov mask.
  • Top quality anodising.
  • Very compact for carrying on flights.

    Attention to Details

  • 2" & 1.25" adapter included in the price.
  • Anti-marring brass compression rings.
  • Though you will never need it, you have a 2-year warranty from WO, and the certainty that we will be there to assist you even beyond that, if you need!

What's in the box

  • Telescope OTA
  • Vixen compatible dovetail plate
  • Carry Handle
  • Bahtinov Mask
  • 2" to 1.25" Adapter
  • Soft Carry Bag


Focal RatioF/5.9
Focal Length478mm
Resolving Power1.43"
Limiting Magnitude12.2
Objective TypeThree element with FPL-53 Air Spaced, Fully Multi-Coated,STM coatings
Lens ShadeRetractable
2.5" Rack and Pinion Focuser1:10 fine focus
1.25" Adapter
Field StopsKnife-Edge Baffles
L-type MountBracket
Tube Diameter90mm
Tube Length(390 mm) Fully Retracted
Tube Weight3.95kg

Customer reviews

Average Rating (2 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
Pin-point stars everywhere
Saturday, 21 August 2021  | 

This is a superb piece of triplet, with medium reach. Great scope for most of the nebulas and few of the galaxies. With the flattener, the stars are round corner to corner. Luckily, I got the red one, which nicely matches with ZWO environment and GEM28. As usual, all the advice given by Alex prior to purchase regarding backfocus, attaching the camera and so on. 5 stars for the scope and FLO. I would give 6 for Alex. Cheers.

Rating (max 5):  
Excellent service
Saturday, 3 October 2020  | 

Five stars for both the telescope and the service! The GT81 is absolutely fantastic for astrophotography and has the great quality associated with WO gear. Purchasing through FLO gives peace of mind having had the Es Reid optical check and FLO’s service was great as they kept me updated on how the order was progressing and answered queries I had.


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