Wednesday, November 9, 2011

Perspective (again)

I've been seeing some tweets and Facebook messages about how lenses affect perspective and the drawing of the human face. My argument is that the lens doesn't cause the different look, but rather the distance from camera to subject does. The lens focal length just determines the angle of view or what fits into the frame. I could refer you to my previous blog post from this year on this. Or the one before that in 2009. Or even a post from 2007. But no, I'm going to write it all up again for your enjoyment.

I'm not saying that you should photograph everything with a short lens and then crop later to get your composition. But I am saying that you should determine your camera to subject distance to set your perspective and the relationship between items in the photograph and then select the lens focal length that fills the frame appropriately. Don't blame your lens(es) for perspective distortion (expansion or compression of the scene).

Here is a set of 3 images. I'm using a mannequin here instead of human so that there would be no movement between the photographs. One was taken with a 200mm lens, one with a 35mm lens, and one with a 16mm lens. The fourth image takes the 200mm and the 16mm images and combines them in separate layers in Photoshop. I then set the blending mode to "difference" to show how the two images compare. The pixel and noise structure of the two images accounts for the variations inside the facial area. But if you look at the outline of the face, you will see that it is exactly the same in both images. Changing the focal length did not change the perspective. Can you tell which image was taken with which focal length lens?

200mm and 16mm images overlayed
on each other in Photoshop's "Difference"
blending mode. The facial shape and
features are the same.

Here are the full frame originals to show the size differences due to the various lens focal lengths...
200mm lens from 8' away
35mm lens from 8' away
16mm lens from 8' away. Notice that
the relationship between objects
in the scene are the same even with
the widely varied focal lengths used

And to round out the comparison, here are three photos taken with the 200, 35, and 16mm lenses where the camera to subject distance was changed to try to maintain the approximate same size of the face in the frame.

200mm lens from 8' away. Facial features
are flattened. Nose, eyes, and ears are
all similar in size. The face appears slightly
wider than "normal"
35mm lens from about 2' away. Facial
features are more pronounced. The nose
is larger than the ears. The face is
narrower than "normal"
16mm lens from a few inches away.
Facial features are even more distorted.
The nose comes forward, the ears are
much smaller. The face is much narrower
than "normal"

Once again, I'm not suggesting that you take your portraits with a short lens from far away and then crop. I just want to show and help understand that camera to subject distance is what affects the perspective in a photograph. Too often the lens gets blamed for this. Select the appropriate lens for the situation.

Remember, a shorter lens doesn't cause the perspective change. But it does allow you to move in closer so that you get that distortion. And a long lens doesn't compress depth. Blow up the center section and you will find they match (like in the first three images above). Photographs taken with different focal length lenses, but from the same camera position, show exactly the same perspective in the section of the scene that is common to all the different angles of view of the various lenses.

Thanks for putting up with this again!

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