Skip to content
Price match 30-day returns* Talk to an astronomer before you buy
William Optics 54mm Flattener Extender for GT81 WIFD

William Optics 54mm Flattener Extender for GT81 WIFD

by William Optics
SKU WO-AD-M80-54-M48
Save 5% Save 5%
CA$94.00
CA$94.00 - CA$94.00
CA$94.00
CA$89.00
CA$89.00 - CA$89.00
CA$89.00
Price Match Policy!
  • Provides a precise 54mm of optical length
  • Connects the FLAT68III flattener to M48 imaging trains
  • Designed specifically for the William Optics Gran Turismo 81 WIFD
  • Input Thread: M80 x 0.75
  • Output Thread: M48 x 0.75
Backordered
Request Stock Alert
Availability Info
Qualifies for FREE Shipping in Canada on orders over $500.
Vignetting Calculator

Will your imaging train vignette?

Check which filter and adapter sizes clear the sensor with the William Optics 54mm Flattener Extender for GT81 WIFD, and how much light the corners lose.

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

  • 54mm Flattener Extender for GT81 WIFD

    The William Optics 54mm Flattener Extender is a purpose-built adapter that provides exactly 54 mm of optical length for imagers using the GT81 WIFD telescope and FLAT68III flattener. This single component has an M80 x 0.75 thread for the flattener and an M48 x 0.75 thread for your camera or filter wheel, creating a rigid imaging train.

    The 54mm Spacer for FLAT68III on the GT81 WIFD

    Achieving a perfectly flat field with the Gran Turismo 81 WIFD and FLAT68III flattener requires precise back focus. This 54mm extender replaces the FLAT68III's original shorter adjusting adapter, as William Optics' GT81 WIFD manual describes. The camera sensor must then sit 55mm from the adapter, so your camera's own back focus plus any spacers must make up that distance. It replaces guesswork and spacer stacking with a single, correct-length solution.

    Secure M80 to M48 Threaded Connection

    This extender features an M80 x 0.75 thread that attaches to the FLAT68III and an M48 x 0.75 output thread, the common standard for 2-inch filters and full-frame imaging accessories. By using a single, machined piece instead of multiple generic spacers, you eliminate potential sources of flexure and tilt that can degrade corner star shapes.

  • Why do I need this specific 54mm Flattener Extender for my GT81 WIFD?

    This 54mm extender replaces the shorter adjusting adapter supplied on the William Optics FLAT68III when the flattener is used with the Gran Turismo 81 WIFD telescope. This ensures you achieve the specified 55mm back focus for a flat field and sharp stars corner-to-corner.

    How does the 54mm Flattener Extender help achieve the standard 55mm back focus?

    The extender does not supply the 55mm back focus itself. It replaces the original shorter adjusting adapter on the FLAT68III, and the 55mm back focus is then measured from the adapter to the sensor, made up of your camera's own back focus plus any spacers or filter wheel.

    What is the advantage of using this single 54mm Flattener Extender over stacking M48 spacers?

    A single, solid extender provides a much more rigid and stable connection. Stacking multiple smaller spacers can introduce flexure or tilt into the imaging train, which can lead to elongated stars in the corners of your images. This purpose-built extender guarantees alignment and stability.

    Will this 54mm Flattener Extender work with my full-frame camera and 2" filter wheel on the GT81 WIFD?

    Yes. The output thread is M48 x 0.75, which is the standard for connecting to most 2" filter wheels and full-frame camera adapters. You must ensure your total back focus, including the filter wheel and any other adapters, adds up to the required 55mm from the adapter to the sensor.

    Can I use this 54mm Flattener Extender with a different telescope, like a ZenithStar?

    No, this extender is specifically calculated for the focal length and optical design of the William Optics GT81 WIFD when paired with the FLAT68III flattener. Using it on another telescope will likely result in incorrect spacing and poor image quality, as different telescopes require different back focus distances.

    What are the thread sizes for the 54mm Flattener Extender?

    The extender has two threads:

    • Light-In Side (attaches to flattener): M80 x 0.75 thread
    • Light-Out Side (attaches to camera): M48 x 0.75 thread
  • Optical Length 54 mm
    Input Thread (Flattener Side) M80 x 0.75
    Output Thread (Camera Side) M48 x 0.75
    Kind Longer adjusting adapter (replaces the FLAT68III's original adapter)
    Telescope-Side Connection M80x0.75
    Camera-Side Connection M48x0.75

    • 54mm Flattener Extender for GT81 WIFD

      × 1

  • William Optics 2-Year Warranty