The William Optics Adjustable Field Flattener  improves the flat-field imaging performance of William Optics GT71, GT81, Z81, and Z103 refractors. 

Features of the William Optics Adjustable Field Flattener

• APO triplet optics made with Ohara glass. 
• Fully multi-coated to provide bright and flat field across 97% of full-frame sensors.
• Built with M63 threads on the telescope side.

The following telescope models can be used with the William Optics FLAT6AIII Adjustable Field Flattener

• Amount of Adjustment:
• GT71 - 9.1mm
• GT71 - 9.1mm
• GT81 - 7.1mm
• Z103 - 2.5mm
• Z81 - 5.2mm

• Back Focus:
• GT71 - 64.1mm
• GT71 - 9.1mm
• GT81 - 62.1mm
• Z103 - 57.5mm
• Z81 - 60.2mm

• Image Circle:
• GT71 - 44mm
• GT71 - 9.1mm
• GT81 - 44mm
• Z103 - 43mm
• Z81 - 44mm

• Refine your flat-field performance.
• Fully multi-coated Ohara glass optics.
• Reducing factor: 0.8X.