William Optics Gran Turismo GT81 WIFD OTA — 81 mm triplet apochromat This refractor provides a 478 mm focal length at f/5.9. The manufacturer lists a 45 mm image circle and optional correctors for photographic use.
Manufacturer model: William Optics Gran Turismo GT81 WIFD OTA · Specifications checked against manufacturer data on 2026-11-03
William Optics Gran Turismo GT81 WIFD OTA — 81 mm triplet apochromat
This refractor provides a 478 mm focal length at f/5.9. The manufacturer lists a 45 mm image circle and optional correctors for photographic use.
Focusing and camera connection
The WIFD rack and pinion focuser provides 75 mm travel. Connections comprise M92 rotator; M92 to M63 adapter.
Field correction
Manufacturer-listed options: Flat6AIII 0.8x, Flat68III 1.0x, Flat GT 1.0x. Each combination has a specific spacing and adapter arrangement; see the individual settings in the specifications. A corrector is an optional accessory.
Size and weight
Tube length is 420–500 mm and OTA weight is 3.58 kg. Total weight is 4.56 kg.
The objective uses Ohara FPL-53 ED glass for colour correction. The manufacturer lists a dual-sided Vixen / Arca-Swiss dovetail for mounting. For photographic use, select the correct flattener or reducer and its specified adapters; telescope focal length and corrector spacing are separate specifications.
Compatibility notes
Prime-lens telescope: corrector compatibility and spacing are model-specific. Optional correctors are listed, not assumed included; corrector adapters may be required.
Additional specifications
Flat gt with front adapter spacing
55 mm; requires 4-inch OTA extender, removal of 1.6 mm spacer and 30.85 mm flattener front extender
Flat6aiii spacing
62.1 mm backfocus; 7.1 mm adjustment
Flat68iii with back extender spacing
57 mm backfocus; 2 mm adjustment
77771
Technische Daten
Öffnung (mm)
81
Kameraadapter
M92 rotator; M92 to M63 adapter
Kameraformat
Full frame, APS-C and Micro Four Thirds
ED-Glas
Ohara FPL-53
Brennweite (mm)
478
Öffnungsverhältnis
5.9
Auszugsweg (mm)
75
Okularauszugstyp
WIFD rack and pinion
Bildkreis (mm)
45
Vom Hersteller genannte Korrektoren
Flat6AIII 0.8x; Flat68III 1.0x; Flat GT 1.0x
Montageplatte
Vixen / Arca-Swiss dual-sided
Optisches Design
Triplet apochromat
Tubusgewicht (kg)
3.58
Gesamtgewicht (kg)
4.56
Tubuslänge (mm)
420–500
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William Optics Gran Turismo GT81 WIFD OTA — 81 mm triplet apochromat This refractor provides a 478 mm focal length at f/5.9. The manufacturer lists a 45 mm image circle and optional correctors for photographic use.
Manufacturer model: William Optics Gran Turismo GT81 WIFD OTA · Specifications checked against manufacturer data on 2026-11-03
