If you are shooting pictures with natural light, try for the best light you can. It is quite simple to find, and through a similar process, you can also find rainbows when the conditions are right.
Know where your brightest light source is (if shooting outdoorswith natural light, this will often be the sun.) Turn your back to it. Stick your hands out to either side, palms forward. Draw an imaginary line shooting out from your fingertips that stretches away to the far horizon. That humongous half circle in front of you will be your best light. Within that half circle you can try for several different lighting effects, keeping in mind the source of light.
Divide that half circle up onto four equal pieces- two on the right, and two on the left. The two sides are mirror images of each other (in regards to lighting), as long as the sun is directly at your back. The wedge closest to your hands on either side (B) is where you will have the most fun with shadows, where you can use them to help define shapes. This is the area that will work nicely with rolling hills, ripples in sand, casting a face half in shadow, creating curves on a body, etc. The middle two quarters (A) will be your more even light, with most of the surface being out of shadow, with rich tones.
What is wrong with the light in the other half of the circle, behind the palms of your hands? There isn’t necessarily anything wrong with it, it just won’t make your pictures stand out as well. The colors will be washed out, especially with landscapes that have any distance to them. Objects will also get more and more blocked up with shadows, the closer you rotate towards the sun. You will however have a chance to create silhouettes when you place your subject directly between you and your light source.
How do you put your back to the sun when it is directly overhead? You can’t. If you draw an imaginary line from the sun to your head, stretched your arms to the sides, and figured out where your light would be, it’s everything at your feet. Unfortunately everything is lit in such a way that either there are no shadows, because the sun is shining straight on it that you lose all depth and texture, or it becomes so blocked up with shadows and over exposure, that the pictures just won’t be very exciting. This is a large part of the reason why it is wise to use the morning and evening hours for photography. It’s not just warmer light, but better angles for lighting your subjects and using shadows.
Right about now, you are probably wondering what all of this has to do with the rainbows that the title propounded. Simple. If the conditions are right for rainbows (a mix of sun and rain), it is easy find the rainbow by putting your back to where the sun should be. If you draw an imaginary line from the sun, through your head, the rainbow will be in a circle 42 degrees out from that line. It can actually even be a complete circle if it is raining hard enough, and there are no shadows blocking the suns light. The way water diffracts light will always create the same angels from your place of perception relative to the source of light, placing the rainbow into that same relative space… Which just happens to be part of the area where you will find your best light for taking pictures. (If there is a double rainbow, it will appear at 51 degrees.)
It doesn’t matter if it is mist from a hose, rain from a cloud, spray from a waterfall, or dew drops in a spider’s web- it is always droplets of water catching and reflecting light, and water and light are very particular about how they interact. To find a rainbow, turn your back on the sun.
One fun thing about rainbows being an optical effect is that they always appear in the same place relative to you and the sun, so if you move… they move. You can drag them with you to improve the composition of your image (as long as you have enough time before it fades).