Gran Turismo 81 back focus
- Aperture
- 81 mm
- Focal length
- 478 mm at f/5.9
- Image circle
- 45 mm
- Rear thread
- M63
- Corrector
- William Optics FLAT6AIII
Checked against the manufacturer’s documentation in September 2026.
Where to buy the William Optics Gran Turismo 81
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Cameras
| Camera | Back focus | Spacers | Result |
|---|---|---|---|
| Ares-C Pro | 62.1 mm | 28.1 mm | Exact |
| Artemis-C Pro | 62.1 mm | 44.6 mm | Exact |
| Neptune-C II | 62.1 mm | 33.1 mm | Exact |
| Poseidon-C Pro | 62.1 mm | 44.6 mm | Exact |
| Saturn-C SQR | 62.1 mm | 33.1 mm | Exact |
| Uranus-C | 62.1 mm | 33.1 mm | Exact |
| QHY183C | 62.1 mm | 28.1 mm | Exact |
| QHY183M | 62.1 mm | 28.1 mm | Exact |
| QHY268C (SBFL - Jan 2023 onward) | 62.1 mm | 26.6 mm | Exact |
| QHY268M (SBFL) | 62.1 mm | 26.6 mm | Exact |
| QHY294M Pro | 62.1 mm | 28.1 mm | Exact |
| QHY533C | 62.1 mm | 28.6 mm | Exact |
| QHY533M | 62.1 mm | 48.1 mm | Exact |
| QHY600M (SBFL) | 62.1 mm | 26.6 mm | Exact |
| ASI071MC Pro | 62.1 mm | 28.1 mm | Exact |
| ASI1600MM Pro | 62.1 mm | 39.1 mm | Exact |
| ASI183MC Pro | 62.1 mm | 39.1 mm | Exact |
| ASI183MM Pro | 62.1 mm | 39.1 mm | Exact |
| ASI2400MC Pro | 62.1 mm | 23.5 mm | Within tolerance |
| ASI2600MC Duo | 62.1 mm | 23.5 mm | Within tolerance |
| ASI2600MC Pro | 62.1 mm | 28.1 mm | Exact |
| ASI2600MM Duo | 62.1 mm | 23.5 mm | Within tolerance |
| ASI2600MM Pro | 62.1 mm | 28.1 mm | Exact |
| ASI294MC Pro | 62.1 mm | 39.1 mm | Exact |
| ASI294MM Pro | 62.1 mm | 39.1 mm | Exact |
| ASI533MC Pro | 62.1 mm | 39.1 mm | Exact |
| ASI533MM Pro | 62.1 mm | 39.1 mm | Exact |
| ASI585MC Pro | 62.1 mm | 39.1 mm | Exact |
| ASI585MM Pro | 62.1 mm | 39.1 mm | Exact |
| ASI6200MC Pro | 62.1 mm | 23.5 mm | Within tolerance |
| ASI6200MM Pro | 62.1 mm | 23.5 mm | Within tolerance |