The Sunrise Filter Imager (SuFI)

The optical arrangement of 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.

The SuFI filter wheel
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