3rd & 4th Order Rainbows

A recent OPOD featured Alec Jones (Bolton Halo Triangle) observation of a possible 3rd order rainbow. Here it is confirmed.. a 4th order.

Left:  Extra image processing by Nicolas Lefaudeux (opticsaround). He stacked the two images of Alec Jones and then used an RGB - grey subtraction technique.

The broad 3rd order bow circles the sun which is off image at bottom right. It is roughly the same size as the ordinary primary rainbow but is fainter and hidden deep in zero order glow and other scattered light.

Outside it is the reverse colour and even broader and fainter fourth order rainbow.

The 4th order bow was first imaged by Michael Theusner in 2011 just one month after Michael Gro�mann's first photograph ever of the elusive 3rd order.

All images ©Alec Jones, shown with permission
Image processing by Nicolas Lefaudeux:

Full details written by Nicolas here

Grey scale image
black adjustment
white adjustment
4x4 digital binning to reduce noise and increase dynamic range
background generation and subtraction
median to remove rain drops
stacking of the two images
reduction of highest spatial frequencies (~small radius blur)
final adjustments (curves, etc...)

Top image
RGB minus grey to remove residual intensity variations and enhance colour variations and combined it with grey scale image to get a good looking picture.
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