From: Joe Smigiel (jsmigiel@kvcc.edu)
Date: 12/17/02-11:35:06 PM Z
Sam et.al.,
Sorry to nit-pick here, but the terminology is causing confusion. Perspective is solely determined by physical location in space, not by focal length. Your eye, a pinhole camera, a long lens, a telephoto lens, a normal lens, or a wide angle lens will all have the identically same perspective if located in the same spot. If you move in space, your perspective changes. It's that simple. Buying/using a long or short focal length lens will not change perspective regardless of what a camera salesman might tell you in a store.
If we consider two objects in space separated by some distance, they will show up on the film in the exact same *relationship* whether a long, normal, or short lens is used, as long as the photos are taken from the same physical point.
If you locate say, a 20mm lens on a 35mm camera at the same point as a 600mm lens on a 35mm camera (or 4x5 view camera or pinhole camera or whatever), the relationship between the two objects depicted on the film does not change as long as the angle of view includes them both on the film format and so long as you do not move your position in space. One can take the 20mm negative and enlarge it to identically match the two objects' image size on the negative shot with the 600mm lens. The objects will have the same relationship to each other. Now, the negative shot with the 20mm lens will produce a much grainier, less sharp print when the subjects' image sizes are matched on the print, but the perspective will be the same. That's where the psychological aspect comes into effect: a grainy print of those far-off cows or mountains is probably unacceptable and so the long lens and bigger camera is used to reduce the grain and add other operational headaches as you have pointed out (e.g., movement blur, reciprocity effects, etc.). It's all relative.
On the other hand, if you move the camera so the foreground object has an identical image size on the two films shot with different lens focal lengths, the relationship to the background object, and its image size, will change because you've changed your perspective by moving in physical space.
That's why the cardboard viewfinders mentioned earlier in the thread are so useful. They let one see and choose the exact point in space where the objects come into the proper relationship, and they inform which focal length will be needed from that point in space. If one doesn't have the correct focal length with them once their ideal picture and perspective has been identified by the card, then one *absolutely cannot* get that *ideal* picture. (So maybe one uses a shorter focal length lens and crops to exclude unwanted objects in the darkroom. Not the ideal, but it usually works...) This saves a lot of headaches in terms of setting up equipment in the field or developing useless negatives later on.
Position is the only determinant of perspective. Focal length only determines the magnification of an object on the negative.
joe
<<< stwang@direcTVinternet.com 12/17 11:09p >>>
Shannon,
(snip) the perspective is determined by the focal length.
Period.(snip)
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