William Optics Adjustable Flat6AIII Flattener/Reducer A 0.8× focal reducer and field flattener for the manufacturer's listed refractor combinations. Its optical system uses 3 elements in 3 groups.
Manufacturer model: William Optics Adjustable Flat6AIII Flattener/Reducer · Specifications checked against manufacturer data on 2026-11-03
A 0.8× focal reducer and field flattener for the manufacturer's listed refractor combinations. Its optical system uses 3 elements in 3 groups.
The telescope connection is M63x1; the camera connection is M48x0.75. Weight is 519.4 g. Optical length: 61.5 mm.
Backfocus varies by telescope: GT71: 64.1 mm; GT81: 62.1 mm; ZS81: 60.2 mm; ZS103: 57.5 mm; FLT91 with front adapter: 60.4 mm. Use the listed front or rear adapter where specified; backfocus and mechanical adjustment are different measurements.
William Optics manufacturer specification and compatibility chart
Spacing and mechanical fit require exact interfaces and reference surfaces. Named standards do not establish every system combination.
| Optical groups | 3 |
|---|---|
| Backfocus gt71 (mm) | 64.1 |
| Backfocus gt81 (mm) | 62.1 |
| Backfocus zs81 (mm) | 60.2 |
| Backfocus zs103 (mm) | 57.5 |
| Backfocus flt91 with front adapter (mm) | 60.4 |
| Camera thread engagement (mm) | 4 |
| Telescope thread engagement (mm) | 6 |
| Adjustment gt71 (mm) | 9.1 |
| Image circle gt71 (mm) | 44.4 |
| Adjustment gt81 (mm) | 7.1 |
| Image circle gt81 (mm) | 44.4 |
| Adjustment zs81 (mm) | 5.2 |
| Image circle zs81 (mm) | 44.3 |
| Adjustment zs103 (mm) | 2.5 |
| Image circle zs103 (mm) | 43.1 |
| Adjustment flt91 with front adapter (mm) | 5.4 |
| Image circle flt91 with front adapter (mm) | 44.4 |
| Spacing reference | Use the backfocus and adjustment setting for the named telescope and required adapter. Manufacturer model-specific values; not a universal camera spacing. |
| Filter connection | M48 filter thread behind the camera-side connection |
| Optical glass | Ohara glass, fully multi-coated triplet optics |
Ficha técnica
William Optics Adjustable Flat6AIII Flattener/Reducer A 0.8× focal reducer and field flattener for the manufacturer's listed refractor combinations. Its optical system uses 3 elements in 3 groups.
Manufacturer model: William Optics Adjustable Flat6AIII Flattener/Reducer · Specifications checked against manufacturer data on 2026-11-03
