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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.
Daystar Flat Cap Diffuser for Solar Imaging

Daystar Flat Cap Diffuser for Solar Imaging

by Daystar Filters
SKU DAY-FC90
$85.00 - $99.00
$85.00
$85.00 - $99.00
$85.00
Price Match Policy!
  • Easily take flat frames for solar imaging
  • Calibrates out the effects of dust spots, vignetting, and filter uniformity
  • Available in multiple sizes
4 in stock
Qualifies for FREE Shipping in CONUS on orders over $350.
  • Description
  • Specifications
  • In the Box

  • Daystar Flat Cap

    The DayStar FlatCap is a precision Gaussian diffuser used to capture flat field reference images for solar imaging. It is temporarily installed over the front of the telescope and deliberately blurs the solar disk so that no solar surface detail remains. The resulting image contains only illumination gradients and optical defects from the imaging train, which can then be removed during software calibration.

    How It Works

    The FlatCap diffuses incoming sunlight into a controlled Gaussian intensity distribution. This strong diffusion suppresses solar structure while preserving dust shadows, vignetting, and uneven field illumination. These characteristics make it well suited for producing consistent and repeatable flat frames in solar imaging workflows.

    Flat Field Calibration with FlatCap
    Disclaimer

    Flat field calibration will not correct Newton’s Rings or interference fringes. These artifacts must be eliminated optically before flat field acquisition.

    Construction

    The FlatCap is manufactured in the USA and uses a spun aluminum mounting ring combined with a polymer diffuser. It produces a Gaussian intensity profile with a 4-degree FWHM divergence angle, requiring exposure times approximately 100 times longer than normal solar imaging. The diffuser supports a maximum field of view of 1 degree when backlit by the Sun and transmits wavelengths from 350 to 800 nm. It is rated for operation from -10 to 100 °C (14–212 °F).

    FlatCap installed on refractor

    Compatibility and Sizing

    FlatCap models are sold by inside diameter. Measure the outside diameter of the frontmost component of your telescope or ERF, then round up to the next larger size. Included felt pads can be installed if needed to ensure a secure and centered fit.

    Model Fits
    FC90 80–89mm tube OD or 63mm ERF
    FC100 90–99mm tube OD
    FC110 100–109mm tube OD or 80mm ERF
    FC120 110–119mm tube OD or 90mm ERF
    FC130 120–129mm tube OD or 100mm ERF
    FC140 130–139mm tube OD
    FC150 140–149mm tube OD
    FC160 150–159mm tube OD or 130mm ERF
    FC170 160–169mm tube OD
    FC180 170–179mm tube OD or 150mm ERF
    FC190 180–189mm tube OD
    FC210 190–209mm tube OD

    Example: A telescope with a 160mm front diameter should use the FC170.

    Important Safety Information

    The DayStar FlatCap is not a solar filter and must never be used as one. It must be the first component to encounter light and must only be used in combination with a safe solar filter or a dedicated solar telescope. Improper use can result in eye injury or equipment damage.

  • Construction Spun aluminum mounting ring with polymer diffuser
    Intensity distribution Gaussian
    Divergence angle 4 degrees FWHM
    Exposure time adjustment factor 100x longer
    Maximum field of view 1 degree with Sun backlight
    Wavelength transmission range 350–800 nm
    Operating temperature -10 to 100°C (14–212°F)
    • Flat Cap

      Flat Cap

      × 1

    • Felt pads

      Felt pads

      × 3