"David Littlewood" wrote in message
...
In article , Nostrobino
writes

wrote in message
.. .
On 16 Jul 2004 02:16:09 GMT, ospam (PrincePete01)
wrote:
what i'm really trying to get is this....would a 50mm lens used on a
digital body (effective
75mm coverage) be an acceptable portrait lens?

peter

Actually, it will not make any deifference at all. Lens focal length
has nothing to do with perspective.

That depends on how you use the term "perspective." In the way that most
people use it, it definitely is related to focal length.

That's not the way most people use it.

You've never heard anyone speak of "wide-angle perspective" for example?


It means (in this context) the
apparent size of various parts of the scene relative to one another.
Objects further from the camera are reproduced at smaller magnification
than those closer to it, but the percentage change varies as the camera
is moved towards or away from the objects.

Yes. However, a wide-angle lens includes more objects and therefore has more
and different relationships, than a long lens.

Wide-angle lenses tend to exaggerate differences in distance, while
telephoto (or more correctly, long-focus lenses whether they are true
telephotos or not) produce the effect of spatial compression. These are
clearly differences in perspective, as it is perceived by the viewer.



Perspective is determined by position only. Focal length determines
field of view.

If that were true, wide-angle photos and long-lens photos would appear to
have the same perspective. They do not. I know you know this as well as I
do.



BTW, there is another apparently different use of "perspective" in
referring to the convergence of parallel lines which are at an angle to
the lens axis. However, on closer analysis, this is in fact exactly the
same phenomenon, i.e. the lines appear to get closer together as they
get further away from the photographer because the magnification is
lower.


In fact perspective wasn't even
invintet until railroads became popular. There is no such thing as a
telephoto/wide angle look. I just looks like there is a telephoto/
wideangle look

Perspective was well known to artists (well, some artists at any rate)
long before railways were built.

If it "just LOOKS" that way, then obviously there IS such a thing as a
wide
angle or telephoto look.

The only reason there is a "telephoto look" is because the pictures are
taken from a great distance.

Wide-angle photos taken from the same distance do not have a "telephoto
look," do they?

If I shoot buildings with an ultra-wide lens with the camera tilted upward,
the sides of those buildings will converge toward the top in a way that
appears very distorted, very spatially exaggerated. This is clearly a matter
of perspective, and meets every ordinary definition for perspective. If I
shoot the same buildings from the same position with a long lens, there will
be no such effect; on the contrary there will be a flattening and spatial
compression as verticals are made more parallel and distance differences are
made to appear less. This too is a perspective.




and if you really knew how to look, it wouldn't look
like there is a telephoto/wideangle to look at in the first place.

This is the fallacy of that whole argument. People look at photos as they
are, and any different appearance "if [they] really knew how to look" is
irrelevant.

The way this argument usually goes is something like this: If you take
two
photos of the same subject from the same position they have the same
perspective, whether you shoot with a wide angle, normal or telephoto
lens.

Anyone who actually does this will see VERY OBVIOUS differences in
perspective.

No they won't. They will simply see differences in the field of view,
and probably at different magnifications (and probably some differences
in grain or pixellation). Otherwise the two will be identical. The fact
that you think differently suggests that you can never have tried it.

Of course I've tried it. Try it yourself, in the example I've given just
above.



But the argument goes along these lines: Aha, but if you took
the central portion of the wide angle shot and enlarged it so that its
field
of view would be exactly the same as that of the normal or tele lens,
then
the perspective would also be exactly the same.

Yes, that's true, but people DON'T do that. The full shot taken with a
wide
angle lens has a wide-angle perspective, and the shot taken with a
telephoto
lens has a telephoto perspective. If you take a wide-angle shot and crop
out
everything except what would appear in a telephoto shot, all you've done
is
EMULATED the telephoto lens. The original PERSPECTIVE has been destroyed
by
what you removed.

No it hasn't. The field of view has been changed; the perspective
remains exactly the same.

Changing the field of view (from the same position) CHANGES the perspective,
is what I am saying.



This can be proven by always using a 7mm lens (any format) and adding
a twelve foot post to your enlarger. You do have to protect your
wideangle prints from nose gease because the proper viewing distance
is focal length times magnification.

But no one CARES about "proper viewing distance." If we see a shot taken
with a very long telephoto, we do not put it at the far end of a room
just
so we can look at it in the "proper perspective." That would, in fact,
defeat the whole purpose of using a long lens in the first place.

Similarly, no one puts his nose down on the print just because it was
shot
with an ultra-wide lens.

The only point of defining a print viewing distance is that it aims to
put you in the same relative position as that in which the photograph
was taken. I agree it's a pretty pointless exercise though, as mostly
one wants to have the perspective effect created by the original taking
position.

And focal length, yes.



This does mean the proper viewing
distance for an 8X10inch print from a full from a 35mm camera equiped
with a 500mm lens is eighty inches. Everyone know all this and in fact
is a given on at least one news list.

This sort of nonsense has been often repeated, that much is true. It's
still
nonsense, no matter how often it's repeated.

The reason the contrary view has "been often repeated" is that it is
true. Most of what you say is totally incorrect; I suggest you try
looking in some reputable textbooks.

I understand perfectly what you and your "reputable textbooks" are claiming.
I am saying that it's demonstrably wrong, which you can easily prove to
yourself.

Just remember that perspective is something that involves THE WHOLE PICTURE.
Once you accept that, your argument collapses.



If it were true and/or relevant, no one would ever bother using a 500mm
or
other long tele lens. What would be the point, if the print had to be
viewed
from some unnaturally and inconveniently long distance?

One uses a long lens to get a bigger magnification without having to use
excessive enlargement post-taking; this would result in very pronounced
grain or pixellation, and much lower resolution.

Those things aren't what matters as much as perspective. With 35mm for
example, why does anyone use a 105mm or so lens for portraiture? Because a
longish lens gives a more flattering perspective. You could use a 28mm lens
and move in to fill the frame just the same, couldn't you? But the results
would be horrid. Perspective is what makes the difference.

If you used the 28mm from the original 105mm position would the perspective
be the same (this is what you're claiming, right)? No, it would not. The 28
would produce not only a smaller image of the subject, but also more
convergence in parallel lines outside of the subject and, all in all, the
wide-angle perspective that you claim does not exist--but which anyone can,
in fact, see with their own eyes. How often do you have to see a certain
look with your own eyes before you admit that that look does, in fact,
exist?