The Sunrise Filter Imager (SuFI)
The SuFI instrument is part of the postfocus instrumentation package sitting piggy-back on the telescope. It provides high-resolution images of photospheric and chromospheric features at five wavelength bands in the visible and near ultraviolet at high cadence.
The optical arrangement is a Schwarzschild two-mirror system, magnifying the telescope secondary focus by a factor of five onto the detector, thus resulting in an effective focal length of 121 m. The sensor is a 2k × 2k UV enhanced fast read-out CCD. The field-of-view of the instrument is 15 × 40 arcsec2. Interference filters are employed to isolate the observed wavelength band. They have peak transmissions at wavelengths of 214 (10) nm and 300 (5) nm together with the Mg II k line (singly ionized magnesium) at 279.6 (0.48) nm and two filters for the Ca II H line (singly ionized calcium) at 396.8 (0.18 and 0.11, respectively) nm. The numbers in brackets are the filter widths.
In order to achieve near diffraction-limited imaging, a phase-diversity imaging technique is used by splitting the image in front of the CCD detector: half of the CCD area collects the focused image, while an optical delay line forms a second image with a defocus of approximately one wave on the other half of the CCD. Post-flight restoration of the images free from static aberrations of the optical path can thus be achieved.
SuFI was developed by the MPS.