Below is a series of still frames that show the effect of focal length on an interview subject. Focal lengths of 35mm and shorter are considered "wide-angle" focal lengths while those of 85mm and longer are considered "telephoto". We filmed six shots of Nicole at six different focal lengths while maintaining the same aperture and ISO settings for each shot. For each different focal length, we changed the distance between Nicole and the camera so that she occupies the same rough area of the frame in each shot. The first two shots show the telephoto focal lengths of 135mm and 85mm:As you can see above, longer focal lengths tend to “flatten” images: the nose and fine lines on our subject’s face are less exaggerated, and the background appears closer to our subject (a phenomenon known as “background compression”). And because the background appears to be closer, longer focal lengths reveal less of the background area behind our subject, resulting in a more “intimate” or “cozy” aesthetic. The fact that longer focal lengths also reduce depth-of-field, making it easier to throw the background behind our subject out-of-focus, contributes to this aesthetic. The next shot shows a 50mm, or "normal" focal length. Our eyes are similar to 50mm fixed focal length prime lenses, so this is a very "natural" look. Notice that the background in this shot below appears to be a bit further away from our subject and a bit more in focus than in the telephoto examples above.
The next three shots use 35mm, 24mm, and 12mm focal lengths respectively. These focal lengths tend to exaggerate depth in images: facial features such as the nose and fine lines become enlongated, while the background appears to be farther away from our subject. This enlarged apparent distance from the background to the subject reveals more background area behind the subject, resulting in a “broader” and more “open” feel to the scene. Shorter focal lengths also increase depth-of-field, allowing more of the scene to stay in focus and enhancing the more “open” and “broader” aesthetic. However, focal lengths shorter than 28mm begin to produce deformations in the image such as barrel distortion, which causes horizontal lines to appear curved, and keystoning, which causes vertical lines to tilt inward towards the center of the frame. Such deformations are not flattering on a human interview subject, and should be avoided.
As mentioned above, the 24mm and 12mm focal lengths are not the best choices for filming interviews. When you compare the 12mm focal length image to the 135mm focal at the top of this post, you can *really* see the effect of focal length on an interview subject!
Joshua