(Editor’s note: Steve Inglima continues his thorough explanation of the view camera. The first post in this series introduces the view camera. This installment shows how tilting the lens results in more being in focus than is possible with only a small aperture set on the lens.)
The plain truth about focus in a single plane
By tilting either stage relative to the other, it is possible to redirect the principal plane of focus to intentionally deviate from what was parallel to the lens, or match another plane of interest. This allows the photographer to control that plane of focus, and make a decision about what plane of the image might best be most in focus. This is the control known as “Tilt.”
With the lens tilted, if the image plane, lens plane, and plane of focus intersect at a common line, then focus is at its greatest across that image plane. This is known as the Scheimpflug principle, named after Austrian army Captain Theodor Scheimpflug. This geometric “rule” was formulated to help correct perspective distortion in aerial photographs.
Using the tilt feature, we can change the principal plane of focus from being parallel to the plane of the subject (shown in the graphic above); to intentionally placing the focus plane along any area of the photograph we deem important to have in sharp focus. This can also allow us to use a wider range of f-stops than would have been necessary, as the only other option would have been to stop the iris down in order to achieve a sharp image. Keep in mind that if the only method that we employed to achieve focus would have been a smaller f-stop, and would’ve required the f-stop to be smaller than the diffraction limit (the minimum ƒ stop for maximum sharpness of that lens), sharpness could be compromised by that diffraction. If we can set the lens to the optimal f-stop for that lens resolution, and adjust the plane to focus for our depth-of-field control, we can achieve a sharper image at that redirected plane. I intend to cover the diffraction phenomenon in another episode 🙂
Tilting also allows us the aesthetic “trick” of intentionally putting objects out-of-focus which would have normally been in focus! It’s done by redirecting the plane of sharp focus to hyper blur parts of the image, creating a surreal appearance. It can render the scene as cartoon like, or as if the life sized scene were a miniature set.
The graphic below shows the top of the lens stage tilted towards the back of the piano. Note the dotted line “extensions” that show the subject, lens, and image planes intersection. When they meet at a common line, the focus is achieved over the entire image plane, and all of the keys of the piano are in focus (which makes Herr Scheimpflug very happy).
Making it work mandates that focus be checked on the ground glass with a magnifier in all areas where focus is of a concern quite rigorously. It’s best to establish this focus with the lens at maximum ƒ stop (wide open) as well as the target (working) aperture.
In the next installment Steve covers how the circle of coverage in a lens allows the shift feature of a view camera or the DSLR’s tilt / shift lens to work.