perspective w/ 35mm lenses?

"David Dyer-Bennet" wrote in message
...
"Nostrobino" writes:

The first post I have here gives the reply, "Actually, it will not make
any
deifference at all. Lens focal length has nothing to do with
perspective. In
fact perspective wasn't even invintet until railroads became popular.
There
is no such thing as a telephoto/wide angle look. . . ."

This is what I originally disputed. OF COURSE there IS such a thing as a
telephoto look or a wide-angle look, that particular look in either case
IS
because of the characteristics of perspective, those characteristics ARE
related to the focal length of the lens used, and anyone whose eyes and
brain work together properly is able to see this.

Can you seriously tell me that if, for example, you walked around a city
with an SLR and two lenses, a 20mm and a 200mm, taking hundreds of
pictures
and interchanging the lenses frequently, taking no notes about distance
or
which lens was used for which shot, etc., then viewing the photos even
months or years later you would NOT be able to tell which shots were
taken
with the 20 and which with the 200?

There are clues other than the size relationships of objects in the
pictures to what lens they were taken with.

Of course, and those clues are called "perspective."


And it's sufficiently
unconventional to drastically crop a picture that you get some direct
indication of angle of view from the picture.

Have you ever seen one of those brochures or counter mats at a camera
store that give a series of pictures taken by all the lenses in some
company's lineup from the same position? If you look at those
pictures, you will see that each one could have been cropped out of
the center of the next-wider one and nobody could tell the
difference. That's a simple, direct visual proof of the canonical
position that camera-to-object distance is the only thing that affects
perspective.

Certainly not, because perspective is a function of the picture in its
entirety. When you crop out parts of the picture as you describe, you change
its perspective.



I don't think you are going to tell me that. Now tell me HOW you could
tell
the difference.

Guess you lose, eh?

No, you haven't answered the question.



What I am saying is that people who faithfully repeat "There is no such
thing as 'wide-angle perspective'--perspective depends solely on
shooting
position" are simply refusing to believe the evidence of their own eyes,
and
refusing to believe it on the basis of some nonsense they have read.
Yes, I
grant you it is widely circulated nonsense, but nonsense all the same.

And what I'm saying is that anybody who looks closely at photos, let
alone actually takes them, quickly learns that it's *true*, and trying
to work on any other basis produces unintended results.

Ordinary people who have not had the dubious benefit of such "learned"
explications can immediately see that most photos taken with a 24mm
lens,
for example, do indeed (when viewed in their entirety) have a wide-angle
perspective.

What you are describing is not perspective.

Of course it is. What else would you call it?

"Jim Townsend" wrote in message
...
Nostrobino wrote:


You are saying that you really cannot see any difference in perspective
between a shot taken with a 24mm lens and one taken with a 200mm lens?
Remarkable.

Both lenses see the same thing. The 200mm lens just sees less.

That's self-contradictory, Jim. If the 200mm lens "just sees less," then it
does not "see the same thing."



Look at it this way.. If you fix a camera on a tripod, then take
a shot with a 24mm lens then another with a 200mm lens, the
24mm lens photo will have a wider field of view.

Note that magnification is nothing more than narrowing field of
view.

Right. So far, so good.


Perspective doesn't change.

Sure it does.



The 200mm lens will see less, but nontheless, it sees the *same*
thing the 24mm lens saw. The perspective is exactly the same.

No, it is not. The perspective in the PART of the 24mm shot that corresponds
to the full 200mm shot DOES have exactly the same perspective. But there is
a lot more to the 24mm shot than that, which you are ignoring. And it's the
additional parts which give it a different perspective.


If you crop an area of the 24mm photo that corresponds to
what you see in the 200mm photo, then enlarge them to the same
size.. They will be exactly the same. This includes the apparent
'space compression'. There's no difference.

Correct. By so cropping it, you have radically changed the perspective.



You can create the effect of a longer lens by cropping. This is
what is happening with the digital zoom offered by consumer digicams.
The only thing that will be different is the depth of field.

As a matter of fact, with 35mm lenses, the term magnification
(as it relates to telescopes and binoculars) is rarely used.
It doesn't show up in manufacturers specs.. All they detail is
the field of view in degrees.

Try this.. Look across the room at an object with one eye
closed. Now take a long roll (like you get with wrapping
paper). Look at the object through the long roll. Doing
this narrows your field of view. Did the perspective change ?

You bet.

Look at it this way:

You will agree with me, will you not, that perspective is a characteristic
of any picture (photo or otherwise) which represents solid objects at
various distances?

Is there ANY part of such a picture (excepting blank spaces of course) which
DOES NOT contribute to its perspective?

No. There is not.

Ergo, once you start cropping the wide-angle shot to make it look like the
long-lens shot, you are throwing out elements which were an important part
of the original perspective.

Any thing "X" from which you remove a substantial part is no longer X.
Logically, this applies to perspective just as much as it does to anything
else. The perspective of any picture is made up of various
elements--vanishing points, parallel lines converging into the distance,
etc. Start throwing out those elements around the edges (as by cropping) and
you are ipso facto changing the perspective.

Again: shots taken with wide-angle lenses DO have a "wide-angle lens look,"
or wide-angle perspective, anyone can see that they do, and no amount of
denial based on specious reasoning (no matter how often published) can
change this.

Take a shot of someone's dining room with a 17mm lens and they will be
impressed by "how much larger it looks!" Wide-angle perspective has
exaggerated the distances. Take a shot of oncoming highway traffic with a
300mm lens and the impression will be "how jammed together all the cars
are!" Telephoto perspective has produced spatial compression. You may deny
these effects all you like, go on insisting that "there is no wide-angle
look or telephoto look," but anyone with eyes can see that they are what
they are.

"David Littlewood" wrote in message
...
[ . . . ]
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.

No, it will look just the same, only with more magnification and a
smaller FOV.

And a Rolls-Royce is just like a Yugo, only with various differences.

Other points already covered elsewhere, redundantly.

"David Littlewood" wrote in message
...
[ . . . ]
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.

No, it will look just the same, only with more magnification and a
smaller FOV.

And a Rolls-Royce is just like a Yugo, only with various differences.

Other points already covered elsewhere, redundantly.

Nostrobino wrote:

Except that the effect is not in any way the result of the focal length of
the lens, but of the magnification.

The magnification IS a direct result of the focal length used.

No, it's not. The magnification is magnification. You can achieve that
magnification in exactly the same way by cropping the field of view.

You are saying that you really cannot see any difference in perspective
between a shot taken with a 24mm lens and one taken with a 200mm lens?

No, I can't, because there isn't any. There is a difference in the field
of view, but that's it.

There is no such thing as a "telephoto look".

You honestly BELIEVE this? Looking at photos taken with 200mm and 300mm
lenses, you would have no clue from their appearance that they'd be taken
with long lenses?

Of course I would, because the field of view will be smaller.

The "look" you are talking about is a product of magnification,

Take a 24mm shot and magnify it all you like, it will never (when viewed in
its entirety) look like a 300mm shot.

Whether it's viewed in its entirety has nothing to do with perspective.

and thus not notice that the parallel lines are doing exactly
the same thing in both pictures.

There is nothing to notice or not notice; many parallel lines in the
wide-angle shot do not even exist in the long-lens shot.

But the ones that do exist are converging exactly as much and in the same
way as the ones in the wide-angle shot.

Parallel lines will not be parallel in a picture unless they are also parallel
to the image plane. Focal length does not affect this. It is a product of
projecting the image onto a flat surface.

Of course it is. This is really the sticking point, as I have indicated
before. When one speaks of any picture as having perspective, it is the
whole picture that one is talking about. If you start zeroing in on smaller
and smaller components of the picture, you not only change the perspective
as you do so but could eventually reach a point where there is no
perspective at all.

No, you don't. There is no change in the perspective, and there will always
be a perspective unless you are talking theoretically about making an image
of a single point in space, something you can't actually do.

and the parallel lines would be the same except that you'd see more of them,

Then they would not be "the same."

Yes, they would be the same. They would not be parallel; they will converge
precisely as much as they do in a wide-angle shot.

and thus be fooled into thinking there is more convergence when in fact
there is not.

The convergence is not really there anyway, i.e. parallel lines do not
converge in a three-dimensional world. It is only the APPEARANCE of
convergence that lends any picture its perspective. It is the exaggerated
convergence of parallels in a wide-angle shot that give it the familiar and
easily seen (no matter how strenuously denied) wide-angle perspective.

A wide-angle shot does not exaggerate the convergence, it merely makes it
more visible. The convergence is exactly the same.

The wide-angle look is a product of the larger field of view, not of the
perspective. The reason things seem to distort at the edges of a wide-
angle image is because you are projecting a spherical image onto a flat
plane,

No, not a spherical image. What is projected onto the flat plane is the
two-dimensional representation of a three-dimensional world. That's
perspective.

You are not understanding how a picture is created. The image is spherical;
that's just how the world works.

Imagine that you are sitting with your head in the center of a transparent
sphere. You can look in any direction and see what is there. You can change
the size of the sphere (by changing the focusing distance of the lens), but
all of the points that are a certain distance from your lens always create a
sphere. When you take a picture, your lens cuts out a section of the sphere,
flattens it, and that becomes the picture. But, since the section that is
cut out is never flat to begin with, you need a method of flattening it.
That's the projection -- same as you need to do when making a map on a flat
piece of paper.

A normal (ie, non-fisheye) lens uses a projection that keeps straight lines
straight, in order to best represent the way humans see the world. A
by-product of this projection is that parallel lines will not remain
parallel; that's the trade-off. This "distortion" does not change with
the lens focal length; the only thing the focal length does is change the
size of the section of the sphere that is cut out. The section remains
the same shape and needs the same distortion in order to flatten it.

A fisheye lens uses a different projection, one that keeps right angles
as right angles. The by-product of that projection is that straight
lines do not remain straight. The perspective, however, is still the
same.

The fisheye lens does project a spherical image (more correctly, an
inside-the-hemisphere image) onto a flat plane. But I don't believe we have
any real disagreement about that, and it's really off the subject of
perspective anyway. Perspective, at least in the classical sense, is only
obtained with (reasonably) rectilinear lenses.

That is not correct. All lenses project a spherical image onto a flat plane
because that's just how it works. Perspective is the same regardless of
what projection is used to create the flat image.

--
Jeremy |

Nostrobino wrote:

Except that the effect is not in any way the result of the focal length of
the lens, but of the magnification.

The magnification IS a direct result of the focal length used.

No, it's not. The magnification is magnification. You can achieve that
magnification in exactly the same way by cropping the field of view.

You are saying that you really cannot see any difference in perspective
between a shot taken with a 24mm lens and one taken with a 200mm lens?

No, I can't, because there isn't any. There is a difference in the field
of view, but that's it.

There is no such thing as a "telephoto look".

You honestly BELIEVE this? Looking at photos taken with 200mm and 300mm
lenses, you would have no clue from their appearance that they'd be taken
with long lenses?

Of course I would, because the field of view will be smaller.

The "look" you are talking about is a product of magnification,

Take a 24mm shot and magnify it all you like, it will never (when viewed in
its entirety) look like a 300mm shot.

Whether it's viewed in its entirety has nothing to do with perspective.

and thus not notice that the parallel lines are doing exactly
the same thing in both pictures.

There is nothing to notice or not notice; many parallel lines in the
wide-angle shot do not even exist in the long-lens shot.

But the ones that do exist are converging exactly as much and in the same
way as the ones in the wide-angle shot.

Parallel lines will not be parallel in a picture unless they are also parallel
to the image plane. Focal length does not affect this. It is a product of
projecting the image onto a flat surface.

Of course it is. This is really the sticking point, as I have indicated
before. When one speaks of any picture as having perspective, it is the
whole picture that one is talking about. If you start zeroing in on smaller
and smaller components of the picture, you not only change the perspective
as you do so but could eventually reach a point where there is no
perspective at all.

No, you don't. There is no change in the perspective, and there will always
be a perspective unless you are talking theoretically about making an image
of a single point in space, something you can't actually do.

and the parallel lines would be the same except that you'd see more of them,

Then they would not be "the same."

Yes, they would be the same. They would not be parallel; they will converge
precisely as much as they do in a wide-angle shot.

and thus be fooled into thinking there is more convergence when in fact
there is not.

The convergence is not really there anyway, i.e. parallel lines do not
converge in a three-dimensional world. It is only the APPEARANCE of
convergence that lends any picture its perspective. It is the exaggerated
convergence of parallels in a wide-angle shot that give it the familiar and
easily seen (no matter how strenuously denied) wide-angle perspective.

A wide-angle shot does not exaggerate the convergence, it merely makes it
more visible. The convergence is exactly the same.

The wide-angle look is a product of the larger field of view, not of the
perspective. The reason things seem to distort at the edges of a wide-
angle image is because you are projecting a spherical image onto a flat
plane,

No, not a spherical image. What is projected onto the flat plane is the
two-dimensional representation of a three-dimensional world. That's
perspective.

You are not understanding how a picture is created. The image is spherical;
that's just how the world works.

Imagine that you are sitting with your head in the center of a transparent
sphere. You can look in any direction and see what is there. You can change
the size of the sphere (by changing the focusing distance of the lens), but
all of the points that are a certain distance from your lens always create a
sphere. When you take a picture, your lens cuts out a section of the sphere,
flattens it, and that becomes the picture. But, since the section that is
cut out is never flat to begin with, you need a method of flattening it.
That's the projection -- same as you need to do when making a map on a flat
piece of paper.

A normal (ie, non-fisheye) lens uses a projection that keeps straight lines
straight, in order to best represent the way humans see the world. A
by-product of this projection is that parallel lines will not remain
parallel; that's the trade-off. This "distortion" does not change with
the lens focal length; the only thing the focal length does is change the
size of the section of the sphere that is cut out. The section remains
the same shape and needs the same distortion in order to flatten it.

A fisheye lens uses a different projection, one that keeps right angles
as right angles. The by-product of that projection is that straight
lines do not remain straight. The perspective, however, is still the
same.

The fisheye lens does project a spherical image (more correctly, an
inside-the-hemisphere image) onto a flat plane. But I don't believe we have
any real disagreement about that, and it's really off the subject of
perspective anyway. Perspective, at least in the classical sense, is only
obtained with (reasonably) rectilinear lenses.

That is not correct. All lenses project a spherical image onto a flat plane
because that's just how it works. Perspective is the same regardless of
what projection is used to create the flat image.

--
Jeremy |

wrote:
On Mon, 02 Aug 2004 05:24:32 -0000, Jeremy Nixon
wrote:

There is no such thing as a "telephoto look". The "look" you are talking
about is a product of magnification,

Don't you realize you are denying the existence of something in one
sentence and in the next one explaining how it was produced? This is
tantamount to saying there is no pregnant look because it is a by
product of sexual intercourse.

Then it's equally valid to say that pregnancy is a "sexual look".

The so-called "telephoto look" is not a product of the lens focal length.
You can get exactly the same "look" by cropping out the center of a wide-
angle picture -- it's magnification, nothing more.

--
Jeremy |

wrote:
On Mon, 02 Aug 2004 05:24:32 -0000, Jeremy Nixon
wrote:

There is no such thing as a "telephoto look". The "look" you are talking
about is a product of magnification,

Don't you realize you are denying the existence of something in one
sentence and in the next one explaining how it was produced? This is
tantamount to saying there is no pregnant look because it is a by
product of sexual intercourse.

Then it's equally valid to say that pregnancy is a "sexual look".

The so-called "telephoto look" is not a product of the lens focal length.
You can get exactly the same "look" by cropping out the center of a wide-
angle picture -- it's magnification, nothing more.

--
Jeremy |

wrote:
On Mon, 02 Aug 2004 05:24:32 -0000, Jeremy Nixon
wrote:

There is no such thing as a "telephoto look". The "look" you are talking
about is a product of magnification,

Don't you realize you are denying the existence of something in one
sentence and in the next one explaining how it was produced? This is
tantamount to saying there is no pregnant look because it is a by
product of sexual intercourse.

Then it's equally valid to say that pregnancy is a "sexual look".

The so-called "telephoto look" is not a product of the lens focal length.
You can get exactly the same "look" by cropping out the center of a wide-
angle picture -- it's magnification, nothing more.

--
Jeremy |

Nostrobino wrote:

Ordinary people who have not had the dubious benefit of such "learned"
explications can immediately see that most photos taken with a 24mm
lens, for example, do indeed (when viewed in their entirety) have a
wide-angle perspective.

What you are describing is not perspective.

Of course it is. What else would you call it?

Field of view.

--
Jeremy |