Sunday, February 12, 2012

Focal length: How long is your focal?

Waaaay back in November I started sharing the lessons I've been learning about photography. I've been using several different books and doing different exercises.

In my first post we learned about selecting image size and quality in our camera settings.

Today, we're talking about focal length. Focal length is the distance from the optical center of the lens to the camera sensor. This distance is measured in millimeters, so that's what those lens lengths mean. You know, it's a 50mm lens or a 28-105mm zoom lens. So focal length literally refers to the length of the lens. A long lens has a higher number (focal length) than a short lens. The smaller the focal length, the wider the angle, so a lens with a focal length of 35 or less is considered a wide angle lens.

So what's the point of knowing that when I'm taking pictures? Using the wrong focal length can give me distorted pictures with curved lines that are supposed to be straight and big noses on small-nosed people.

Today's exercise is to take a picture of the same thing several different times. Start with the smallest focal length on your zoom lens. Stand where the object fills your viewfinder and take the picture. Change the focal length and move so that the object fills your viewfinder again. Do this from several spots. When you look at the pictures, notice the curvature of the lines. Look for any distortion.

I chose to use the kit lens that came with my camera, a Canon T3. The lens is a 18-55mm zoom lens. I started at 18mm.

Notice how much of the front of the car is taken up by the grill. This is the "big nose" effect. Do this to a person, and their nose looks enormous.

I backed up and changed the focal length to 24mm. The grill seems smaller, less rounded.

I moved back and changed the focal length to 34mm. The front end definitely looks less bulbous.


I moved back last time and used my longest focal length, 55mm.

The moral of the story is that we don't want to use a wide-angled lens (shorter focal length) while standing too close to an object or a person. To make this even clearer, I made my Hillbilly smile for a couple shots.

18mm
55mm
See what I mean?

In the future, as we're taking pictures, we need to be aware of which focal length will give us the picture we want. I definitely want my Hillbilly to look like the lower picture.

Other posts in this series:

Amateur Photography Blogging
Getting to Know Your Camera
Changing Lenses


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