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10-22-2009, 03:39 PM   #31
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QuoteOriginally posted by Eruditass Quote
Correct me if I'm wrong, but if you print the crop at the same size as the un-cropped longer focal length image and viewed them at the same distance they would appear the same. Certainly, to get a certain complete frame and perspective, you need a certain focal length, but that's not what I'm getting at..

I suppose we have different definitions of "distortion"
I'm referring to the very specific type of distortion called "perspective distortion", which is defined by the type of comparison I outlined. it's called perspective distortion if objects in the print appear bigger or smaller than they appear in real life. If you print the crops, then either they *all* have perspective distortion, or none of them do - because they all show the same FOV. As it happens, that FOV is a relatively narrow one, so the answer is they *all* show perspective distortion. That is, they *all* show the sign looking much larger than it did in real life. Is that "distortion" in any other sense? No, but it fits the definition of perspective distortion.

You might be wondering why this is considered distortion at all, and I sympathize, but that's what it's called. And it can lead to some interesting optical illusions.

10-22-2009, 03:43 PM   #32
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QuoteOriginally posted by newarts Quote
A long lens enlarges background items and a short lens enlarges foreground items.
The *only* extent to which this is true is the extent to which you change your position. If you kept the same position in both shots, you'd find the backgreound and foreground *both* got larger - and by the same amount - when you switched from short to long lenses.

Your example demonstrates very nicely the effect of changing your position, though, and of course the change in focal length is what prompted you to change your position.

Which is why "zooming with your feet" is a misnomer. Using your feet changes perspective; using a zoom does not!
10-22-2009, 04:57 PM   #33
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Marc, I'd rather you used "correct" than "true." The former suggests a mistake of ignorance which, after reading your post, I have to agree with (even if I don't know for sure what I did); the latter a fabrication meant to deceive and that certainly wasn't the case. I might be slow, but I don't lie about it.

Still and all, I take your point. I'd like to do an experiment, but I can't figure out how to record what I see (I guess I could sketch it by hand?) and what the lens sees for contrast,
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10-22-2009, 05:08 PM   #34
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QuoteOriginally posted by newarts:
A long lens enlarges background items and a short lens enlarges foreground items.
QuoteOriginally posted by Marc Sabatella Quote
The *only* extent to which this is true is the extent to which you change your position. If you kept the same position in both shots, you'd find the backgreound and foreground *both* got larger - and by the same amount - when you switched from short to long lenses.

Your example demonstrates very nicely the effect of changing your position, though, and of course the change in focal length is what prompted you to change your position.

Marc, That's true but I argue that since one requires the other, they are equivalent.

Distance, focal length, magnification, and perspective are connected mathematically. If you want the same magnification (ie subject size in the frame) at a different focal length you must change the distance, hence change the perspective. They are connected and equivalent.

This is semantic dancing I suppose. The following illustration of perspective geometry of shows why:


I think this is an easy to understand illustration of how perspective works. Note that the illustration says NOTHING about the lens in the camera. Move the camera closer to the picture plane and the arrow's projection on the picture plane gets higher compared to the mountain's.

So what is "normal"? I think it is a concept related to our mental database of images: looking at a photo that contains a person and a horse, I'll bet most people will make a judgment about their relative positions in space by using the size of the person as the basis for measurement.

If an A4 print is almost filled by a person's face, the observer's mind says "aha! the face is large therefore I am not far from the person - therefore that tiny horse must be very far away indeed!" Here the observer makes assumptions based on his/her individual "normal" mental image database.

This implies to me that the OP's feeling the red line in the image posted would better represent reality is based on his mental remembrance of a scene originally viewed from a greater distance (look at the above schematic: as the camera is moved to the left, the light ray from the mountaintop to the camera gets closer to overlaying that from the arrowhead.) In his mind he "knows" the mountains are bigger compared to the pole.

Unfortunately, our mental database of remembered images is distorted by their content; the field of view we use while building a mental image of our lover's face is likely different than the field we use while building a memory of a maggot munching on meat. So which fov is normal?


Last edited by newarts; 10-23-2009 at 03:56 AM.
10-22-2009, 05:11 PM   #35
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Dave, if this is correct "...a long lens enlarges background items and a short lens enlarges foreground items" does that mean that a "normal" lens does neither? Put another way, if a normal lens records what you "saw," then the notion that the background mountain in my example is larger is reality than it is in the image is just in my perception?

So to return to my original question, which lens will record that reality most faithfully?

Reality, faith, photography, what concepts,
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10-22-2009, 07:46 PM   #36
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QuoteOriginally posted by CFWhitman Quote
The example that you share here only proves that fact number one is true (Changing focal length does not change the relationship of the the sizes of objects in the photo compared to each other). Remember that cropping a photo changes its angle of view just as switching focal length changes the angle of view (as I said). So if you change to a wider angle of view by using a shorter focal length, and then crop the photo back to the angle of view that you changed from, you haven't affected perspective distortion at all (or, you've changed it and then changed it back). Cropping the photo is the same thing as using a smaller sensor; it changes the relationship between the focal length and the image size. It's this relationship that is important.
I'm well aware of what you are talking about but I would not call that perspective or "telephoto" distortion. That is a misnomer. What wouldn't be a misnomer is calling it an optical illusion. Apply a term "distortion" to a physical term "focal length" does not make sense because of all the other variables - print size, sensor size, etc. The way you are portraying it is that it is inherently linked to focal length, focal length inherently brings about this distortion.
QuoteQuote:

Remember too that I said that perspective distortion was akin to an optical illusion, so there may not be "real distortion" in the sense that you mean. What these example pics all do exhibit, since the shorter focal length shots have been cropped to a very narrow angle of view, is compression distortion (sometimes called "telephoto" distortion). Everything in the photos looks like it's right on top of each other because the angle of view makes it appear as if the viewpoint were closer than it really was. From the actual viewpoint, the objects in the picture were all relatively close together. When you make it appear as though the viewpoint were much closer than it really was, then the objects appearing to be relatively close together seems "wrong" because if you were really that close, then the objects would be relatively further apart. It's not how far away the objects are that makes their appearance seem wrong; it's how much closer they appear to be than they really are.
Yes, makes it look like. It doesn't distort anything, it simply magnifies the perspective change - a natural thing, not anything related to "distortion" or "to twist awry or out of shape; make crooked or deformed".
QuoteQuote:

The author of the pdf that you cite goes through a lot of math to prove that perspective exists and that it is relative. I have gone through the math before, but I didn't need to do so to know this. He proves these things, and then he proceeds to draw the wrong conclusions by his proof, because he is clinging to the same false premise that I stated above, that perspective distortion is caused by changing the relationship of the sizes of objects in the photo. In reality perspective distortion is caused by not changing that relationship while seeming to change the viewpoint.
The whole point of my posts is that you are needless complicating and (not purposefully) misleading people with your terminology. By your definition of perspective distortion, every print is distorted unless it is at the right angle. Any magnification at all is an abnormal distortion. All I am trying to clear up is that focal length does not "cause" distortion just by itself.
QuoteQuote:

For practical purposes the author may not be likely to encounter a situation where it matters whether his understanding is correct or not, but this is the problem I see with it. By changing focal lengths or otherwise changing the angle of view of a photo, you can make the same two objects photographed from the same place appear to be closer together than they really are, or farther apart than they really are. His understanding of perspective distortion either does not allow for this, or glosses over it without explaining it.
You can do the same by moving a print back and forth. Move it back far enough and the two objects inside look just like real life distance relationship wise. Moving it closer makes it seem like they are next to each other. The message I am trying to convey is that focal length doesn't breed perspectives that you can't already get in one fashion or form. There may be limits on sensor size, pixel density, print size, but it is not all tied to focal length only.

QuoteOriginally posted by Marc Sabatella Quote
I'm referring to the very specific type of distortion called "perspective distortion", which is defined by the type of comparison I outlined. it's called perspective distortion if objects in the print appear bigger or smaller than they appear in real life. If you print the crops, then either they *all* have perspective distortion, or none of them do - because they all show the same FOV. As it happens, that FOV is a relatively narrow one, so the answer is they *all* show perspective distortion. That is, they *all* show the sign looking much larger than it did in real life. Is that "distortion" in any other sense? No, but it fits the definition of perspective distortion.

You might be wondering why this is considered distortion at all, and I sympathize, but that's what it's called. And it can lead to some interesting optical illusions.
Thank you, that was driving me nuts. Instead of that huge post before, someone could've just defined "perspective distortion" - which I did put in quotes in the beginning because I know what the effect is, but don't consider it a distortion but a simple and normal log distance maping function which is displayed all around us, just look at the focus ring's markings. I am 100% sure it misleads half the people that learn about it.

Last edited by Eruditass; 10-22-2009 at 08:12 PM.
10-23-2009, 12:02 PM   #37
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QuoteOriginally posted by FHPhotographer Quote
Marc, I'd rather you used "correct" than "true."
Point taken; although I didn't mean to imply you were being untruthful in that sense. Sorry about that.

QuoteQuote:
Still and all, I take your point. I'd like to do an experiment, but I can't figure out how to record what I see (I guess I could sketch it by hand?) and what the lens sees for contrast,
As someone who came (back) to photography from painting, it's pretty natural for me to want to use a sketch to resolve these, but if you're OK with chimping the LCD as a way of gauging what the camera "saw" (as opposed to waiting until you see it larger at home), I'd just do some spot checks. Like seeing how high the mountain came on the telephone pole, where along each power line the mountain intersected it, use an object in your outstretched arm as a measuring stick to check the relative sizes of objects in the scene.

But really, do that if you wish to convince yourself of this empirically, but this isn't like a focus test where you do it because there is anydoubt about the outcome. Unless you live in some sort of alternate non-Euclidean universe, these things *will* pan out as I have said. These have been fundamental principles in linear perspective as practiced by artists for about 500 years, scientifically proven and empirically observed over and over.
10-23-2009, 12:22 PM   #38
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QuoteOriginally posted by newarts Quote
Marc, That's true but I argue that since one requires the other, they are equivalent.
One only requires the other if you wish to keep some given object in the scene (and it will be *only* one object - or at least, only objects at one given distance) the same size. Which is indeed a valid way of wanting to look at things; it's just not, I think, what was being discussed. Although actually, in a way, it was - assuming that Brian was accurately describing the apparent position of the mountains with his red line, then it had to have been a change in distance (or viewpoint height) that accounts for the discrepancy. But of course, that change would have been inadvertent, not induced by a change in focal length, and simply changing lenses (or zooming - I keep forgetting about that! :-) without changing position would not have altered the relative height of the mountains and power lines.

The drawing in your post does indeed nicely illustrate how subject distance affects linear perspective.

QuoteQuote:
So what is "normal"? I think it is a concept related to our mental database of images: looking at a photo that contains a person and a horse, I'll bet most people will make a judgment about their relative positions in space by using the size of the person as the basis for measurement.

If an A4 print is almost filled by a person's face, the observer's mind says "aha! the face is large therefore I am not far from the person - therefore that tiny horse must be very far away indeed!" Here the observer makes assumptions based on his/her individual "normal" mental image database.
Yes, and you're basically describing the concept of perspective distortion here. The way the numbers work out, if you shoot with a "normal" lens and view that print from a "typical" viewing distance, the visual cues you see regarding the relative sizes of the person and horse will lead you to the correct conclusion about how distant that horse is. But if you take the picture from a greater distance using a long telephoto lens, yielding the same sized face in the print, the horse will appear larger in comparison, making you think the horse is closer to the person than it is.

This is actually the best picture I have to illustrate how deceptive can be, although I don't know that it will trigger the same reponse in anyone else that it does in me. You have to take my word for it that this is actually a fairly large stage, and the three musicians pictured were not *nearly* close enough to touch each other. But I'm far enough away from the stage that the *relative differences* in my distances to each are not as great as they'd be if I were standing closer and shooting with a wider angle lens to get the pianist a similar size. As result, the musicians appear close to the same size, making them look to be in close proximity:



This was shot at 135mm, and was obviously cropped some too (to make it square). I'm actually only a few yards away from the pianist, but it's enough to create a much different sense of perspective than this image, shot in the same location with musicians positioned fairly similarly:



Here, the singer standing in the background is actually quite a bit closer to the pianist than the drummer was in the first shot, but he appears much smaller in comparison, because the *relative difference* in my distances to each has become smaller - I'm now only couple of feet from the pianist.

The second image here as actually taken at 70mm, so there is some perspective distorition here too - the singer is actually a bit further way than he appears. Had I shot with a "normal" lens (and come in closer to get the pianist to look the same size), the singer would have looked smaller and more distant still. And if I get the chance to shoot that configuration with the DA15 I'm expecting on Monday (!), I'd be shooting from extremely close to the pianist, and the singer would like he was in the next room entirely.


Last edited by Marc Sabatella; 10-23-2009 at 12:30 PM.
10-23-2009, 02:50 PM   #39
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I would like to say that I don't think this is complicated at all. It seems very simple to me, and the only reason that I go to such great lengths to explain it is that people don't seem to get it.

First, some groundwork. You don't really need to consciously know all this to have a working understanding of this subject, but it helps to combat the botched explanation of this that I see all over the place.

You should be aware of the concepts of Zeeman's Paradox and ordinary, or normal viewing distance.

Zeeman's Paradox says that "There is only one point in front of a perspective drawing where its three mutually perpendicular vanishing points appear in mutually perpendicular directions, but such a drawing nonetheless appears realistic from a variety of distances and angles." In other words, a perspective drawing (or a photograph) only has correct perspective from one viewpoint, but our brain has no trouble seeing it as correct when we view it from many other points. More on this below.

"Normal viewing distance," or "ordinary viewing distance" is basically the concept that for any given photo or drawing (or other two dimensional image) there is a single point at which people tend to view it, or at least interpret it. For rectangular images that aren't much larger in one dimension than the other (square, 3x2, 4x3, etc.), this point is considered to be somewhere near the same length as the diagonal of the image. Why this is the case is open to debate, but that it is the case is generally accepted from experience.

Zeeman's Paradox is older than photography. What photography taught us about Zeeman's Paradox, however, is that the point at which we interpret a perspective drawing or a photograph is not necessarily the point at which perspective becomes correct (where the drawing looks right) as the Paradox states, but rather is basically the same point for any drawing of the same dimensions; thus we have the concept of "normal viewing distance."

The concept of "normal viewing distance" has its limits. If we look at a perspective drawing or photo from an extreme distance (near or far) or display it at an extreme size (large or small) it can affect our perception of its perspective. However, within reasonable limits it will not do so (or at least not more than very subtly).

What this boils down to is that under most circumstances the viewpoint at which we interpret photographs can be considered a constant, the "normal viewing distance," and even if we view a photo from a different point we still tend to interpret it from that point.

The existence of the normal viewing distance is the reason for the concept of the "normal" lens. The perspective for any photograph will appear correct when the ratio of the focal length to sensor (or film) size is equal to the ratio of viewing distance to print size. If you accept the concept of normal viewing distance, then a normal lens will have about the same 1:1 ratio of focal length to sensor diagonal as viewing distance to print diagonal. Any very significant departure from that ratio will significantly alter our perception of its perspective.

QuoteOriginally posted by Eruditass Quote
I'm well aware of what you are talking about but I would not call that perspective or "telephoto" distortion. That is a misnomer. What wouldn't be a misnomer is calling it an optical illusion. Apply a term "distortion" to a physical term "focal length" does not make sense because of all the other variables - print size, sensor size, etc. The way you are portraying it is that it is inherently linked to focal length, focal length inherently brings about this distortion.
I did not make up the term perspective distortion; that is what this effect is generally called. Also, calling it "telephoto" distortion (or "wide angle" distortion for the opposite effect) is generally considered questionable. The terms "compression distortion" and "extension distortion" are generally favored.

Calling this an optical illusion would be questionable as well. I said it was akin to an optical illusion, but it's not exactly the same thing as an optical illusion (at least, no more so than photography in general). In other words, if you want to interpret "optical illusion" broadly, then, we're talking about photography here -- photographs are all optical illusions.

I didn't say that perspective distortion was inherent to focal length; I said that it was about angle of view. I said that changes in focal length always caused changes in perspective distortion unless they were compensated for by other changes that affected angle of view.

QuoteQuote:
Yes, makes it look like. It doesn't distort anything, it simply magnifies the perspective change - a natural thing, not anything related to "distortion" or "to twist awry or out of shape; make crooked or deformed".
The reason that it is referred to as distortion is because it causes objects to appear to be a different shape than they actually are. When you photograph something through a normal lens and interpret it from the normal viewing distance, then it appears to be the same shape as it really was. When you photograph it through a lens that is significantly longer or shorter and interpret it from the normal viewing distance, then (barring crops or stitches) it appears to be compressed or extended. The distortion is not so much distortion as compared to the the scene viewed from the actual viewpoint (although you could argue that magnification is a type of distortion), but rather distortion as compared to the scene viewed from the apparent viewpoint.

QuoteQuote:
The whole point of my posts is that you are needless complicating and (not purposefully) misleading people with your terminology. By your definition of perspective distortion, every print is distorted unless it is at the right angle. Any magnification at all is an abnormal distortion. All I am trying to clear up is that focal length does not "cause" distortion just by itself.
It's not my terminology. I didn't make this stuff up. Actually, according to this concept only prints that appear to be distorted when interpreted from the normal viewing distance (or at the very least the intended viewing distance) exhibit perspective distortion. But yes, any significant magnification, either greater than 1:1 or less than 1:1, is considered to create perspective distortion.

I am trying to clear up that changing distance to subject by itself does not cause perspective distortion. Changing distance and changing nothing else will not alter this effect, while changing focal length and nothing else will always alter this affect. That is the problem with the incorrect explanation of perspective distortion you can find in many places on the Net. What is misleading is to say that changing distance affects perspective distortion and changing focal length does not. The people who just "know" that using a long lens or a wide angle lens creates perspective distortion are far more correct than all these misguided explanations, because at least changing focal length has a direct influence on angle of view, the real cause of perspective distortion, whereas changing distance does not.

QuoteQuote:
You can do the same by moving a print back and forth. Move it back far enough and the two objects inside look just like real life distance relationship wise. Moving it closer makes it seem like they are next to each other. The message I am trying to convey is that focal length doesn't breed perspectives that you can't already get in one fashion or form. There may be limits on sensor size, pixel density, print size, but it is not all tied to focal length only.
It's tied to angle of view, which is influenced by focal length as well as other factors. However, according to the concept of normal viewing distance, moving the print back and forth doesn't really affect it significantly until you go to extremes. Alterations of angle of view at the capture end are of far more importance.

The idea that perspective distortion is a product of distance (rather than angle of view or magnification) is what is misleading. Everyone who presents this explanation expects you to believe one or more of these incorrect ideas:

Perspective distortion does not really exist. (Whether you think the term is apropos or not, the effect does exist.)

Perspective distortion only exists if you compare two different shots from different distances at different focal lengths (This one is laughable; the effect does not depend on a comparison shot; comparison shots just make it more obvious.)

Perspective distortion is altered by distance to subject. (It is not; perspective is altered by distance, but not perspective distortion; although, of course, it is easier to see the effect in objects closer than those farther away.)

Perspective distortion cannot be altered by changes in focal length. (Changes in focal length always affect perspective distortion unless compensated for by other changes in angle of view.)

There may be others that don't come to mind right now.
10-24-2009, 12:07 AM   #40
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QuoteOriginally posted by CFWhitman Quote
The idea that perspective distortion is a product of distance (rather than angle of view or magnification) is what is misleading.
I agree it's misleading, but I'd put different spin on this than you are. While it's true that perspective distortion is not a product of distance, the issue of distance does play into the effect, because one of the effects of perspective distortion is fooling your eyes into thinking an object depicted was at a different distance than it really was.

QuoteQuote:
Perspective distortion only exists if you compare two different shots from different distances at different focal lengths (This one is laughable; the effect does not depend on a comparison shot; comparison shots just make it more obvious.)
Right. You wouldn't need the comparison shot at all to recognize the perspective distortion if you also had access to the original scene, or if you were really good at unraveling the perspective clues in an image. In my example above, it is obvious to *me* that the first pictures shows perspective distortion, since I know the musicians were not as close together as the picture makes them appear. But other observers might not realize this and think this really is a picture taken with a normal lens of musicians who were standing very close together. If you are sufficiently clever, you might be able to work out from other visual cues in the picture that this is not the case, without reference to the original scene or another picture for comparison (such as by checking vanishing points if you find parallel lines). But comparison pictures help make it clear just what the perspective distortion is.

QuoteQuote:
Perspective distortion is altered by distance to subject. (It is not; perspective is altered by distance, but not perspective distortion; although, of course, it is easier to see the effect in objects closer than those farther away.)
True - the perspective distortion inherent in shooting a given angle of viewing doesn't go away or change if you shoot from a different distance. But again, it's the perception of distance that contributes to the illusion. Shooting telephoto from far away produces a primary subject the same size as shooting normal from closer or wide from closer still, and it's the inability of the eye to figure out that this is that happened that creates the illusion. In the absence of other clues, the eye assumes a picture was shot with a normal lens and gauges what it thinks is the distance to the primary subject, and then interprets the size and position of other objects accordingly.

At least, that's my understanding.
10-24-2009, 11:28 AM   #41
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newarts, you lost me with this statement "This implies to me that the OP's feeling the red line in the image posted would better represent reality is based on his mental remembrance of a scene originally viewed from a greater distance ... In his mind he "knows" the mountains are bigger compared to the pole." I'll grant the line I hastily drew on the image was incorrect and led the discussion off on a tangent, but I don't agree that I'm recalling the scene as viewed from a greater distance than the point at which the photograph was taken. I just went back out to the site to make sure I wasn't mis-remembering, and I still see one thing while the camera records it differently.

Since what I saw, and what I photographed, were from the same position, then the position of the camera isn't as variable, and viewing distance of the image (on screen or printed) is also not a variable. That leaves the lens and the perspective it imposes on the image as the one variable. That brings me back to the original question: if I want to capture the image as seen, do I use a wider-than-35 lens or a narrower-than-35 (telephoto) lens? Or will the answer forever be, "it depends" ?
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10-24-2009, 01:31 PM   #42
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QuoteOriginally posted by FHPhotographer Quote
newarts, you lost me with this statement "This implies to me that the OP's feeling the red line in the image posted would better represent reality is based on his mental remembrance of a scene originally viewed from a greater distance ... In his mind he "knows" the mountains are bigger compared to the pole." I'll grant the line I hastily drew on the image was incorrect and led the discussion off on a tangent, but I don't agree that I'm recalling the scene as viewed from a greater distance than the point at which the photograph was taken. I just went back out to the site to make sure I wasn't mis-remembering, and I still see one thing while the camera records it differently.

Since what I saw, and what I photographed, were from the same position, then the position of the camera isn't as variable, and viewing distance of the image (on screen or printed) is also not a variable. That leaves the lens and the perspective it imposes on the image as the one variable. That brings me back to the original question: if I want to capture the image as seen, do I use a wider-than-35 lens or a narrower-than-35 (telephoto) lens? Or will the answer forever be, "it depends" ?
Brian
If the camera was at the same height as your eyes, the relative heights of the pole and mountains cannot have differed so far as geometric optics is concerned.

Go back there with a tripod, level the camera, point it at the pole and take photos at different focal lengths without moving the tripod. The height of the mountain divided by the height of the pole in the various photos will be identical regardless of focal length.

The only way the mountain's apparent height will grow compared to the pole's height is if you back away from the pole. I think my earlier sketch demonstrates the geometric optics involved.

The angles of the light rays coming from the top of the mountain and top of the pole have nothing to do with the lens in the camera or in your eye. Your visual perception of the relative heights of the two starts with the angles between the light rays. Your mind may have massaged this info somehow to affect what you remembered, but it couldn't have changed the actual geometry.

I'll try to make a photographic demonstration of this.

Dave in Iowa

Last edited by newarts; 10-24-2009 at 01:36 PM.
10-24-2009, 01:43 PM   #43
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I agree with everything you said in your post. I don't mean to give the impression that distance is a subject unrelated to perspective distortion. It's just that the idea that, "far objects are compressed; near objects are extended," is not correct as stated. "Objects farther than you make them appear to be are compressed; objects nearer than you make them appear to be are extended," works (I know you know this). The object's absolute distance is immaterial; it's only its distance relative to your altered perception of its distance that matters.

The people who prove that perspective is relative are not talking about an unrelated subject either, but perspective being relative only makes perspective distortion possible; it doesn't cause it. Of course, people already know that perspective is relative, but those that prove it explain how it works, and the how is interesting and useful to your understanding. The proof however, does nothing to directly explain the perspective distortion effect.

It's like explaining how combustion works to inform people why a building burned down. It explains why it's possible; it doesn't explain why it happened. People already know that combustion exists; explaining how it works might be interesting, but that's not what they want to know. They want to know what started the fire. When these people say, 'a telephoto lens doesn't cause compression distortion; it merely reveals the effect caused by distance,' it's sort of like an arsonist saying, 'I didn't burn the building down; my incendiary device merely revealed the combustible nature of the wood.' Wood being combustible doesn't make a building burn down, and perspective being relative doesn't make perspective distortion happen.

Last edited by CFWhitman; 10-24-2009 at 05:28 PM.
10-24-2009, 02:12 PM   #44
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Dave, I really only had one question in the OP, but I may have not stated it well, so let me rephrase that question: if I'm standing at point X and looking at several objects clustered around point Y, and I take a photograph that shows a different relationship of the Y objects than the relationship I see, and assuming that the 35mm I am using is a "normal" lens, do I need to use a +normal or a -normal lens to be replicate the objects relationship that I see?
Brian
10-24-2009, 02:22 PM   #45
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QuoteOriginally posted by Marc Sabatella Quote
This is actually the best picture I have to illustrate how deceptive can be, although I don't know that it will trigger the same reponse in anyone else that it does in me. You have to take my word for it that this is actually a fairly large stage, and the three musicians pictured were not *nearly* close enough to touch each other. But I'm far enough away from the stage that the *relative differences* in my distances to each are not as great as they'd be if I were standing closer and shooting with a wider angle lens to get the pianist a similar size. As result, the musicians appear close to the same size, making them look to be in close proximity:



This was shot at 135mm, and was obviously cropped some too (to make it square). I'm actually only a few yards away from the pianist, but it's enough to create a much different sense of perspective than this image, shot in the same location with musicians positioned fairly similarly:



Here, the singer standing in the background is actually quite a bit closer to the pianist than the drummer was in the first shot, but he appears much smaller in comparison, because the *relative difference* in my distances to each has become smaller - I'm now only couple of feet from the pianist.

The second image here as actually taken at 70mm, so there is some perspective distorition here too - the singer is actually a bit further way than he appears. Had I shot with a "normal" lens (and come in closer to get the pianist to look the same size), the singer would have looked smaller and more distant still. And if I get the chance to shoot that configuration with the DA15 I'm expecting on Monday (!), I'd be shooting from extremely close to the pianist, and the singer would [look] like he was in the next room entirely.
I think that these photos illustrate the effect fairly well, even though there are no direct comparison shots.

We've been talking about linear perspective here, but in particular your second shot got me to wondering how much of an effect the accommodation perspective cue of the singer being out of focus has on us psychologically. Does the extent to which he is out of focus make up at all for the perspective distortion and help us to feel that he is about as distant as he actually was? I don't know that there is a solid answer to this question; it's just something to ponder over.
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