William Optics FLAT6AIII special edition for Fluorostar 91
William Optics Adjustable Flat6AIII with M92 Thread Adapter – Tailored for the FLT91
This adjustable version of the Flat6AIII reducer/flattener is specifically equipped with an M92-to-M63 adapter, making it compatible with the rear threads of the new William Optics FLT91 telescope. While it’s the same high-performance unit as the standard P-FLAT6AIII, this version includes the M92 adapter to ensure a perfect fit with the FLT91. (Note: M48-threaded T-mount not included.)
Optimized for f/6–f/7.5 Refractors
The Flat6AIII is engineered to enhance the flat-field performance of refractors with focal ratios between f/6 and f/7.5, including the FLT91. It delivers exceptional illumination and field flatness, supporting up to 97% coverage of full-frame sensors for stunning, edge-to-edge image quality.
Telescope Compatibility and Adjustable Back Focus
Designed with flexibility in mind, the adjustable design of the Flat6AIII allows you to fine-tune back focus to accommodate a variety of refractors and camera setups. DSLR and mirrorless camera users can easily achieve optimal spacing for precise imaging results.
Technical Specifications 
Feature |
Details |
Sensor Compatibility |
Full-frame ready |
Optical Design |
Fully multi-coated triplet APO |
Glass Type |
High-grade Ohara optical elements |
Reduction Ratio |
0.8x |
Adjustable Spacing |
Ideal for fine-tuning back focus |
Filter Compatibility |
Supports 48 mm filters |
Construction |
Internally blackened and fully threaded to minimize reflections |
Finish |
Polished, hard-anodized aluminum with the signature William Optics look |
Camera Connection |
Accepts standard 48 mm T-rings |
Designed for Quality and Simplicity
Whether you’re capturing wide-field vistas or detailed deep-sky images, the Flat6AIII reducer/flattener ensures sharp, flat images across the field. Its user-friendly design and compatibility with a variety of refractors make it an essential upgrade for serious astrophotographers using William Optics telescopes