Rainbows are created by light bending through particles of water. They are usually seen most clearly with the sun behind you and the rainbow in front of you. Photographing them is straightforward – what makes an image with a rainbow stand out are the surroundings and the composition of the photo. Consider the rule of thirds and S-line within the shot; to learn more about these, read the tutorial.
Rainbow, You Connect member Monica Paterlini, Canon Digital IXUS 90 IS
Experiment with different focal lengths on your lens. A wide angle shot will capture a record of the entire rainbow but zooming into a detail may well create a more striking image.
Landscape photos often have a wide brightness range within their subject. The sky is many times brighter than the ground. This means that if the ground is well-exposed, there is a good chance that the sky will be over-exposed. This is why many landscape pictures have skies which are white, even though you remember them as containing striking cloud formations.
For correct exposure you should point your camera at the sky and lock the exposure using Auto Exposure Lock (AEL). Now recompose your photo. As long as * or AEL on your LCD screen remains visible, the original meter reading will be used, exposing for the sky.
Refer to your camera manual to discover how to set AEL on your camera.