Essentially, when a camera lense is attached to the body, the focal plane is straight ahead perpendicular to the camera. So if something is close, middle, and far away, and you focus on the middle item, the close and far away items will most likely be in some degree of out of focus.
Got that part?
Well, with free lensing (and tilt shift lenses) the focal plane shifts. Imagine taking a photo of a brick wall standing straight in front of it.. With a regular camera, the whole wall will be in focus, but with free lensing, either the left, right, top, bottom or middle can be in focus while the rest is out of focus.
If you want a more detailed and technical explaination (ie: more understandable) read here.
So I popped out my lens (literally) and decided to give it a shot on the only willing subjects available:
(told you that you'd see the rooster again)
As you can see in the before, the rooster is sharp, and the bear is slightly out of focus. Just as expected.
I also wanted to give it a good go outside and thought the "cool alley" might look interesting on a whole new focal plane.
I've also noticed that when I detach the lens, it throws the white balance off a bit, but I liked the reddish tones in the right photo so I left it.
I really think the detached image is much more interesting and artistic. A win, considering I saved around a grand not buying a tilt shift.
If you'd like to try this, you can read more at the link provided above, which will tell you what to do in each brand of camera. You can also see examples of other (and better) work in a free lensing flickr group.
If you try, share your links!