I agree with both of you. It's a matter of linguistic perspective ;-)
To add further words to the pot, I would say that perspective is
entirely a matter of the spatial relationship betweeen the viewer and
the objects viewed. I am speaking here in the geometric sense, not the
perceptual sense Andrew addresses.
In the geometric sense, Jeff and Walt are correct, a crop from a shot
taken with an 18mm lens and film with infinite resolution cannot be
distinguished from a shot from the same location taken with a 1000mm
lens. The same background areas are obscured in exactly the same way by
foreground objects. The relative sizes of the model's toes on the legs
sticking out in front of her and her eyes are the same. If I move
forward or back, both of these things change. If I move forward or back
to change these things and still want the same background area in my
picture or the size of the subject on film to remain the same, I must
change the focal length of my lens. Thus, if I am talking about a full
length shot of a couple of people, it is true that changing focal length
will change perspective, but that will be because I move toward or away
from the subjects to retain their size in the image.
Moose
Jan Steinman wrote:
From: "Jeff Keller" <jrk_om@xxxxxxxxxxx>
Focal length just changes the size of the image. There is no change in
the relative size and placement of objects (perspective)...
But that's the taker's point-of-view. I try to teach students to think in terms
of the subject.
Probably the difference in what you're saying is semantics rather than a
difference in understanding (which I'm pretty good at confusing).
I'd call it more a difference in attitude.
You are, of course, correct in saying that perspective doesn't change if the
camera-subject distance is unchanged. But (IMHO) that's a rather trivial use of focal
length, in most cases. (Yea, the "getting closer" part of focal length is handy
for shooting birds and large carnivores... :-)
I devote a whole unit in my class to having students get used to using focal
length to alter perspective. They already know how to stand in one place and
twist the zoom ring! :-)
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