Last weekend we biked along the Don River. For me it was another chance to explore focusing with a tilted lens.
Looking inside a view camera can be quite startling.
There is nothing there.
This is in stark contrast to the innards of modern cameras which are packed with various technologies used in the production of an image or are related to that process.
This emptiness quite clearly exposes how simple it can be: A lens; a gap; a piece of film.
It's easy to be mislead by the wood and brass construction that there is no technology at all. But there is; the various knobs, levers and slides provide capabilities not available on most cameras: swing, tilt and shift.
In the normal camera the film plane, lens plane and focus plane are all parallel.
Swing and tilt (of the lens) change the relationship among these planes. Tilting the lens forward, for example, tilts the plane of focus proportionately such that it slides under the camera and projects off into infinity.
As I explored the subject of tilt I came across Scheimpflug. Captain Theodor Scheimpflug was an Austrian Army and Naval officer, born in October 7, 1865 and died in August 22, 1911. In the early 1900's he used cameras suspended from balloons for aerial photography for the purpose of creating accurate maps. To resolve the various distortions that result from imperfect alignment he developed a number of principles, one of which bears his name.
In order for a view camera image to be sharp, the rules of optics state that the film plane, the lens plane and the plane of sharp focus must intersect along a common line in space. That line is the Scheimpflug line. [Merklinger, Focusing the View Camera].
The objective of my first experiment was to get a sense of how it works--the set up and the execution--by walking through the steps. The first step is to establish the things to be in focus. Or more precisely, what is the plane of focus? Standing in a field (picture below) I picked the distant trees and a spot just under the camera. With the plane picked I determined how far below my camera the plane passed (J). With J, I could then calculated the necessary tilt of the lens [a = arcsin (f/J), where f = the focal length of the lens in meters]. I estimated the plane ran 1 meter below the plane of the lens, which was just about ground level. The result was a tilt angle of 8.62 degrees. [Note: implicit in the equation above is some a relationship between the tilt angle and the angle of the plane of sharp focus which I do not yet understand.]
I levelled the camera and then tilted the lens the prescribed amount. Rather than calculate the depth of field I set the aperture to f/22 and the speed accordingly.
Inspection of the shot confirmed the angled plane of focus was present. Point #3 corresponded to my estimation of the far point of the plane and point #2 the near point. Both have focus. In contrast is point #1 (which is on the approximately the same vertical plane as point #2) that is completely out of focus.
I have more work to do to fully understand the maths, but given the results are there to be had, I'm encouraged to explore further along this path.
We loaded our bikes into the trunk and headed south. We parked at the Brickworks on Bayview, and then rode a few hundred meters north along Bayview to Pottery Road where we caught the Lower Don River Trail. We rode north Don Mills.
Monday we drove down to Tommy Thompson Park. We were there early, there were few people, lots of birds. The air was still. It wasn't too hot but there was some humidity.
I realised I hadn't shot digital for a while. The convenience of digital was a nice change. Yet I'm now a little more patient. A little more thoughtful about what I shoot.