![]() | This article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||
|
Nice first paragraph, containing:
"... Perspective distortion is determined by the relative distances at which the image is captured and viewed, and is due to the angle of view of the image (as captured) being either wider or narrower than the angle of view at which the image is viewed, hence the apparent relative distances differing from what is expected ..."
That is, according to the definition of distortion, we are comparing input to a system, to output from a system, and in this case, the input is the photographer's viewpoint or perspective, and the output is the audience's viewpoint or perspective of the presentation image.
BUT no one is following that criteria when subsequently exploring conditions where system perspective distortion may be observed, explained, and intentionally employed or avoided if desired.
An image captured with a wide angle lens is not distorted, it can't be, because it is only the system input.
It must be compared to the system output before assessing system distortion, if any.
It must be compared to the experience of the audience of the resulting presentation image, the system output, in order for there to be a discussion of system distortion, in this case, system perspective distortion.
If the audience positions themselves such that they see the presentation image from proportional distance resulting in an identical angle of view to the photographer's capture angle of view, then there is no distortion.
"... But wide angle lenses distort everything, especially close up ...", someone might say.
No, they do not.
If you get close enough to the resulting printed image, relative in distance that the photographer was from the subject, such that the photographer's angle of view and the print-viewer's angle of view are the same, then the audience will have the same experience of the subject, NO DISTORTION.
Please edit subsequent sections from the first paragraph to ALWAYS consider the definition of system distortion as a comparison of input to output.
See also https://www.edmundoptics.com/resources/application-notes/imaging/distortion/ and http://www.parallelhomeaudio.net/TypesAudioDistortion.html which sadly do not grock that they are comparing input to output, duh.
http://www.encyclopedia.com/science-and-technology/computers-and-electrical-engineering/electrical-engineering/distortion DOES mention system input versus output, but cites no author or published source other than the Columbia Encyclopedia, below, I will edit it slightly to be non-system specific ( audio versus imaging ):
"... [ System ] Distortion ... [ is ] undesired change in [ information ] as it passes from the input to the output of some system or device ... [ and ] results in poor reproduction of [ the original information ] ... ..." -- The Columbia Encyclopedia, 6th edition, The Columbia University Press
I will keep searching academic and research materials that are not readily published or accessible on the web.
But, c'mon, folks, stop thinking that something in reality that we can observe without a camera -- someone's nose looking way-big when we put our eye right up to it -- is "Perspective distortion ( photography )" -- we don't need no camera to see big noses up close, that is NOT distortion, that's reality.
Thank you, carry on -- Photographic Fallacy Hunter -- 2600:8806:2400:7E00:2CA4:94D1:6BC:80F1 ( talk) 05:22, 25 June 2017 (UTC)
This article previously claimed that perspective distortion was caused by lens focal length, and it had the title "Perspective distortion caused by lens focal length".
This is factually inaccurate, since perspective distortion of the sort described here ( big noses in portraits, and as shown in the images included in the article ) is a function solely of camera to subject distance. Anyone with a camera and lenses of at least two different focal lengths can do an experiment to demonstrate this.
Confusingly, later material in the article (the text describing the photos included in the article) correctly explained that the effect was caused by camera to subject distance, and that reframing identically with a wider angle lens required placing the camera closer to the subject, thus causing this perspective distortion.
I altered the introductory text to correct the factual inaccuracies. I slightly altered the later text describing the images to increase clarity a little. Then I moved the article so that it would not have a title that was factually incorrect. Then I went through the rest of Wikipedia and updated links so that they point to the new location. I've left a redirect at Perspective distortion caused by lens focal length for the usual reasons, and also because the myth that focal length affects perspective distortion is widely believed, and the article might well be searched for under these terms. Jeff Medkeff | Talk 16:11, Jan 31, 2005 (UTC)
Discussion prior to article move follows:
A close up portrait shot with a, say 24 or 28 mm, compared to a portrait of the same person using a 105 is in my opinon the best example of perspective distortion -- all assuming a 35 mm camera ;-). -- Egil 18:52 Jan 29, 2003 (UTC)
nice addition, Egil. could you explain about "pillow" distortion? I've never heard of it. And, yes, it is a 35mm camera. I'll try the portraits when I next get a chance (probably in late february!) That amateur photographer,
Koyaanis Qatsi
I'm taking the pics back out of the table, as for people with a narrow browser window the table is too wide. By simply sticking them next to each other, we let the browser wrap them into a column -- which is not as satisfying as seeing them in a quad arrangement, but vertical scrolling is much more comfortable for the web reader than horizontal scrolling. -- Brion 19:29 Jan 29, 2003 (UTC)
Please note that the link to "Perspective Distortion: Source," added to the bottom of this article points to a new article in which the Conclusion is at variance with the conclusion with this article. Suggest this page is too flawed for minor editing and be replaced with Perspective Distortion, Source. See link at bottom. Pat Kelso 22:57 CST Jan 30, 2004
The title isn't OK this article is about perspective distortion and not lens distorsion (barrel distortion for instance). Ericd 09:51, 7 Mar 2004 (UTC)
Sorry saw the 'move this page' suggestion too late. Will use in future if my poor brain can retain it that long. But have moved my part of Perspective distortion via cut and paste to Perspective projection distortion ... this to accomodate objection that 'persepctive' can refer to many other things.... Pat Kelso 19:47, Mar 7, 2004 (UTC)
OK I move this one to "Perspective distortion caused by lens focal lenght" Ericd 19:56, 7 Mar 2004 (UTC)
Could also call it "Perspective compression and extension", since this technique can be applied equally well for paintings (although not seen very often).
Perspective distortion should be a pointer to the two articles. Ideally, both should be combined in one article.
--
Egil
Or could the article be called "Perspective change"? --
Egil 20:35, 7 Mar 2004 (UTC)
________________________
re "Some paintings have true perspective according to optical laws while other have faked perspective. Among the interesting case in paintings is "La última cena" from Leonardo da Vinci that as an accurate super-wide perspective did Leonardo get this by geometry reasoning or by a "camera obscura" view ?"
The focal length of a lens has no dilatory effect on perspective, p e r s e. The perspective is always correct for the focal lengths involved. The focal point of a lens is analogous to the station point of perspective projection - a point that may be moved without changing the correctness of a perspective projection. Will leave this posted for few days for comment before incorporating rationale into the article. Pat Kelso 01:53, Mar 25, 2004 (UTC)
Wow, no talk in over 2.5 years. This article could use better photo examples, esp. including something forward of the main subject and some more clearly identifiable background objects whose sizes can be easily noticed. A set of only 2 or 3 in more normal layout should be fine. Dicklyon 18:11, 9 December 2006 (UTC)
Also need photo examples of the distortion appearing in many pictures shot with telephoto lenses and a couple of photo examples of the artistic use of perspective distortion that aren't copyrighted. Anoneditor 02:05, 11 December 2006 (UTC)
I'm not sure I like this new treatment. I'm quite familiar with the traditional 19th-century analysis of "correct perspective" based on the viewing distance compared to the focal length times enlargement factor. But it's been presented here without the enlargement factor, so it makes little sense. Even with enlargement factor, it made only theoretical sense. The alternative is to say that perspective is just the relative size of objects in the scene, and that it can be exaggerated by shooting very close, or distorted the other way by shooting from far away. You might still want to invoke a "normal" viewing distance, but of course it will depend on print size if you do. In practice, I don't think you'll find that the perception of perspective distortion will abate much at all by changing your viewing distance. Geometrically, it makes theoretical sense, but the perception of photos doesn't necessarily follow the simple-minded rules that would make it look that way. Is this treatment following some book? If so, need to cite it. If not, let revert it. Dicklyon 07:23, 11 December 2006 (UTC)
To say that perspective distortion is dependent solely on subject distance is less correct than to say it depends on focal length. Although relative distances of various parts of an image are relevant to perspective distortion, they do not change it. If you change distance to subject and change nothing else about an image, you will not change the perspective distortion (you will change the perspective, but not the distortion), while if you change focal length and change nothing else, you will change perspective distortion (although the effect might now always be obvious).
What perspective distortion is actually dependent on is solely angle of view. When the angle of view is greater than what your eyes would see from the same position you get extension distortion. When it is less than what your eyes would see, you get compression distortion. Changing distance to keep any object in the photo at the same apparent size as it is in another photo with a different angle of view will make the distortion more obvious, but the effect exists with or without the comparison shot. Shooting a photo with a "normal" length lens will make it pretty much impossible to create perspective distortion without changing angle of view somewhere in the post processing or print process.
If perspective distortion were caused solely by distance to subject, you would not need to experiment with two different focal length lenses or cropping images to see a difference in it. Rodrin ( talk) 04:34, 19 November 2008 (UTC)
I see that someone made another edit, and they are on the right track to simplify the first paragraph under the Cause heading. However, I am still not satisfied with it. Now it's nice and simple, but it doesn't really explain why distortion is taking place. "Perspective distortion is caused when the apparent relative distances of objects from the viewer compared to their actual distances change (what it says now, but more specific), but their apparent relative distances from the viewer compared to their surrounding objects remain the same (a simpler and therefore somewhat clearer version of what it said before)." That's probably about as clear as mud. I think I need better wording. Any thoughts? Rodrin ( talk) 18:53, 20 November 2008 (UTC)
Distortion at a wide angle of view occurs with a short focal length, as I've enumerated in the intro paragraph. If you apply the the thin lens (1/X + 1/Y = 1/Z where X is object distance, Y is image distance and Z is focal length) to any focal length, you'll note that objects that are close to the lens will project images much less distance than objects that are far from the lens. For instance, if you were to solve for Y with the formula -1/(1/X - 1/Z) for any focal length, you'll note a curve at closer distances which levels off after a certain distance. A short focal length (such as 10mm) has an extreme curve, meaning that the image of an object .5 feet away will be projected much closer than the image of an object 1 foot away. As this demonstrates, the distance from the lens is one of the contributing factors to perspective distortion. If an object looks normal in a 50mm lens, the object will continue to look normal in a 20mm lens, if the camera and object remain in the same position. It's the repositioning of the camera to maintain the same framing of the object that produces the distortions.
Wide angle lenses (short focal lengths) allow you to see an entire object that is close to the lens, giving the foreshortened appearance. The short focal length is not the direct cause of the distortion, but allows the viewer to readily see the distortion. I want to note that cropping a photo to simulate a longer focal length will produce a more "normal" image. I also want to point out that focal length and angle of view are closely related. Wikipedia's page on angle of view is quoted as saying: "For lenses projecting rectilinear (non-spatially-distorted) images of distant objects, the effective focal length and the image format dimensions completely define the angle of view." Because this is a photography page, it's important to recognize this fact and start to involve the issue of focal length with angle of view. I would like someone to actually post some scientific information or rebut what I'm writing. As it stands there are absolutely NO citations and no consensus in the discussion.
Finally, compression of objects that are far is independent of focal length. The focal length will simply "magnify" what is seen afar and allows someone to see it more readily. As I mentioned above, compression of far objects can be seen on a photo taken with a normal lens, just at a lower resolution. Kakomu ( talk) 20:22, 24 March 2009 (UTC)
The redirect
Perspective Distortion, Source has been listed at
redirects for discussion to determine whether its use and function meets the
redirect guidelines. Readers of this page are welcome to comment on this redirect at
Wikipedia:Redirects for discussion/Log/2023 March 19 § Perspective Distortion, Source until a consensus is reached.
Shhhnotsoloud (
talk)
14:44, 19 March 2023 (UTC)
![]() | This article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||
|
Nice first paragraph, containing:
"... Perspective distortion is determined by the relative distances at which the image is captured and viewed, and is due to the angle of view of the image (as captured) being either wider or narrower than the angle of view at which the image is viewed, hence the apparent relative distances differing from what is expected ..."
That is, according to the definition of distortion, we are comparing input to a system, to output from a system, and in this case, the input is the photographer's viewpoint or perspective, and the output is the audience's viewpoint or perspective of the presentation image.
BUT no one is following that criteria when subsequently exploring conditions where system perspective distortion may be observed, explained, and intentionally employed or avoided if desired.
An image captured with a wide angle lens is not distorted, it can't be, because it is only the system input.
It must be compared to the system output before assessing system distortion, if any.
It must be compared to the experience of the audience of the resulting presentation image, the system output, in order for there to be a discussion of system distortion, in this case, system perspective distortion.
If the audience positions themselves such that they see the presentation image from proportional distance resulting in an identical angle of view to the photographer's capture angle of view, then there is no distortion.
"... But wide angle lenses distort everything, especially close up ...", someone might say.
No, they do not.
If you get close enough to the resulting printed image, relative in distance that the photographer was from the subject, such that the photographer's angle of view and the print-viewer's angle of view are the same, then the audience will have the same experience of the subject, NO DISTORTION.
Please edit subsequent sections from the first paragraph to ALWAYS consider the definition of system distortion as a comparison of input to output.
See also https://www.edmundoptics.com/resources/application-notes/imaging/distortion/ and http://www.parallelhomeaudio.net/TypesAudioDistortion.html which sadly do not grock that they are comparing input to output, duh.
http://www.encyclopedia.com/science-and-technology/computers-and-electrical-engineering/electrical-engineering/distortion DOES mention system input versus output, but cites no author or published source other than the Columbia Encyclopedia, below, I will edit it slightly to be non-system specific ( audio versus imaging ):
"... [ System ] Distortion ... [ is ] undesired change in [ information ] as it passes from the input to the output of some system or device ... [ and ] results in poor reproduction of [ the original information ] ... ..." -- The Columbia Encyclopedia, 6th edition, The Columbia University Press
I will keep searching academic and research materials that are not readily published or accessible on the web.
But, c'mon, folks, stop thinking that something in reality that we can observe without a camera -- someone's nose looking way-big when we put our eye right up to it -- is "Perspective distortion ( photography )" -- we don't need no camera to see big noses up close, that is NOT distortion, that's reality.
Thank you, carry on -- Photographic Fallacy Hunter -- 2600:8806:2400:7E00:2CA4:94D1:6BC:80F1 ( talk) 05:22, 25 June 2017 (UTC)
This article previously claimed that perspective distortion was caused by lens focal length, and it had the title "Perspective distortion caused by lens focal length".
This is factually inaccurate, since perspective distortion of the sort described here ( big noses in portraits, and as shown in the images included in the article ) is a function solely of camera to subject distance. Anyone with a camera and lenses of at least two different focal lengths can do an experiment to demonstrate this.
Confusingly, later material in the article (the text describing the photos included in the article) correctly explained that the effect was caused by camera to subject distance, and that reframing identically with a wider angle lens required placing the camera closer to the subject, thus causing this perspective distortion.
I altered the introductory text to correct the factual inaccuracies. I slightly altered the later text describing the images to increase clarity a little. Then I moved the article so that it would not have a title that was factually incorrect. Then I went through the rest of Wikipedia and updated links so that they point to the new location. I've left a redirect at Perspective distortion caused by lens focal length for the usual reasons, and also because the myth that focal length affects perspective distortion is widely believed, and the article might well be searched for under these terms. Jeff Medkeff | Talk 16:11, Jan 31, 2005 (UTC)
Discussion prior to article move follows:
A close up portrait shot with a, say 24 or 28 mm, compared to a portrait of the same person using a 105 is in my opinon the best example of perspective distortion -- all assuming a 35 mm camera ;-). -- Egil 18:52 Jan 29, 2003 (UTC)
nice addition, Egil. could you explain about "pillow" distortion? I've never heard of it. And, yes, it is a 35mm camera. I'll try the portraits when I next get a chance (probably in late february!) That amateur photographer,
Koyaanis Qatsi
I'm taking the pics back out of the table, as for people with a narrow browser window the table is too wide. By simply sticking them next to each other, we let the browser wrap them into a column -- which is not as satisfying as seeing them in a quad arrangement, but vertical scrolling is much more comfortable for the web reader than horizontal scrolling. -- Brion 19:29 Jan 29, 2003 (UTC)
Please note that the link to "Perspective Distortion: Source," added to the bottom of this article points to a new article in which the Conclusion is at variance with the conclusion with this article. Suggest this page is too flawed for minor editing and be replaced with Perspective Distortion, Source. See link at bottom. Pat Kelso 22:57 CST Jan 30, 2004
The title isn't OK this article is about perspective distortion and not lens distorsion (barrel distortion for instance). Ericd 09:51, 7 Mar 2004 (UTC)
Sorry saw the 'move this page' suggestion too late. Will use in future if my poor brain can retain it that long. But have moved my part of Perspective distortion via cut and paste to Perspective projection distortion ... this to accomodate objection that 'persepctive' can refer to many other things.... Pat Kelso 19:47, Mar 7, 2004 (UTC)
OK I move this one to "Perspective distortion caused by lens focal lenght" Ericd 19:56, 7 Mar 2004 (UTC)
Could also call it "Perspective compression and extension", since this technique can be applied equally well for paintings (although not seen very often).
Perspective distortion should be a pointer to the two articles. Ideally, both should be combined in one article.
--
Egil
Or could the article be called "Perspective change"? --
Egil 20:35, 7 Mar 2004 (UTC)
________________________
re "Some paintings have true perspective according to optical laws while other have faked perspective. Among the interesting case in paintings is "La última cena" from Leonardo da Vinci that as an accurate super-wide perspective did Leonardo get this by geometry reasoning or by a "camera obscura" view ?"
The focal length of a lens has no dilatory effect on perspective, p e r s e. The perspective is always correct for the focal lengths involved. The focal point of a lens is analogous to the station point of perspective projection - a point that may be moved without changing the correctness of a perspective projection. Will leave this posted for few days for comment before incorporating rationale into the article. Pat Kelso 01:53, Mar 25, 2004 (UTC)
Wow, no talk in over 2.5 years. This article could use better photo examples, esp. including something forward of the main subject and some more clearly identifiable background objects whose sizes can be easily noticed. A set of only 2 or 3 in more normal layout should be fine. Dicklyon 18:11, 9 December 2006 (UTC)
Also need photo examples of the distortion appearing in many pictures shot with telephoto lenses and a couple of photo examples of the artistic use of perspective distortion that aren't copyrighted. Anoneditor 02:05, 11 December 2006 (UTC)
I'm not sure I like this new treatment. I'm quite familiar with the traditional 19th-century analysis of "correct perspective" based on the viewing distance compared to the focal length times enlargement factor. But it's been presented here without the enlargement factor, so it makes little sense. Even with enlargement factor, it made only theoretical sense. The alternative is to say that perspective is just the relative size of objects in the scene, and that it can be exaggerated by shooting very close, or distorted the other way by shooting from far away. You might still want to invoke a "normal" viewing distance, but of course it will depend on print size if you do. In practice, I don't think you'll find that the perception of perspective distortion will abate much at all by changing your viewing distance. Geometrically, it makes theoretical sense, but the perception of photos doesn't necessarily follow the simple-minded rules that would make it look that way. Is this treatment following some book? If so, need to cite it. If not, let revert it. Dicklyon 07:23, 11 December 2006 (UTC)
To say that perspective distortion is dependent solely on subject distance is less correct than to say it depends on focal length. Although relative distances of various parts of an image are relevant to perspective distortion, they do not change it. If you change distance to subject and change nothing else about an image, you will not change the perspective distortion (you will change the perspective, but not the distortion), while if you change focal length and change nothing else, you will change perspective distortion (although the effect might now always be obvious).
What perspective distortion is actually dependent on is solely angle of view. When the angle of view is greater than what your eyes would see from the same position you get extension distortion. When it is less than what your eyes would see, you get compression distortion. Changing distance to keep any object in the photo at the same apparent size as it is in another photo with a different angle of view will make the distortion more obvious, but the effect exists with or without the comparison shot. Shooting a photo with a "normal" length lens will make it pretty much impossible to create perspective distortion without changing angle of view somewhere in the post processing or print process.
If perspective distortion were caused solely by distance to subject, you would not need to experiment with two different focal length lenses or cropping images to see a difference in it. Rodrin ( talk) 04:34, 19 November 2008 (UTC)
I see that someone made another edit, and they are on the right track to simplify the first paragraph under the Cause heading. However, I am still not satisfied with it. Now it's nice and simple, but it doesn't really explain why distortion is taking place. "Perspective distortion is caused when the apparent relative distances of objects from the viewer compared to their actual distances change (what it says now, but more specific), but their apparent relative distances from the viewer compared to their surrounding objects remain the same (a simpler and therefore somewhat clearer version of what it said before)." That's probably about as clear as mud. I think I need better wording. Any thoughts? Rodrin ( talk) 18:53, 20 November 2008 (UTC)
Distortion at a wide angle of view occurs with a short focal length, as I've enumerated in the intro paragraph. If you apply the the thin lens (1/X + 1/Y = 1/Z where X is object distance, Y is image distance and Z is focal length) to any focal length, you'll note that objects that are close to the lens will project images much less distance than objects that are far from the lens. For instance, if you were to solve for Y with the formula -1/(1/X - 1/Z) for any focal length, you'll note a curve at closer distances which levels off after a certain distance. A short focal length (such as 10mm) has an extreme curve, meaning that the image of an object .5 feet away will be projected much closer than the image of an object 1 foot away. As this demonstrates, the distance from the lens is one of the contributing factors to perspective distortion. If an object looks normal in a 50mm lens, the object will continue to look normal in a 20mm lens, if the camera and object remain in the same position. It's the repositioning of the camera to maintain the same framing of the object that produces the distortions.
Wide angle lenses (short focal lengths) allow you to see an entire object that is close to the lens, giving the foreshortened appearance. The short focal length is not the direct cause of the distortion, but allows the viewer to readily see the distortion. I want to note that cropping a photo to simulate a longer focal length will produce a more "normal" image. I also want to point out that focal length and angle of view are closely related. Wikipedia's page on angle of view is quoted as saying: "For lenses projecting rectilinear (non-spatially-distorted) images of distant objects, the effective focal length and the image format dimensions completely define the angle of view." Because this is a photography page, it's important to recognize this fact and start to involve the issue of focal length with angle of view. I would like someone to actually post some scientific information or rebut what I'm writing. As it stands there are absolutely NO citations and no consensus in the discussion.
Finally, compression of objects that are far is independent of focal length. The focal length will simply "magnify" what is seen afar and allows someone to see it more readily. As I mentioned above, compression of far objects can be seen on a photo taken with a normal lens, just at a lower resolution. Kakomu ( talk) 20:22, 24 March 2009 (UTC)
The redirect
Perspective Distortion, Source has been listed at
redirects for discussion to determine whether its use and function meets the
redirect guidelines. Readers of this page are welcome to comment on this redirect at
Wikipedia:Redirects for discussion/Log/2023 March 19 § Perspective Distortion, Source until a consensus is reached.
Shhhnotsoloud (
talk)
14:44, 19 March 2023 (UTC)