Daystar Filters Imaging FlatCap – fits 90–99 mm tube OD (SKU: FC100) is a diffuser designed for taking flat field reference images in solar astrophotography. The FlatCap is a Gaussian diffuser temporarily installed on the front of the telescope during flat frame acquisition. By strongly blurring the image of the Sun, the reference frame reveals only defects within the imaging train, such as dust spots, vignetting and filter non-uniformity.

The Gaussian diffuser produces a smooth illumination pattern, allowing accurate flat field calibration during image processing. The FlatCap is mounted over the front of the telescope or an ERF filter during flat frame capture.

Key features

• diffuser for solar flat field calibration frames
• aluminum mounting ring with polymer diffuser
• Gaussian light intensity distribution
• removes vignetting, dust spots and filter non-uniformity during image calibration
• mounts on the front of the telescope or ERF filter

Technical specifications

• construction: spun aluminum mounting ring with polymer diffuser
• intensity distribution: Gaussian
• divergence angle: 4° FWHM
• wavelength transmission range: 350–800 nm
• maximum field of view: 1° with Sun backlight
• exposure time adjustment factor: approximately 100× longer
• operating temperature: −10°C to 100°C
• compatibility: telescope tubes with 90–99 mm outer diameter

Important notice

• FlatCap is NOT a solar filter
• do not use without a proper solar filter or solar telescope
• must be the first component in the optical path when taking flat frames