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ZWO IR-Cut Protective Window

ZWO IR-Cut Protective Window

by ZWO
SKU ZWO-D21IR-CUT1
CA$26.00 - CA$26.00
CA$26.00
CA$26.00 - CA$26.00
CA$26.00
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  • 21 mm or 25 mm diameter protective window for select ZWO cameras
  • Integrated UV/IR-Cut filter maintains natural color balance
  • 1/4 λ surface flatness preserves image sharpness
  • 1.1 mm thickness for correct optical path length
  • Seals sensor chamber from dust and humidity
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Downloads
  • Warranty

  • ZWO D21 IR-Cut Window

    The ZWO D21 and D25 IR-Cut Windows are precision-polished optical elements designed to protect your camera's sensor, offered in 21 mm and 25 mm diameters with a 1.1 mm thickness. The integrated UV/IR-Cut filter preserves true color balance, while the 1/4 λ surface flatness ensures that the window does not introduce any degradation to your final image sharpness.

    Precision Optics: 1/4 λ Flatness at 1.1 mm Thickness

    This is not simply a piece of glass; it is a critical optical component. The ZWO D21 window is ground and polished to a 1/4 λ surface flatness, a specification that guarantees it is optically transparent and will not distort the incoming wavefront from your telescope. This preserves the finest details on planetary surfaces and ensures tight, point-like stars. The 1.1 mm thickness is standard for ZWO cameras, ensuring no change in back focus when replacing a stock window.

    OEM Protection: 21 mm or 25 mm Diameter with UV/IR-Cut

    Designed as a direct factory replacement, the window seals the sensor chamber of compatible ZWO cameras from dust, pollen, and humidity. On the cameras it fits, the integrated UV/IR-Cut coating blocks the out-of-focus infrared and ultraviolet wavelengths that CMOS sensors are highly sensitive to. This prevents star bloat and delivers a clean, color-accurate image without requiring a separate filter.

    • Direct Fit: Replaces the original window on the ASI120MC-S and ASI178MC (D21) or the ASI174MM, ASI174MC and ASI174 Cool cameras (D25).
    • Essential Filtration: Acts as the built-in IR-cut filter on the cameras it fits, correcting for the sensor's infrared sensitivity to produce natural colors on targets like Jupiter's Great Red Spot and Mars' polar caps.
    • Sensor Safety: Provides a physical barrier that protects the delicate CMOS sensor and its microlenses from physical contact and environmental contaminants.

  • Which ZWO cameras are compatible with the D21 IR-Cut Window?

    The ZWO D21 IR-Cut Window is a direct replacement for the stock window on the ASI120MC-S and ASI178MC. The D25 IR-Cut Window fits the ASI174MM, ASI174MC, ASI174MM Cool and ASI174MC Cool.

    Why is 1/4 λ flatness important for the ZWO D21 window?

    A 1/4 λ (quarter-wave) flatness specification ensures the window is optically perfect and will not bend or distort light as it passes through to the sensor. A less flat window would act like a poor-quality lens, softening the image and reducing the fine detail your telescope resolves. This precision is critical for high-resolution planetary, lunar, and solar imaging.

    Is the ZWO D21 IR-Cut Window required for monochrome cameras?

    No. ZWO lists the D21 IR-Cut Window only for the color ASI120MC-S and ASI178MC. Monochrome cameras like the ASI290MM or ASI178MM use the D21 AR window, which protects the sensor from dust and humidity without blocking IR.

    If I see dust spots on my ASI178MC images, do I need to replace this window?

    Not necessarily. The first step is to try cleaning the exterior surface of the window with a sensor cleaning kit or rocket blower. If the dust motes remain fixed in the same position on your flat frames after cleaning, they are likely on the sensor itself, which may require removing the window for a deeper cleaning. You would only replace the window if it is scratched, cracked, or the coatings are degraded.

    Will using the ZWO D21 IR-Cut Window affect my focus when imaging the Moon with my ASI178MC?

    No, it will not affect your focus. The ZWO D21 is designed to be parfocal with the original window installed in the camera from the factory. At 1.1 mm thick, it maintains the correct optical path length, so you can replace a damaged window without needing to change your focuser position.

    How do I know if my ZWO camera's protective window is damaged?

    Damage can be physical or a degradation of the coatings. Look for obvious scratches or cracks. Coating failure can appear as blotchy or hazy patterns on the glass that cannot be cleaned off. These issues will show up in your images as fixed artifacts or a general loss of contrast that cannot be corrected with flat frames.

  • SKU ZWO-D21IR-CUT1
    Diameter 21 mm (D21), 25 mm (D25)
    Filter Type UV/IR-Cut Protective Window
    Thickness 1.1 mm
    Surface Flatness 1/4 λ
    Warranty 2 Years

    • D21 or D25 IR-Cut Window (per variant)

      × 1

  • ZWO 2-Year Limited Warranty