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 M54 Extension - 21mm

ZWO M54 Extension - 21mm

by ZWO
SKU ZWO-M54-M54-21
$18.00 - $18.00
$18.00
$18.00 - $18.00
$18.00
Price Match Policy!
  • Adds precisely 21mm of optical path length
  • M54x0.75 male and female threads for secure connections
  • Prevents vignetting with full-frame sensors
  • Machined from black anodized aluminum to reduce reflections
Backordered
Request Stock Alert
Availability Info
Qualifies for FREE Shipping in CONUS on orders over $350.
  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • ZWO M54 Extension - 21mm

    The ZWO M54 Extension Tube adds exactly 21mm of optical path length, providing a critical spacing solution for achieving perfect 55mm back focus with full-frame cameras. Machined from a single piece of black anodized aluminum, this 21mm extender ensures a rigid, tilt-free connection in your M54 imaging train, preventing flexure that can compromise edge-of-field star shapes.

    Achieve 55mm Back Focus with Full-Frame Cameras

    Most field flatteners and coma correctors require a precise sensor distance of 55mm to deliver sharp stars across the frame. This 21mm extension is a key component in the ZWO ecosystem for reaching that standard. When combined with a ZWO full-frame camera (which typically has 17.5mm of back focus) and a ZWO 16.5mm extension, this 21mm piece completes the 55mm requirement without stacking multiple, less stable adapters.

    Secure M54 Threading for Large-Sensor Payloads

    The ZWO 21mm Extension uses M54x0.75 threads on both its male and female ends. This large-diameter connection provides a more rigid and stable optical train than the older M48 standard, which is critical when supporting the weight of a filter wheel and a heavy, cooled camera. The wider M54 aperture also prevents vignetting on large sensors, ensuring the corrected light cone from your optics reaches the entire sensor without being clipped at the edges.

    • Solid, Single-Piece Construction: Eliminates the potential for optical tilt that can occur when stacking multiple shorter, thinner adapters to achieve the same distance.
    • Internal Matte-Black Finish: The interior of the extension tube is anodized and baffled to absorb stray light, preventing internal reflections from reducing image contrast.
    • Seamless Integration: Designed to thread directly and securely onto other ZWO M54 components like filter wheels, off-axis guiders, and camera tilt adapters for a reliable, repeatable setup.

  • Why do I need the ZWO M54 21mm Extension?

    You need this 21mm extension to achieve the standard 55mm back focus required by most flatteners and correctors, especially when using a ZWO full-frame camera. It provides a precise, solid spacer that prevents optical tilt and ensures sharp stars across your entire image.

    How does this 21mm extension fit into a standard ZWO full-frame imaging train?

    A typical ZWO full-frame setup to achieve 55mm back focus consists of the camera's native 17.5mm back focus, a 16.5mm M54 extension, and this 21mm M54 extension. The total (17.5mm + 16.5mm + 21mm) equals 55mm, the ideal distance for most optical correctors.

    Will the ZWO M54 21mm extension cause vignetting with my full-frame camera?

    No. The M54 thread standard has a larger diameter than M48, specifically to accommodate the light cone required by full-frame (36mm x 24mm) sensors. This 21mm extension maintains that clear aperture, preventing the clipping of light that can cause vignetting.

    Is the ZWO M54 21mm extension made of plastic or metal?

    The ZWO M54 21mm Extension is precision CNC-machined from a single piece of aircraft-grade aluminum. It is then black anodized to increase durability and minimize internal reflections.

    Can I thread a 2-inch filter into this ZWO 21mm extension?

    This specific M54-to-M54 extension does not have filter threads. ZWO produces other adapters, often with an M54-to-M48 conversion, that are designed to accept 2-inch (M48x0.75) filters. This piece is designed purely for adding 21mm of spacing while maintaining a robust M54 connection.

  • Optical Length 21mm
    Male Thread M54x0.75
    Female Thread M54x0.75
    Material Aluminum
    Finish Black Anodized

    • ZWO 21mm M54 to M54 Extension Tube

      × 1

  • ZWO 2-Year Warranty