Free lensing is a technique used with interchangeable lens cameras in both film-based and digital photography. The lens is detached from the camera and held in front of the lens mount by hand during exposure. This technique can create similar effects as a tilt shift lens, but without the cost. Tilt shit lenses simulate a shallow depth of field where as free lensing actually shrinks the plane of focus.
How to Freelens
To focus whilst free lensing set your focus to infinity and move the lens forward and back from the sensor. You will see in the view finder how the focus plane shifts. Position what you want in focus and create an exposure.
This tenique can be used with a wide range of lenses but the one lens most often mentioned is a 50mm 1.4, praised for it being easier than other lenses for its wider aperture.
Freelensing is prone to light leaks due to the fact that you are holding the lens away from the sensor when creating exposures, this can often be used for dramatic effect.
Examples of Freelensing