Source : https://snapshot.canon-asia.com
EOS 5D Mark IV/ EF24-105mm f/4L IS II USM/ FL: 35mm/ Aperture-priority AE (f/11, 1/320 sec, EV±0)/ ISO 800/ WB: Daylight
Photographing a rainbow is actually not difficult, as long as you know the tricks.
1. Time to shoot
Rainbows are usually found during the rainy season. Most rainbows appear in the morning in the western sky and the colors are better, while in the afternoon they usually appear in the eastern sky with softer colors and less contrast with the colors of the clouds and sky.
2. Composition
The composition when photographing a rainbow will usually be more interesting if it is seen from end to end. But usually it is more difficult to get because sometimes limited location can also have an effect. But you can overcome this by finding a spacious place and using a wide lens, 16mm or 17mm. If you use a smartphone, you can use panorama mode. You can also use the HDR (High Dynamic Range) feature to make your photos more contrasty.
EOS 5D Mark IV/ EF24-105mm f/4L IS II USM/ FL: 60mm/ Aperture-priority AE (f/11, 1/320 sec., EV±0)/ ISO 400/ WB: Daylight
3. Use PL filters
You can use a PL/polarizing filter to make the rainbow colors more attractive.