Skip to content
IMPORTANT: Our store is located in Canada. All orders that include products manufactured outside of Canada or USA will be subject to tariffs and duties, regardless of the order value. US customers are responsible for all applicable duties and tariffs, and those will be billed by the carrier, except for the Lacerta upgrade kit, for which we collect them at checkout.
IMPORTANT: Our store is located in Canada. All orders that include products manufactured outside of Canada or USA will be subject to tariffs and duties, regardless of the order value. US customers are responsible for all applicable duties and tariffs, and those will be billed by the carrier, except for the Lacerta upgrade kit, for which we collect them at checkout.
ZWO M48 Extension - 16.5mm
ZWO M48 Extension - 16.5mm
ZWO M48 Extension - 16.5mm

ZWO M48 Extension - 16.5mm

by ZWO
SKU ZWO-M48-EXT16.5
$23.00 - $23.00
$23.00
$23.00 - $23.00
$23.00
Price Match Policy!
  • Adds exactly 16.5 mm of spacing to an M48 imaging train
  • M48x0.75 male and female threads
  • Wide 43.2 mm clear aperture prevents vignetting with full-frame sensors
  • Machined from black anodized aluminum for rigidity and stray light control
20 in stock
Qualifies for FREE Shipping in CONUS on orders over $350.
  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • ZWO M48 Male to M48 Female Extender - 16.5 mm

    The ZWO M48 Male to M48 Female Extender adds a precise 16.5 mm of length to your imaging train, solving a critical back focus requirement for many common astrophotography setups. This M48 threaded spacer is the component needed to achieve the standard 55 mm back focus distance with a ZWO cooled camera and its included 21 mm extender, in imaging trains that do not use an off-axis guider.

    Achieving the Standard 55 mm Back Focus

    Most field flatteners and reducers require a rigid 55 mm distance from their flange to the camera sensor for optimal edge-of-field star correction. ZWO cooled cameras typically have 17.5 mm of back focus, and the 21 mm extender included with the camera adds 21 mm. This leaves a 16.5 mm gap that this extender is machined to fill perfectly, eliminating the need to stack multiple adapters and the potential for optical tilt.

    M48 Threads for Unvignetted, Full-Frame Imaging

    This extender uses M48x0.75 threads on both the male and female sides, maintaining a wide, unvignetted light path from your corrector to your sensor. Unlike narrower T2 (M42) threads, the 43.2 mm clear aperture is essential for illuminating the corners of full-frame sensors without dimming or clipping the starfield. The single-piece, black anodized aluminum body ensures rigidity and absorbs stray light.

  • Why do I need this specific 16.5 mm ZWO M48 extension?

    This 16.5 mm length is required to achieve the standard 55 mm back focus when using specific ZWO components together. A typical ZWO cooled camera (17.5 mm) plus the included 21 mm extender plus this 16.5 mm spacer equals exactly 55 mm.

    Do I need the ZWO M48 16.5mm extension if I use an off-axis guider?

    No. The 16.5 mm extension is used in imaging trains without an off-axis guider (OAG). An OAG adds its own optical length, so it takes the place of this spacer. When you add an OAG or a filter wheel, calculate your spacing from the optical length of each component so the total from the corrector flange to the sensor is 55 mm.

    What are M48 threads and why are they important for this ZWO extension?

    M48 threads (also known as "wide T-threads" or 2-inch filter threads) have a diameter of 48 mm with a 0.75 mm pitch. They provide a larger clear aperture than older T2 (M42) threads, which is critical for preventing vignetting (darkened corners) on cameras with large sensors, such as full-frame or APS-C formats.

    Is the ZWO M48 16.5mm extension threaded for filters?

    No, this is a spacer extension, not a filter cell. It is not designed to have filters threaded directly into it. Filters should be placed in a dedicated filter wheel, filter drawer, or threaded onto the nosepiece of your camera or the front of your reducer.

    Is this ZWO 16.5mm spacer compatible with non-ZWO equipment?

    Yes. As long as your other components use standard M48x0.75 male and female threads, this extender will connect perfectly. It is a universal part for any imaging train that requires precisely 16.5 mm of M48 spacing.

    What is the total length added by this ZWO M48 extension?

    The extender provides exactly 16.5 mm of optical path length. The length of the male threads is not counted, as they seat inside the female connector of the next component in your train.

  • SKU ZWO-M48-EXT16.5
    Connector Type (Side A) M48x0.75 Male
    Connector Type (Side B) M48x0.75 Female
    Length 16.5 mm

    • ZWO 16.5 mm M48 Male to M48 Female Spacer Extension

      × 1

  • ZWO 2-Year Limited Warranty