The High Resolution Telescope of the Polarimetric and Helioseismic Imager on Solar Orbiter (SO/PHI-HRT) operates in an extreme observational environment, observing the Sun as close as 0. 28;au. The high thermal load and large illuminating field puts high demands on the instrument in terms of both imaging performance and false light control. Our aim is to characterise the amount of stray light (false light) within SO/PHI-HRT, apply a correction, and re-compare the data products with the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory (SDO/HMI). We analysed solar limb profiles and a Mercury transit to quantify the amount of stray light and added a correction term when partially reconstructing the SO/PHI-HRT images. For the comparison with SDO/HMI, we used data from the 2023 March Solar Orbiter inferior conjunction and compared the magnetic fields on a pixel-by-pixel basis. Increased continuum intensity contrast in the quiet Sun, and darker intensity levels, are found in strong magnetic features. Consequently, much stronger fields are inferred in these features. Comparing the stray light corrected data with that from the standard SDO/HMI data products results in a much closer agreement across all vector magnetic field components, particularly when the cadence and noise levels are identical. In most solar features, SO/PHI-HRT infers stronger fields than the SDO/HMI line-of-sight (LoS) magnetograms. Compared to the vector magnetic field from SDO/HMI, the two are very well aligned, with only slight differences in the strongest field regions (where |B|>1600;G or LOS |>1300;G).
Sinjan et al. (Mon,) studied this question.