How The Length of The Lens Influences Depth Of Field

“There are always two people in every picture. The photographer and the viewer.”

~ Ansel Adams

 So what else did you notice about all the photos in the last blog?

Wait, wait, I know!

They were all dogs…no…hold it….They were all parrots…ahhhh…they were all purple?

Hint…go back and look at the images in the last blog.

Oh…that’s it! They were all tight shots of animal heads, so that the focus was literally on the animal in front of the lens and nothing else. The cropping was done in the camera.

Good. Now you have two new tools. You have chosen a narrow depth of field to blur out the background and in addition, you have cut out everything possible around the subject by choosing a tight crop.

There is another thing that will help your portrait images. Use a long lens. The magnification of the subject is always pleasing, and at any given aperture, the longer the lens, the less depth of field because everything is compressed.

Let’s look at these two photos of Jenny.

In this photo, taken with a 55mm lens, we can see that the depth of field was fairly narrow, because even though the background is recognizable as a farm scenic, we can’t clearly make out the details behind her because they are not in sharp focus.

Let’s change our lens to a 200mm, and try again.

Ok, it’s not an apples to apples comparison, because it was taken with a different background in different light, but it does illustrate the point. This time, we can see the zone of focus very clearly. (Look at the grass in from of Jenny, and behind her…there is a very distinct zone of focus where she is walking, and nothing else is in sharp focus.) I couldn’t have made this image with a 55mm lens because too much of the scene would have been rendered sharp in the final image even if I chose an aperture of f5.6 or f8.

In thinking about lenses and the differences between them, remember that the eyes are about the equivalent of a 50-55mm lens, so anything with a shorter focal length is a wide angle lens (28mm) and anything longer is a telephoto (200mm).

Lenses are measured in millimeters (mm). Think of it as angles. The smaller the number, the wider the angle of view, so more of the scene is recorded in detail at each aperture number.

The larger the number, the narrower the angle of view, so less of the scene is recorded in detail at each aperture number.

So I bet you can guess what the assignment is for this week!

Take out two different fixed focal length lenses, or your zoom, and practice using them until you have a good sense of what each focal length will do to the depth of field in your images. Be sure that is the only variable you are working with. Keep the shutter speed and the aperture constant as you explore this concept.

Good shooting,

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