William Optics Fluorostar 91
William Optics
William Optics Fluorostar 91 is a 91 mm Triplet APO refractor for wide-to-mid-field nebulae and general deep-sky imaging.
Best Current Offer
Specifications
Optics
- Optical design
- Triplet APO refractor
- Aperture
- 91 mm
- Focal length
- 540 mm
- Focal ratio
- f/5.9
- Dawes limit
- 1.27"
- Glass / elements
- Triplet APO with FPL-53-class glass
Imaging
- Image circle
- 43 mm
- Camera format
- Full frame / APS-C / Micro 4/3
- Full-frame coverage
- Yes
- Back focus
- Depends on selected William Optics flattener/reducer
Mechanical
- Focuser
- Rack-and-pinion focuser
Specifications
- Weight
- 4.165 Kg
Astrophotography Fit
Best for wide-to-mid-field nebulae and general deep-sky imaging when the mount, camera format, and correction hardware are chosen as one system.
William Optics Fluorostar 91 sits in the telescope slot for wide-to-mid-field nebulae and general deep-sky imaging. The useful headline specs are aperture 91 mm, focal length 540 mm, f/5.9.
Camera coverage: Full frame / APS-C / Micro 4/3. Image circle: 43 mm. Back focus: Depends on selected William Optics flattener/reducer.
Refractors keep the field routine calmer: no regular collimation, predictable cooldown, and a clean path to autofocus and filtered imaging. The tradeoff is aperture and reach.
Best paired with
- Corrected field flattener or reducer when the design requires one
- Cooled APS-C or smaller astro cameras matched to the image circle
- Autofocus, guide scope or OAG, and a mount with comfortable payload margin
Not recommended for
- Large full-frame sensors unless the corrected field supports them
- Very small travel mounts near their realistic imaging payload limit
- Buyers expecting one telescope to be ideal for every target size
Where To Buy
Some links on this page are affiliate links. Prices and availability are pulled automatically from each retailer and updated daily.
| Retailer | Price | Availability | View Offer |
|---|---|---|---|
| Cloud Break Optics Cloud Break Optics | $2,198.00 | In stock Updated 8/4/2026 | View Offer - $2,198.00 |
| Mile High Astronomy Mile High Astronomy | $2,198.00 | In stock Updated 8/4/2026 | View Offer - $2,198.00 |
Price History
Chronological retailer pricing with out-of-stock points shown at reduced opacity.