William Optics Flat68III Field Flattener A 1.0× field flattener that preserves the telescope's native focal length for the manufacturer's listed refractor combinations. Its optical system uses 2 elements in 2 groups.
Manufacturer model: William Optics Flat68III Field Flattener · Specifications checked against manufacturer data on 2026-11-03
A 1.0× field flattener that preserves the telescope's native focal length for the manufacturer's listed refractor combinations. Its optical system uses 2 elements in 2 groups.
Mechanical interfaces
The telescope connection is M92x1; the camera connection is M48x0.75. Weight is 718.2 g. Optical length: 64.5 mm.
Spacing and telescope selection
Backfocus varies by telescope: GT81 with back adapter: 57 mm; GT102: 68.6 mm; GT153: 57.8 mm; ZS126: 58 mm; FLT91 with back adapter: 60 mm; FLT120: 65.7 mm; FLT132: 62.7 mm; FLT156: 57.6 mm. Use the listed front or rear adapter where specified; backfocus and mechanical adjustment are different measurements.
Use telescope-specific spacing; GT81 WIFD and FLT91 require the documented adapter. Optical body length is not backfocus.
Additional specifications
Optical groups
2
Backfocus gt81 with back adapter (mm)
57
Backfocus gt102 (mm)
68.6
Backfocus gt153 (mm)
57.8
Backfocus zs126 (mm)
58
Backfocus flt91 with back adapter (mm)
60
Backfocus flt120 (mm)
65.7
Backfocus flt132 (mm)
62.7
Backfocus flt156 (mm)
57.6
Camera thread engagement (mm)
4
Telescope thread engagement (mm)
6.5
Adjustment gt81 with back adapter (mm)
2
Image circle gt81 with back adapter (mm)
44.4
Adjustment gt102 (mm)
13.6
Image circle gt102 (mm)
44.4
Adjustment gt153 (mm)
2.8
Image circle gt153 (mm)
44.4
Adjustment zs126 (mm)
3
Image circle zs126 (mm)
43.4
Adjustment flt91 with back adapter (mm)
5
Image circle flt91 with back adapter (mm)
43.4
Adjustment flt120 (mm)
10.7
Image circle flt120 (mm)
44.4
Adjustment flt132 (mm)
7.7
Image circle flt132 (mm)
44.4
Adjustment flt156 (mm)
2.6
Image circle flt156 (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.
69466
Scheda tecnica
Formato camera
Full frame, APS-C and Micro Four Thirds
Filettatura camera
M48x0.75
Elementi ottici
2
Lunghezza ottica (mm)
64.5
Fattore di riduzione
1
Filettatura del telescopio
M92x1
Peso (g)
718.2
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William Optics Flat68III Field Flattener A 1.0× field flattener that preserves the telescope's native focal length for the manufacturer's listed refractor combinations. Its optical system uses 2 elements in 2 groups.
Manufacturer model: William Optics Flat68III Field Flattener · Specifications checked against manufacturer data on 2026-11-03
