I saw this rainbow in the Eastern Sierras near Bishop, California. I shot it handheld with the Sony A1 and the 100-400mm GM lens at 100mm, f/4.5, ISO 100.

Post processing included increasing contrast and slightly boosting the saturation of the rainbow. Oddly, the sky to the right of the rainbow is much bluer than on the left. That is natural and was not affected by my post-processing.