Have you ever noticed that most of the photos that people shoot are taken horizontally? Even when the subjects themselves are vertical--things like trees and other people and tall buildings, people try to squeeze them into a horizontal format. In fact, one of the biggest complaints I hear from photo editors at magazines is that even though virtually all magazines are essentially vertical, photographers still shoot more horizontal images.
I think the real reason that most of us shoot so many photos horizontally is because that's how cameras are designed to be held and used. The viewfinder is on the top in the middle, the camera controls are (mostly) on the top of the camera and the LCD on digital cameras is horizontal. But that doesn't mean it's the best orientation in creative terms. Lots of subjects cry out to be framed vertically and they'll seem a lot more balanced and powerful if you let them proudly express their height. So next time you spot a subject that's taller than it is wide, turn the camera 90-degrees and see if things don't look more natural.
By the way, those two saguaro cactus shown here were photographed in Sabino Canyon in Tucson, Arizona and they're two of the most photographed cactus in the state. They look like pals posing for the camera!
Male Northern Cardinal
5 days ago