Daystar Filters Imaging FlatCap – fits 110–119 mm OD tubes or 90 mm ERF (SKU: FC120) is a Gaussian diffuser designed for capturing flat field calibration frames in solar imaging. The unit is temporarily installed over the front of the telescope when taking reference images. By strongly blurring the Sun, the resulting frame records only imperfections in the imaging train—such as dust spots, vignetting, or filter non-uniformity—which can then be removed during image calibration.

Key features

• diffuser for capturing flat field reference frames in solar imaging
• helps remove vignetting, dust spots and filter non-uniformity during calibration
• strongly blurs the solar disk to reveal only optical system defects
• Gaussian light distribution
• designed for temporary installation on the front of the telescope or ERF filter
• compatible with telescope tubes 110–119 mm OD or 90 mm ERF filters
• construction with spun aluminum mounting ring and polymer diffuser

Box contents

• DayStar FlatCap FC120 imaging diffuser

Technical specifications

• type: flat field imaging diffuser
• 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: approx. 100× longer
• operating temperature range: –10°C to 100°C
• compatibility: telescope tubes 110–119 mm OD or 90 mm ERF
• country of manufacture: USA

Warning: The DayStar FlatCap is not a solar filter. It must only be used together with a proper solar filter or solar telescope and must be the first component exposed to incoming light when taking flat field images.