The FLT 91 is the perfect Apochromatic refractor for visual and photographic astronomers demanding excellence in a midsize telescope. The three-element optical design features a 91mm aperture using FPL-53 glass. The STM-coatings and superb quality provide excellent optical performance and unmatched value.
RotoLock
The Rotolock 2 inch adapter provides for a solid and efficient connection for a WO 2 inch diagonal, and other accessories.
Bahtinov Mask (Patented)
The retractable dew shield features a removable lens cover, with our patented Bahtinov Mask revealed by unscrewing the face plate. The clear design allows for brighter star patterns, and precise focusing for astrophotography.
Versatile Saddle Bar Patented
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New Focuser KnobA larger fit designed for better ergonomics. |
Field RotatorThe super smooth field rotator includes markings for every degree, and a solid thumbscrew position lock. |
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Soft Carry CaseThe standard package comes with a soft carry case. |
Technical Specifications
Lens Type | Apochromatic Triplet Prime Lens |
Focal Length | 540mm |
Diameter | 91mm |
Aperture | f/5.9 |
Flattener | FLAT 6A III x0.8 / FLAT 68 III x1.0 |
Focuser | Dual Speed 3.3″ R&P Focuser |
Color | Red / Gold / Space grey |
Lens Material | FPL-53 |
Strehl Ratio | 0.95+ |
Camera Format | Full Frame DSLR / Mirrorless / CMOS / CCD |
Test Report | Zygo test report available at additional cost |
T-Mounts Supported | Canon EF, RF / Nikon F, Z / Sony E / Pentax K / Micro Four Thirds (M4/3) / Fuji X |
Retracted Length | 441mm |
Extended Length | 510mm |
Extension Tube Length | 40mm |
OTA Weight | 4.165Kg |
Total Weight | 5.575Kg |
Extension Tube Weight | 0.105Kg |
What’s in the Box?
![](https://williamoptics.com/media/products/fluorostar-91/flt91.jpg)
Fluorostar 91
![](https://williamoptics.com/media/products/fluorostar-91/saddle.jpg)
Vixen Saddle Plate
![](https://williamoptics.com/media/products/fluorostar-91/extension.jpg)
Visual Extension Tube
![](https://williamoptics.com/media/products/fluorostar-91/carry-case.jpg)
Soft Carry Case
![](https://williamoptics.com/media/products/fluorostar-91/handle-bar.jpg)
Handle Bar
![](https://williamoptics.com/media/products/fluorostar-91/bahtinov-mask-grey.jpg)