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The reflection-bow (faint, located to the right of the primary arc) is caused by light reflecting up off the surface of the water. It was absolutely bucketing it down with rain and hail bouncing off the loch. HDR: 5 frames +/-0.7EV blended with enfuse. Olympus Pen-F, 7-14mm f/2.8 lens at 7mm.
Passing light: a vivid rainbow and less common reflection-bow (caused by light reflected up off the water surface), looking across Loch Rannoch toward Schiehallion.
Camera Make:OLYMPUS CORPORATION