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Fig. 7


Continuum Stokes I, Q, U, and V images (from top to bottom) of the sunspot observed with the SST in the 6302.5 Å Fe i line on 27 October 2009. The images on the left were calibrated with the described calibration scheme and the iterative method, the images in the middle used the direct method instead, and the images on the right were calibrated by straightforwardly applying standard calibrations as listed in Sect. 3 and using the direct method. The full range of the polarized images is −1.5% to  + 1.5%. The arrows indicate where sharp artifacts occur for some methods. Continuum offsets in the Q, U, and V images, most likely resulting from discrepancies in the telescope model, of up to  ~0.35% have been subtracted. The small dark region visible in the Stokes V image is actual signal in a region with strong downflows (see text).

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