Stephen Johnson Tutorial: Perspective Correction
(excerpt from the book Stephen Johnson on Digital Photography unreleased revised electronic version)
As I was first learning to use a 4x5 view camera, one of the most amazing features was the rising front (lens) that allowed me to see a higher view by raising the lens relative to the film, without tilting the camera up. This ability to create precise geometric perspectives and keep vertical lines straight rather than converging was one of the fundamental interpretive tools I missed with my medium format and 35mm cameras.
Converging verticals are an interesting phenomena. We see them, they are real, but except where the convergence is extreme, such as at the base of a tall building, we tend to subtract them out of our visual take on a scene. Perhaps we don't notice them as much as our eyes create circular non-edged visions, without the straight lines of our photographic rectangles.
In the darkroom, we would occasionally tilt the paper easel and lens to correct for convergence and distortion, but the correction that could be done was very limited with a desire to maintain focus as well.
But now we have Photoshop. As much as I rail against overt intent to deceive or soup-up reality in images presented as photographs, I have generally seen perspective correction as one of the wonders of this new medium and creating the same effect I might seek with a view camera.
Of course there are now shift-tilt lenses available for 35 and medium format cameras, but they tend to be expensive and limited in their ability to do what I would have done with my view camera.
To correct for convergence, I tend to use the Transform/Distort command in Photoshop (with Grids turned on) which gives me individual controls of every corner. I work at pulling edges in rather than pulling them out, to straighten lines, throwing away data rather than making up more new intermediate pixels to render the now aligned lines.
This is an important capability, perhaps not quite as fundamental as minimizing chromatic aberration which is a natural consequence of trying to focus three different wavelengths of light on the same imaging plane. But I've always believed that it is a wonderful step forward where digital photographic techniques can eliminate common photographic problems that are not part of our normal human visual perception. Perspective correction rests somewhere in a middle ground between what we see, don't notice, but is then emphasized by the photographic process. I think we are well served by the ability to dial it back.
White River Light Station. Michigan. 2011.
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