THE SWING-BACK Is used to prevent distortion when tilting the camera to take in a tall building; also to bring a distant and near object into focus at same time.
We focus on a distant object and find the foreground out of focus, because the focus is shorter for distant views than for near objects. For distant objects, we draw the lens nearer the ground-glass to get the focus; for near objects the lens needs to be further from the glass. To bring both in focus, we focus on a point in the center of the ground-glass; about half way be tween foreground and the distant object. In one case the focus falls a little behind the ground-glass, in the latter, it falls in front. So we use the swing-back, which we suppose to swing on its center, drawing back a little the upper part (the foreground), which pushes forward the lower part (distance), and this will bring both in focus, and at the same time it does not disturb the middle distance, as that falls in the center of the ground glass, which practically remains in about the same place.
So with the side-swing. In taking a picture with some object, a tree for instance, near us on the right, to bring it into focus we swing back the left side of the ground-glass, on which the tree shows, till it comes in focus, swinging it back just enough to bring that side in focus without disarranging the focus of the more distant view. When making use of the side-swing or swing-back, we can employ a larger stop than usual, and still preserve the depth of focus to obtain which a small stop is ordi narily used. A picture is said to have depth of focus, when the foreground and distance are both in focus, details showing plainly in both. From the artist's stand-point, details everywhere are not admissible.