Sergei explains: In late afternoon there were black clouds that came from the east (usually cumulonimbus comes from the west). Cumulonimbus covered almost all the sky and although it was not raining there was a bright primary and good secondary rainbow.



I photographed the bows and in 10 minutes it started to rain but still with some sun. It seemed to me that I saw something in the other [sunward] part of the sky. I saw it for an instant and couldn't see again. So I took two photos with a polarizing filter set in different angles to (1) enhance the bows and (2) filter them out.







I found nothing at the time on my elderly laptop but I remembered the photos 6 months later (November).



On the good monitor I edited the color balance and curves in Photoshop and was surprised to see an arc. What is this? I showed my photo to Vladimir Galynsky (Minsk, Belarus, an experienced observer of ice-halos). He told me that it was similar to a tertiary rainbow and advised to send the photo to you.



I tried some RAW-converters and the best result showed on the DxO optics converter. I made one tiff file of one raw file. [This is Image B at left]. But the 3rd order bow is still barely visible.



I opened the RAW file in another converter, Lightroom. 15 tiff files were generated with a range of exposures. Vibrance and contrast was added to all of them. The 15 tiffs were then combined in PhotomatixPro and this image was then processed further in PhotoShop.



LAB mode was used with an unsharp mask applied separately to channels A and B. Then, I selectively diminished the image saturation. These actions were repeated several times. [Image C at left].



{To improve the 3/4th order bow visibility further] I then used Gaussian blur and emboss tools. The rainbow part of this latest image was combined with Images 3 and 2 using 20-30 pixel feathered selections. Layers were combined with hard light mode and luminosity modes. Finally noise was reduced [Image D].



