There are a number of lenses that allow you to break the rules of depth of field. Because you can shift and tilt these lenses on an unusual axis not parallel to the image sensor, you can correspondingly tilt (up and down) and shift (side to side) the planes of focus in the photo. This technique is often used by large format, view camera photographers to attain unusually deep depth of field, where the shifts and tilts can be coordinated between both the front (lens stage) and back of the camera itself. Because the back of a DSLR is rigid there is less freedom of movement, and while specialty lenses can be used to create very deep depth of field, I use them for creating an almost angular plane of focus, thus a very shallow depth of field and “odd” focusing effects. What is most unusual is that these lenses allow you to turn the rules of depth of field on their head, if you will, by allowing you to have sharpness in, for example, one subject six feet away on the right side of the frame while another subject six feet away on the left side is quite unsharp.
While you can attain this effect via software, shooting with lenses that mount on your camera in the field is a much more visceral and engaging activity. I have used two types of lenses for this work-- “Lensbabys”, with various options for effects and operation, and a PC (perspective control) lens. Both are available for most every make of DSLR. They require manual focusing but usually can be used with automatic exposure, albeit with some occasional exposure compensation required.
PC lenses have a tilt and shift mechanism with various knobs and locks on the barrel. This allows you to tilt the lens to and fro and shift plus and minus. If you look at the back of the lens you will notice the rear element is recessed into the barrel. This so-called retrofocus-type construction allows the lens to be swung to and fro because the coverage of the lens circle exceeds the diameter of the sensor or film. Most of these pricey lenses are constructed so the tilts and shifts do not cause excessive vignetting, although you should watch for that with some more extreme movements.
You can play with the planes of focus in odd ways with one of the Lensbabys (www.lensbaby.com). This replaces the normal lens directly on your camera and allows you to shift the focusing planes so they are not parallel to the camera, something that is at odds with how we think about photographic sharpness. You do this by literally twisting or pressing down on one side of the lens; the bellows in the mount give way to make the lens surfaces sit at odd angles to the sensor. The lens can be shot wide open (usually about f/2.8) as supplied, or you can insert small diaphragms that create various aperture settings. I usually don’t use those stops as I want as shallow a plane of focus as possible.
Tools: PC (perspective control) lens or one of the Lensbaby models. Live View if available. Aperture priority or manual exposure mode. Manual focusing.
