Astronomy Specialist

FLUOROSTAR 91 F/5.9 APO TRIPLET

$2,054.00 USD
SKU: WO-T-FLT-91GD-RP33

William Optics

Apochromatic triplet

91 mm

f/5.9

540 mm

5.58 kg


Color: Gold
Style

 

The new William Optics Fluorostar FLT 91 is a three element air-spaced apochromatic refractor with a focal ratio of f/5.9 and a focal length of 540mm. Utilizing FPL-53 synthetic fluorite glass with STM coatings, this telescope provides excellent aberration correction and amazing optical performance.

The 3.3" dual speed rack & pinion focuser is smooth, stable and reliable, providing no slippage over long imaging sessions. The super smooth field rotator includes markings for every degree, and a solid thumbscrew position lock.

The CNC-machined and anodized handle bar with finder-style saddle is perfect for attaching a guide scope or other accessories. The FLT 91 also includes William Optics' innovative clear Bahtinov mask integrated into the lens cap. The Rotolock 2 inch adapter provides for a solid and efficient connection for a William Optics 2 inch diagonal, and other accessories.

William Optics uses high quality steel lens cells for their Gran Turismo and FLT triplet refractors. This is perfect for temperature compensation and will prevent pinched optics in cold weather conditions.

For best imaging results, it is recommended to pair the FLT 91 with its matching Flat6AIII 0.8x field flattener/reducer (with M92 adapter ring) or Flat68AIII 1.0x flattener.

Note: As the Flat6AIII / Flat68AIII an adjustable flattener, you must adjust the distance for your specific telescope. See the Instructions tab above.


FLUOROSTAR 91 F/5.9 APO TRIPLET spot diagram FLUOROSTAR 91 F/5.9 APO TRIPLET & Flat68III spot diagram FLUOROSTAR 91 F/5.9 APO TRIPLET & Flat6AIII spot diagram FLUOROSTAR 91 F/5.9 APO TRIPLET Zygo test report

 

Optical design

Air-spaced apochromatic triplet

Objective diameter

91 mm

Focal length

540 mm

Focal ratio

f/5.9

Image circle

46 mm with Flat68III, 44.4 mm with Flat6AIII

Compatible flattener

William Optics Flat6AIII

Mount attachment

290 mm Vixen-style dovetail bar

Focuser

Rack & pinion dual speed 3.3" diameter

Camera connection

M92 x 1, 2" Rotolock

Backfocus

TBA

Tube weight

4.165 kg (5.575 kg with accessories)

Tube length

441 mm (fully retracted), 510 mm (fully extended)

Tube diameter

TBA

Dew shield diameter

TBA

SKU

WO-T-FLT-91GD-RP33 (Gold), WO-T-FLT-91RD-RP33 (Red)

 

 

  • Fluorostar 91
  • Lens cap with Bahtinov mask
  • Finder saddle handle bar
  • 290 mm Vixen-style dovetail bar
  • Visual extension tube
  • Soft carry case

 

Note: Once you have unscrewed the rear adapter to the appropriate value in the table below, the remaining backfocus distance to make up will be 55mm from the rear M48 thread.  

Distance adjustment needed for correct backfocus with Flat6AIII 0.8x reducer

FLT91 5.4 mm
FLT120 10.7 mm

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FLUOROSTAR 91 F/5.9 APO TRIPLET.

FLUOROSTAR 91 F/5.9 APO TRIPLET

From $2,054.00 USD

Color

Style

  • OTA Only
  • With 0.8x Reducer

Optical design

Apochromatic triplet

Image circle

Focal ratio

f/5.9

Aperture

91 mm

Focal length

540 mm

Optical thickness

Threads

Cooled

Colour or Mono

Pixel size

Sensor dimensions

Resolution

Sensor diagonal

Quantum efficiency

Read noise

Fullwell capacity

Bit depth

FPS

Camera backfocus

Filter size

Filter size

Bandpass (FWHM)

Bandpass (FWHM)

Glass thickness

Mount type

Payload capacity

Latitude range

Dovetail saddle

Slew speed

Encoders

Periodic error correction

Counterweight shaft

Azimuth adjustment range

Internal diameter

Illuminated diameter

Compatible telescope external diameter

Weight

5.58 kg

Length

Width

Height

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