I remember when I received my first DSLR my senior year of high school from my Mom as a graduation present. Not satisfied with the stock 18-55mm zoom that came with it, I purchased a 70-200mm zoom so I could get close to the action and feel like an FBI agent on a stakeout. That’s what long focal lengths like 200mm are for, right?
Well, if you’re shooting wildlife or sports, where you can’t physically get closer but you need that tight crop, then yes. However, in most types of photography, you are not limited by sidelines. Why not get closer with your feet and shoot wider?
“But Tim, what’s the difference? If I can save time by just turning the zoom ring, that’s faster and easier!”
Here’s a little exercise to try out. Get a friend. Take your camera and use the widest angle you have available to you (zoom all the way out if using a point-and-shoot) and take a head/shoulders portrait of your friend. Now, use the longest focal length available to you (zoom all the way in if using a point-and-shoot) and take another head/shoulders portrait. You will be forced to move significantly further away for this one to crop correctly.
Now, switch repeatedly between the two photos. You should notice that on the first one, your friends face appears to be longer and their ears may even disappear behind their cheeks. The second photo will appear to be more how you are used to seeing them.
So what causes this? The technical term is perspective distortion. Your viewpoint creates distortions which are related to the ratios of how far away things are to your eye (or your camera). Things closer appear larger than things further away. Our brain compensates for this so if you put your eye in front of someone’s nose (preferably someone you know), you won’t notice this elongation nearly as much as a camera will portray it.
It’s often thought that the focal length is responsible for this effect. It is not. To prove it, take a picture of a your friends face while zoomed all the way out, but standing from the same spot you shot with your longest focal length. Switch between the photos. The ONLY two things that change is the way the photo is cropped and the depth of field (not related to this discussion). The perspective does not change at all. Your friend simply appears smaller.
So what do you do with this info? The method that I use the most is to first choose my camera position which affects perspective distortion and the amount of background I want to include, THEN I choose my focal length to crop the image how I would like it. Use this, and I believe you will find yourself with much more control over your image creation process.