The term “blue hour” refers to the unique coloring of the sky that occurs during twilight after sunset but before complete darkness. The sun has completely disappeared behind the horizon. The term “hour” is a bit confusing, because the period in our latitudes is usually only 15-20 minutes!
It is more or less dark for the eye, but due to the longer exposure times, the remaining light is collected and rewards the photos with a deep and rich blue (provided the sky is almost cloud-free). You can get more insight from https://gotoandlearn.com.
Take The Blue Hour Correctly
There are a few things to keep in mind to capture the blue hour on the photo, as there is little light at the right time.
A certain amount of preparation is, therefore, necessary. You should be at the desired location at the right time (calmly 30 minutes earlier) so that you can set up and align your camera/tripod in peace. Don’t forget to turn off any image stabilizer if you use the tripod !! Of course, a remote trigger is also helpful to avoid tangles when the camera is triggered. If you don’t have a remote release, you can also do it with the camera’s delayed self-timer. Then it goes to the camera settings.
Blue Hour Camera Settings
The autofocus will not work correctly in the dark. Therefore, switch it off on the camera (and possibly also on the lens). I then set the camera to “Infinite” (this is the sign that looks like a lying 8), or I don’t turn the focus ring as far as it will go, because it usually goes beyond “Infinity”, but stays with the marking Stand “Infinite”. Set the white balance to “Cloudy”. This corresponds to a value of 6000 Kelvin. If the white balance is set to “Automatic”, some cameras try to calculate the blue cast .. and that’s not what I want!
Of course, anyone who shoots in RAW (and I can only advise everyone) can later change the white balance on the computer without loss.
You can learn more from https://skylum.com/blog/photoshop-alternative-for-mac.