https://i.ytimg.com/vi/kkdk1VaBE0k/hqdefault.jpg
download:
https://www.dropbox.com/s/h3xadmw83f3pe6s/envmap_optimizer_node_nudelZ.blend?dl=0
images for comparison:
https://www.dropbox.com/s/e62a34oe2crzjxb/envmap_optimizer_images.zip?dl=0
trick
https://support.solidangle.com/display/AFMUG/Ai+Sky+Shader#AiSkyShader-ReducingNoiseUsingTheRaySwitchNode
source
Link to this post!