>Dave writes:
>> Changing focal length alone can definitely alter the relationship between
>> objects as seen in your view finder.
No. Karl is right. All changing focal length does is change the angle of view. The relationship between still objects (and space) in a scene (perspective) remains fixed as long as the photographer
does not move.
> This will be readily apparent if you
>> spend a moment with a zoom lens.
No. Exactly the opposite. The value of a zoom lies precisely in its
ability to change angle of view *without* altering perspective.
Think of it as cropping the scene when you rack the zoom, but
perspective remains unaltered. Do not take my word or Karl's
on this. Grab your zoom, put it on the tripod, and take 2 shots at either end of the focal range. Go home, develop and print both, cropping the wider one to show the same crop of the scene as
the longer one. Besides the artifacts of the larger blow-up, they
will be identical. As it would be if you shot the scene with a 12mm and
a 1200mm --- from the same place.
>Actually, appearance is precisely what I'm talking about. Follow me >thru... Place a small sign on a stake and stick it in the ground. Take >three paces and place another sign in the ground. Line yourself up >with the two signs and walk thirty paces. When you look back at the >signs the first one will look about 100 feet away and the second will >look about 10 feet farther away which is as it should look because >that is their relationship with each other and with you. Now with out >moving, take a shot thru your 35mm SLR 500mm lens at the signs. >They now look a lot closer to you and much closer to each other >which is also as it should look because the 500mm lens on a 35mm >SLR gives a ten X scope effect. The signs look about ten feet away >and one foot apart.
This is precisely wrong. Impossible as it seems, the relationship
remains unaltered.
>I do not understand your point. You say I can not alter spacial >relationships in an image by changing focal length and then claim to >prove it by changing length of focus (raising your enlarger head) and >altering spacial relationships in an image.
No. You cannot change the perspective in a negative via printing different size prints, or even changing enlarger lenses. By then
the deed is done. You can crop, though.
>Again, I don't understand your point. You can duplicate with your >enlarger what I can do with a zoom lens. So?
The point is, that for a given distance, perspective is fixed. All you
are doing is cropping the scene changing focal length.
Here is a simple way you can prove this to yourself now:
Construct a zoom viewer. Make a cut-out (1x1.5 rectangle) on
a card. Sit in one place, with a scene with several objects/components
at varying distances from you. No matter how close - or far -
you put the viewing rectangle (your focal length) to your eye,
the perspecive never changes until you move to another spot.
Try it.
--- Luis
