In June when conditions for observing halos aren’t fine because of low full moon elevation, I have had my best observation ever. On cirrostratus veil divided from cumulonimbus cloud firstly appeared 9° halo and later thick halo at 22-24 area. After stacking 20 pictures, it turned out to be 23° and 24° halo. Fragments of 20° halo were not recognizable until stacking photos. Halos were seen at the highest intensity for about half an hour.
Martin Popek