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William Optics Pleiades 181 Astrograph F/5.5 7-element with 3 ED glasses
William Optics Pleiades 181 Astrograph F/5.5 7-element with 3 ED glasses
William Optics Pleiades 181 Astrograph F/5.5 7-element with 3 ED glasses
William Optics Pleiades 181 Astrograph F/5.5 7-element with 3 ED glasses

William Optics Pleiades 181 Astrograph F/5.5 7-element with 3 ED glasses

by William Optics
SKU WO-T-P-181RD
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$19,998.00 USD
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$19,998.00 USD
$18,998.10 USD
$18,998.10 USD - $18,998.10 USD
$18,998.10 USD
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  • 181mm Aperture
  • 998mm Focal Length (f/5.5)
  • 7-Element Optical Design with 3 Super ED Glass Elements
  • 55mm Corrected Image Circle
  • 4.1-inch Rack & Pinion Focuser
  • No Flattener Required
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See exactly how your targets fit with the William Optics Pleiades 181 Astrograph F/5.5 7-element with 3 ED glasses, on real sky survey data.

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Check which filter and adapter sizes clear the sensor with the William Optics Pleiades 181 Astrograph F/5.5 7-element with 3 ED glasses, and how much light the corners lose.

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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • William Optics Pleiades 181 Astrograph F/5.5

    The William Optics Pleiades 181 Astrograph is a 181mm, 998mm, f/5.5 seven-element apochromat with three Super ED glass elements and a 55mm image circle, designed for imaging with medium format cameras. No flattener is required. It has a 4.1-inch rack-and-pinion focuser and weighs 18.7 kg with ring, dovetail and saddle.

    Optics: 7 Elements with 3 Super ED Elements

    It is a 7-element astrograph with Super ED glass x3: a seven-element, temperature-compensated lens system for minimal thermal distortion, with a Strehl ratio minimum of 0.96 across a greater than 55mm image circle.

    Its optional flattener entry reads "No Flattener Required": the correction is part of the telescope's own optics.

    181mm Aperture at f/5.5

    A 181mm objective has a Dawes limit of about 0.64 arcseconds and gathers about 2.7 times the light of a 111mm objective. At 998mm, a full-frame sensor covers about 2.1 x 1.4 degrees and a 44 x 33mm medium format sensor about 2.5 x 1.9 degrees.

    That scale suits galaxies, planetary nebulae and the brighter parts of nebula complexes, with large targets such as M31 needing a mosaic.

    A 55mm Image Circle for Medium Format

    The image circle is greater than 55mm, and supported formats are medium format, full frame, APS-C and M4/3. A 44 x 33mm medium format sensor has a 55mm diagonal; full frame (43.3mm) sits well inside.

    T-mount support covers Canon EF and RF, Nikon F and Z, Sony E, Pentax K, MFT (M4/3) and FUJI X.

    The 4.1-inch Rack-and-Pinion Focuser

    William Optics' spec list and price list give a 4.1-inch R&P focuser, compatible with EAF (an electronic automatic focuser), with 43 mm of travel. Its description prose says 3.7-inch; we follow the spec list.

    55mm Back Focus, Tilt Adjuster and Rotator

    William Optics' support guide for the Pleiades series gives a required back focus of 55mm, measured from the telescope's rear flat surface to the sensor. The telescope comes with three camera adapters, for 68mm, 54mm and 48mm threads, plus a tilt adjuster and a rotator.

    Cosmos Steering Wheel

    A Cosmos Steering Wheel allows handling, rotating and precise positioning of the telescope, for comfort during long sessions.

    Visual Use

    William Optics designed the Pleiades 181 for imaging and does not describe a visual configuration. Ask us before buying a diagonal or eyepieces for it.

    Mounting: Losmandy Dovetail

    The dovetail type is Losmandy, and the total weight figure includes ring, dovetail and saddle. It fits a Losmandy D style saddle.

    Weight, Length and Care

    The optical tube weighs 15 kg (33.07 lbs), and 18.7 kg (41.23 lbs) with ring, dovetail and saddle. Length is 1231mm retracted and 1496mm extended, and the dew shield is 230mm across. Add your camera and accessories and compare the total with your mount's rated payload.

    Let the telescope dry fully before storing it. Never aim the telescope or finder at the Sun without proper solar filters installed on the front of the telescope; doing so for even a moment may permanently damage your vision.

  • What mount does the William Optics Pleiades 181 need?

    The telescope weighs 18.7 kg with ring, dovetail and saddle. Add your camera and accessories and choose a mount with a Losmandy saddle whose rated payload covers the total with a good margin.

    Does the Pleiades 181 require a separate field flattener?

    No. It needs no flattener.

    How do I connect my camera to the Pleiades 181?

    Through one of the three supplied adapters, for 68mm, 54mm or 48mm threads, with the sensor 55mm from the telescope's rear flat surface.

    What does the 55mm image circle mean for a full-frame camera?

    A full-frame sensor (43.3mm diagonal) sits well inside the 55mm circle; at 998mm it covers about 2.1 x 1.4 degrees.

    Can the Pleiades 181 be used for visual astronomy?

    William Optics designed it for imaging and does not describe a visual configuration. Ask us first.

    How does the Pleiades 181 frame the Andromeda Galaxy (M31)?

    M31 spans about 3 degrees, more than the 2.1 x 1.4 degree full-frame field at 998mm, so it needs a mosaic. Its core region and companions M32 and M110 fit individually.

    What does William Optics say about the 7-element design?

    It describes a seven-element, temperature-compensated lens system with three Super ED elements, minimal thermal distortion and a Strehl ratio minimum of 0.96.

    Is the Pleiades 181 portable?

    It is relatively portable for its aperture, but at 18.7 kg with ring, dovetail and saddle and 1231mm long, it suits a heavy mount, typically in a fixed or semi-permanent setup.

    What is the tilt adjuster for?

    It corrects tilt between the camera sensor and the focal plane. William Optics includes it with the rotator and the three camera adapters.

    What focuser does the Pleiades 181 have?

    A 4.1-inch rack-and-pinion focuser with 43 mm of travel, compatible with EAF.

    How does 998mm frame the Horsehead Nebula (Barnard 33)?

    On full frame the field is about 2.1 x 1.4 degrees, which holds the Horsehead and the Flame Nebula (NGC 2024) together.

  • Lens Type 7-Element Astrograph
    Lens Elements 3x Super ED Glass
    Diameter 181 mm
    Focal Length 998 mm
    Focal Ratio f/5.5
    Image Circle 55 mm
    Focuser 4.1” Rack & Pinion Focuser
    Focuser Travel 43 mm
    EAF Compatible Yes
    Flattener Required No, integrated design
    Supported Camera Formats Medium Format, Full Frame, APS-C, M4/3
    T-Mount Support Canon EF, RF; Nikon F, Z; Sony E; Pentax K; MFT (M4/3); FUJI X
    Dovetail Losmandy Style
    Tube Length (Retracted/Extended) 1231 mm / 1496 mm
    OTA Weight 15 kg / 33.07 lbs
    Total Weight (w/ rings & dovetail) 18.7 kg / 41.23 lbs
    Required back focus (native, with built-in corrector) 55mm
    Rear / camera-side connection M68, M54 or M48 camera adapter
    Mount No

    • Pleiades 181 Optical Tube Assembly

      × 1

    • Tilt Adjuster

      × 1

    • Camera Angle Rotator

      × 1

    • M68 Camera Adapter

      × 1

    • M54 Camera Adapter

      × 1

    • M48 Camera Adapter

      × 1

  • William Optics 2-Year Warranty