Note

1. Most of the focal lengths except the ones of 35mm format in the table above are the ones that aren't generally used, since they are calculated out based on 35mm format.
2. Since the focal lengths in the table above are based on the view angle, some of them may be different compared with the ones in other tables.

The picture format is the area exposed through the lens when a picture is taken.
Now, it is standardized and grouped in several formats. In addition to this, the actual size of some formats differs a little from the formal size.
As the film format is larger, image quality gets higher. But on the other hand, the depth of field gets shallower and exposure needs more time due to insufficient of light.

The view angle shows the angle lined from principal ray of the lens to both ends of diagonal of the picture. Generally, there are two principal rays, one at front and the other at back. In this case, it means the one at back, the second principal ray. This is also the basis of the focal length (focal length is the length from the second principal ray to the film surface.), and so the view angle depends on the picture format and focal length.