It's all about distance

A good photograph is knowing where to stand -- Ansel Adams

Just about everything in photography is a balancing act. Shutter speed vs aperture, ISO vs noise, hard vs soft light, and on and on. One thing I don't see mentioned often is camera to subject distance. The balance here is the perspective--the relationship between the elements in the scene. The closer the camera is to the subject the smaller the background appears in relation to the subject. That's it. That's basically what you need to know.

I see a lot of people confuse this with lens focal length. You know--the old "telephoto lenses compress the scene" line. It is not the lens that is compressing the scene. All lenses have the same perspective when used at the same camera to subject distance. What happens is that we usually use longer lenses from greater distances between the camera and subject. Now go back and re-read  the last three sentences of the previous paragraph (they are in italic).

What the focal length does is determine the magnification of the subject and, along with the sensor size, the field of view. It doesn't alter the perspective. Let's look at the following animation. It has five frames that were all taken with the same camera and lens. The camera has a full frame 35mm sensor and the lens is a 35mm prime lens, all taken at the same aperture (f/2.8). For each subsequent frame in the illustration I took a step back (greater camera to subject distance) and then cropped the mannequin head to the same size in post-processing. I started at about 12 inches and finished at about 10 feet between camera and subject. The subject and background remained stationary, with the mannequin being 15 inches in front of the backdrop.

perspective.gif

Notice that as the camera is moved back away from the subject a few things happen. One, the look of the face changes radically in the first couple of frames. When in close the nose is much closer to the camera than the eyes and the ears, making the nose seem larger in comparison and also making the full face look narrower than it really is. this is caused by the camera being in close. The same relationship will be there with longer lenses, but their limited angle of view, greater magnification, and further closest focusing distance may not allow you to get the photo. You have to trust this condition being caused by distance and not focal length.

In the subsequent frames you see the look of the face compressing. As the camera moves back the relative sizes of the nose, eyes, and ears become closer and the image "compresses" even though I am still using the same wide-angle 35mm lens. Also notice that the background pattern gets larger as the camera is backed up. Go back to the italicized lines in the first paragraph again.

Just for comparison, here are a few more images. In the first set both images were taken at the same camera to subject distance using the 35mm lens and a 200mm lens. Notice that the perspective is the same. What changes between these images is the crop (the 35mm shot is cropped greatly, sacrificing resolution, the 200mm shot is the full frame) and Depth of Field (much larger in the image made with the 35mm lens, but that is another balancing act for another post).

200mm-vs-35mm.jpg

In this next pair of images both were taken with the 35mm lens, but at two different distances. In close you see the perspective "expansion" that comes from being in close. In the more distant image you see the perspective "compression" that is usually attributed to long lenses, but just comes from the distance. There is also an inset image to show the full frame that the image was cropped from. From the crop you can see that this isn't practical for most situations, but is here to show the point that the determining factor in the perspective of the image is distance, not focal length.

35mm-comparison.jpg

Bottom line is that you compress the scene by moving back, away from your subject. Then you use a long focal length lens to make the subject larger in the frame so you don't have to crop in and lose quality and resolution.

Thanks for following along! Hope this all made sense. Please follow up with any questions in the comments below.

John