What ever happened to rear swings AND tilts on field view cameras?

[Tin Can]

and often un needed

[Doremus Scudder]

Wilmarco,

Distortion is when a viewer can tell that there's something off or not normal in a photograph. I don't consider perspective to be a distortion, since its normal and expected unless very extreme. Correcting for "perspective distortion" is actually a distortion of its own making. This is entirely subjective and a matter of opinion. In nature photography without lines or angles, we're free from worry about "perspective distortion" paradigms. What you see on the ground glass is what you get.

Just to go off on a tangent here, but hopefully one that will add to the discussion regarding "perspective" and "distortion."

Any mapping of a three-dimensional scene through a lens onto a flat two-dimensional surface introduces distortion following the rules of projection. We are most familiar with this with the good old Mercator projection of most world maps, where Greenland ends up looking much larger than Australia, even though it is significantly smaller. This is a result of the relative distances of the projected objects from the point of projection together with the relative distances of different parts of the projection surface from the point of projection (think nodal point of a lens for the photographic analogue); the farther the projected image is from the point of projection, the larger it will be rendered on the projection surface.

An image projected on film gets similarly "distorted." First of all, more distant objects are rendered smaller on the projection surface. That, however, is intuitive, since we perceive objects at a distance to be smaller than the same object when closer. Still, it is a form of distortion.

That gets coupled with projection distortion resulting from the edges of the flat projection surface being farther from the projection point than the center. Objects at the edges of your film get stretched a bit, growing proportionally larger the farther from the lens nodal point they are. This is most apparent with objects at the edges of images made with very short focal-length lenses; circles get stretched into ovate shapes, squares into trapezoids, etc. This happens to some extent with all lenses; it's just not very apparent with longer focal lengths.

Perspective, when speaking of art and image-making, traditionally has to do with how many vanishing points there are in an image and where they are located. We are all familiar with the image of railroad tracks receding into the distance to a vanishing point on the horizon. We know they are really parallel, though. This is an example of the distortion introduced by relative distances between the objects being projected.

There is also the distortion introduced by the relative position of the projection plane to the object(s) being projected upon it (farther from nodal pont = larger). By altering the orientation of the projection surface (film) to, say a planar subject, such as a building façade, the vertical parallel lines can be made to recede to a vanishing point at either the top or the bottom of the image, or, as many architectural photographers prefer, remain parallel in the image. This is accomplished by making sure the camera back (film plane) is parallel to that of the building façade by either setting up the camera that way in the first place or by tilting the back so that it ends up in that parallel position. The same thing happens with horizontal lines and swing.

Similarly, non-parallel lines can be rendered parallel on the film by positioning the film plane appropriately so that the distance distortion introduced by projection ends up magnifying the smaller portions of the scene the right amount, and vice-versa.

Notice two things here: First, the distortion introduced by the edges of the flat projection surface being farther from the lens nodal point than the center is not eliminated. It's there all the time. Second, tilting or swinging the lens around the nodal point will not affect the perspective rendering on the projection surface, since the only things at play there are 1) relative distance from the subject and 2) relative distance from the nodal point. It will, however, affect focus, which is a related, but separate issue.

My point being: If you're photographing with a camera and flat film, you've got distortion and, you have perspective control by how you position the camera back relative to the subject (this whether or not the camera has swings or tilts; it's just that with a view camera we have more framing options). All this talk about "no distortion" is bunk.

Best,

Doremus

[Tin Can]

Easy to SEE on any iPhone

[Mark Sawyer]

Picasso once asked a man what his wife looked like. The man showed Picasso a photograph of her, saying that was what she looked like.

Picasso asked if she was really that small and flat.

All photographs are distortions.