William Optics GT81 81mm f/5.9 Apo Refractor - 20th Anniversary Edition - Gold
This item is discontinued by the manufacturer and is no longer available.
Stock count is accurate & shown in real time.
- This item is out of stock.
- Sign up for back-in-stock alerts to be notified when this item becomes available (account login required).
- This item is out of stock.
- Sign up for back-in-stock alerts to be notified when this item becomes available (account login required).
The GT81 20th Anniversary Edition includes a FREE soft carry case.
The new 2016 GT81 three-element super APO Anniversary Edition offers superb quality for imaging and visual use at an affordable price. From the pristine white finish on the CNC to the elegant gold trim which has more than just good looks...
Optically Unbeatable
- Triplet air-spaced objective (FPL-53) in adjustable CNC machined ultra high precision lens cell.
- Extremely sharp with 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.
2" Crayford V-Power Focuser
- New ultra smooth 2" Crayford V-power edition focuser with 1:10 dual speed: a treat to use during astrophotography. No image shifting (capacity 15lb.)!
- Comes with two locking screws on angled positions for heavy load applications.
- Chromed, soft thumbscrews, easy to use even with gloves on.
Patented Design
- Stainless steel reinforcement inserts on both sides and on the back to allow heavy loading without problems.
- Diamond-coated drive system: very smooth, no lateral movement or tilting.
- Graduated scale for precise camera alignment.
Simply Beautiful Finish
- Pure William Optics quality fit and finish: powder-painted white CNC-machined aluminum tube, gold trim finish, retractable dewshield, dewshield cap.
- Top quality anodizing.
- Very compact for carrying on flights.
Attention to Details
- 2" & 1.25" adapter included in the price.
- Anti-marring brass compression rings.
- Carry handle with V-shape night glowing illuminator.
- 2 year warranty from William Optics.
Specification 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
Useful Resources
The GT81 20th Anniversary Edition includes a FREE soft carry case.
The new 2016 GT81 three-element super APO Anniversary Edition offers superb quality for imaging and visual use at an affordable price. From the pristine white finish on the CNC to the elegant gold trim which has more than just good looks...
Optically Unbeatable
- Triplet air-spaced objective (FPL-53) in adjustable CNC machined ultra high precision lens cell.
- Extremely sharp with 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.
2" Crayford V-Power Focuser
- New ultra smooth 2" Crayford V-power edition focuser with 1:10 dual speed: a treat to use during astrophotography. No image shifting (capacity 15lb.)!
- Comes with two locking screws on angled positions for heavy load applications.
- Chromed, soft thumbscrews, easy to use even with gloves on.
Patented Design
- Stainless steel reinforcement inserts on both sides and on the back to allow heavy loading without problems.
- Diamond-coated drive system: very smooth, no lateral movement or tilting.
- Graduated scale for precise camera alignment.
Simply Beautiful Finish
- Pure William Optics quality fit and finish: powder-painted white CNC-machined aluminum tube, gold trim finish, retractable dewshield, dewshield cap.
- Top quality anodizing.
- Very compact for carrying on flights.
Attention to Details
- 2" & 1.25" adapter included in the price.
- Anti-marring brass compression rings.
- Carry handle with V-shape night glowing illuminator.
- 2 year warranty from William Optics.
Specification 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
| Manufacturer | William Optics |
|---|
| Aperture | 81 mm |
| Focal Ratio | F/5.9 |
| Focal Length | 478 mm |
| Objective Type | Three element with FPL-53 Air Spaced, Fully Multi-Coated, STM coatings |
| Resolving Power | 1.43" |
| Limiting Magnitude | 12.2 |
| Lens Shade | Retractable |
| V-Power Focuser | 45mm drawtube 1:10 fine focus 1.25" Adapter |
| L-type Mount | L Bracket |
| Field Stops | Knife-Edge Baffles |
| Tube Diameter | 90mm |
| Tube Length | 440mm Fully Retracted 484mm Fully Extended |
| Tube Weight | 8 lbs. (3.7 kg) |
The GT81 20th Anniversary Edition includes a FREE soft carry case.
The new 2016 GT81 three-element super APO Anniversary Edition offers superb quality for imaging and visual use at an affordable price. From the pristine white finish on the CNC to the elegant gold trim which has more than just good looks...
Optically Unbeatable
- Triplet air-spaced objective (FPL-53) in adjustable CNC machined ultra high precision lens cell.
- Extremely sharp with 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.
2" Crayford V-Power Focuser
- New ultra smooth 2" Crayford V-power edition focuser with 1:10 dual speed: a treat to use during astrophotography. No image shifting (capacity 15lb.)!
- Comes with two locking screws on angled positions for heavy load applications.
- Chromed, soft thumbscrews, easy to use even with gloves on.
Patented Design
- Stainless steel reinforcement inserts on both sides and on the back to allow heavy loading without problems.
- Diamond-coated drive system: very smooth, no lateral movement or tilting.
- Graduated scale for precise camera alignment.
Simply Beautiful Finish
- Pure William Optics quality fit and finish: powder-painted white CNC-machined aluminum tube, gold trim finish, retractable dewshield, dewshield cap.
- Top quality anodizing.
- Very compact for carrying on flights.
Attention to Details
- 2" & 1.25" adapter included in the price.
- Anti-marring brass compression rings.
- Carry handle with V-shape night glowing illuminator.
- 2 year warranty from William Optics.
Specification 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
Useful Resources
| Manufacturer | William Optics |
|---|
| Aperture | 81 mm |
| Focal Ratio | F/5.9 |
| Focal Length | 478 mm |
| Objective Type | Three element with FPL-53 Air Spaced, Fully Multi-Coated, STM coatings |
| Resolving Power | 1.43" |
| Limiting Magnitude | 12.2 |
| Lens Shade | Retractable |
| V-Power Focuser | 45mm drawtube 1:10 fine focus 1.25" Adapter |
| L-type Mount | L Bracket |
| Field Stops | Knife-Edge Baffles |
| Tube Diameter | 90mm |
| Tube Length | 440mm Fully Retracted 484mm Fully Extended |
| Tube Weight | 8 lbs. (3.7 kg) |