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Recommended field flattener for William Optics GT71, GT81, Z81 and Z103.

M48 Camera Side Threads

Maximum Backfocus

GT71 = 64.1mm
GT81 = 62.1mm
Z81 = 60.2mm
Z103 = 57.5mm

Adjustment Setting for 55mm Backfocus

GT71 = 9.1mm
GT81 = 7.1mm
Z81 = 5.2mm
Z103 = 2.5mm