Fluorostar 91
Fluorostar 91
Fluorostar 91
Fluorostar 91
Fluorostar 91
Fluorostar 91
Fluorostar 91

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William Optics

Fluorostar 91

Regular price
$ 1,998.00
Sale price
$ 1,998.00
Unit price

This item is out of stock but you can place an order now and we’ll ship when it becomes available.

New for 2021!

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.



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

The Saddle Bar Handle, offers a solid handle with a built in dovetail chamber for use with the WO Uniguide scopes, or other Vixen style guiding/finder scopes.

New Focuser Knob

A larger fit designed for better ergonomics.

Field Rotator

The super smooth field rotator includes markings for every degree, and a solid thumbscrew position lock.

Soft Carry Case

The 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?

Fluorostar 91


Vixen Saddle Plate


Visual Extension Tube


Soft Carry Case


Handle Bar


Built-in Bahtinov Mask Cap

Like Astrophotography?

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More Astrophotography items

Personal Upgrade Path

Buy risk-free: When it’s time to trade up you’ll get the most value for your used gear.