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03-14-2012, 08:39 AM   #31
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Yes ! I think it is has been established lol

03-14-2012, 09:21 AM   #32
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QuoteOriginally posted by Farmer_Terry Quote
So yes, perspective does depend entirely on where you stand, but yes, lens length does affect perceived perspective. Two different things.
Yes, but the point is, it is *not* the lens focal length that determines this - it is the *field of view* of the lens. Thus, the effect a 50mm lens has on perceived perspective when viewing a print is *different* depending on sensor size. A 50mm is normal on FF, short telephoto on APS-C, but wide angle on 645 format. And thus, images from that exact same lens will have *entirely different effects* on the perceived perspective in the print depending on what camera it is mounted to.

In other words, your previous statement...

QuoteQuote:
If I put the same 50mm lens in front of 35mm film and an APS-C sensor surely the perspective in the both resulting images remains the same
... is just *incorrect*. The effect you refer to is *not* specific to the focal length of the lens but to the FOV it produces on the camera you have it mounted to. Thus, it is a 35mm lens on APS-C that would have the same effect on perceived perspective in the print that 50mm has on FF, because both have the same FOV. A 50mm lens on APS-C would have the same effect on perceived perspective in the print that a 75mm lens would on FF, because both have the same FOV.

For that matter, you could have the same discussion without reference to cameras or lenses, but just talking about drawing or painting. A scene depicted with a given FOV has the same effect on perceived perspective whether that depiction was created by an FF camera with a 75mm lens, an APS-C camera with a 50mm lens, or an artist with a pencil. It's all about FOV, not "focal length", which has no meaning for the case of the artist with the pencil.
03-14-2012, 12:26 PM   #33
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QuoteOriginally posted by Farmer_Terry Quote
So yes, perspective does depend entirely on where you stand, but yes, lens length does affect perceived perspective. Two different things.
First off what is perceived perspective really try to look that term up since it doesn't exist.


Here comes the problem in all of this.

Lets take a photo of a plant, 30cm away with a nice 12mm lens so you see the flowers around it, super right =]
Now lets put on a 100mm macro and shoot the ladybug that's on the flower but we stay at 30cm distance.
Now if we both print to images just as large so that the viewing distance of the photo is the same, then according to you the 12mm photo will have a different perspective than the 100mm macro photo.
Did i understand this correctly?

Last edited by Anvh; 03-14-2012 at 12:32 PM.
03-14-2012, 12:31 PM   #34
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QuoteOriginally posted by westmill Quote
Yes ! I think it is has been established lol
Then why say this?

I was just pointing out that in practicality focal lengh
does indeed give at least the appearence of changing
perspective, which I think is actualy more relevent.


I really don't understand what you say there so please do your best to explain it better because not even RioRico seem to get it so i ain't the only one...

03-14-2012, 11:10 PM   #35
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QuoteOriginally posted by Anvh Quote
Lets take a photo of a plant, 30cm away...
Now if we both print to images just as large so that the viewing distance of the photo is the same, then according to you the 12mm photo will have a different perspective than the 100mm macro photo.
Did i understand this correctly?
That seems to be what he's saying.

QuoteOriginally posted by Anvh Quote
I really don't understand what you say there so please do your best to explain it better because not even RioRico seem to get it so i ain't the only one...
Oh, I get it, yes I do. It's just incorrect.

Think of 'perspective' as a binary function, either this or not-this. We either see one perspective, or we see something else, not a copy. No perspective 'appears' to be another perspective -- each perspective just IS. And just what IS perspective? Hmm, before answering that, I should review my old graphics-engineering texts, or otherwise refresh myself on perspective math.

Or I could stumble on with this: Perspective is the relationship of objects in a scene viewed from a specific point. But that description lacks equations and numbers. Good explanations have equations and numbers. I'll work on that when I wake up.

Last edited by RioRico; 03-14-2012 at 11:16 PM.
03-15-2012, 03:38 AM   #36
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From wiki, hopefully it was what you're looking for.

As objects become more distant they appear smaller because their visual angle decreases. The visual angle of an object is the angle subtended at the eye by a triangle with the object at its base. The greater the distance of the object from the eye, the greater is the height of this triangle, and the less the visual angle. This follows simply from Euclidean geometry.

where h is the apparent height, d is the distance of the object, and a is the actual size of the object.

If an object were actually touching the eye, thus being no distance away, it would appear infinitely tall.
03-15-2012, 09:08 AM   #37
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QuoteOriginally posted by Anvh Quote
First off what is perceived perspective really try to look that term up since it doesn't exist.
The technical term for the effect being discussed is "perspective distortion", and yes, there is a wikipedia entry for it. Simply put, it is what happens if the angle subtended by the print when viewed from a given position differs from the angle of view depicted. If the depicted angle is wider than the angle subtended by the print, the effect is that object look smaller / further away / further apart than they actually are. If the depicted angle is narrower than the angle subtended by the print, the effect is that objects look larger / closer / closer together than they actually are.
03-15-2012, 10:04 AM   #38
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QuoteOriginally posted by Marc Sabatella Quote
The technical term for the effect being discussed is "perspective distortion", and yes, there is a wikipedia entry for it. Simply put, it is what happens if the angle subtended by the print when viewed from a given position differs from the angle of view depicted. If the depicted angle is wider than the angle subtended by the print, the effect is that object look smaller / further away / further apart than they actually are. If the depicted angle is narrower than the angle subtended by the print, the effect is that objects look larger / closer / closer together than they actually are.
Again... thank you
Im not that technical to put it in those terms lol
I did think I had explained it adaquitly enough for
anyone to understand though.
Its pretty basic knowledge for any photographer.
Or so i thought !

03-15-2012, 11:21 AM   #39
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QuoteOriginally posted by Marc Sabatella Quote
The technical term for the effect being discussed is "perspective distortion", and yes, there is a wikipedia entry for it. Simply put, it is what happens if the angle subtended by the print when viewed from a given position differs from the angle of view depicted. If the depicted angle is wider than the angle subtended by the print, the effect is that object look smaller / further away / further apart than they actually are. If the depicted angle is narrower than the angle subtended by the print, the effect is that objects look larger / closer / closer together than they actually are.
Well yes that's what we are talking about but all sources say it's about the distance not the lens focal length.

http://en.wikipedia.org/wiki/Perspective_distortion_(photography)
QuoteQuote:
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.
Distortion It's better to read it on the site with the photos but here is the text.
QuoteQuote:
Perspective

The perspective of a photograph is determined by the viewpoint that the photographer takes in relation to the subject. Nearby subjects are rendered larger than faraway subjects of the same size, which can lead to a sense of depth or convergence of lines that are parallel in object space. A well-known example of a perspective effect are the converging verticals that occur when a building is photographed with a tilted camera. Perspective is not affected by the lens focal length: it depends on the viewpoint only.

The designation 'perspective distortion' is frequently encountered to describe converging verticals and other manifestations of the perspective, but this is questionable as it unjustly suggests a misrepresentation of the reality. A perspective control lens, which is a device that can can be used to 'correct' converging verticals, creates an illusion of a different perspective, but if anything it's the perspective control lens that presents an unnatural perspective, not the normal picture taking lens. (Strictly speaking a PC lens does not correct anything. Its large image circle and mechanical design merely allow a shift of the image to put the subject into the film frame. The prerequisite for nonconverging verticals is that the film plane is kept parallel to the building.)

Converging verticals often encounter psychological resistance, while photographs with converging horizontals such as a road that narrows toward the horizon are readily accepted or even considered as perspective art. Apart from the appreciation by the audience, however, there is no fundamental difference between the two cases.

Another so-called form of distortion is 'geometric distortion', which arises when a three-dimensional object is projected on a plane such as a digital sensor. For instance, a sphere in the image center is rendered as a round disk on the film, while a sphere in the image periphery of a lens with a large angle of view is elliptically elongated. People in the corners of a wideangle image are deformed and may occasionally be saddled with the typical 'egg face'. This geometric effect is a natural consequence of the projection obliquity; the use of the word distortion wrongly suggests an imaging anomaly.

In contrast to optical distortion, perspective and geometric distortions are no lens aberrations. The apparent anomaly is emphasized by a wrong viewpoint for the image. Ideally each photograph should be viewed from a viewpoint that corresponds to the viewpoint of the photographer in relation to the captured scene. A telephoto image should be viewed from far and a wideangle photograph from close. A photograph with converging verticals looks more natural from a low viewpoint, and, similarly, egg faces improve when the photograph is viewed from close. Unfortunately the human eye does not cover a sufficiently large angle to view the entire image of a wideangle lens from nearby, so in practice the viewer takes a distance, notices the deformation, and speaks of distortion.
03-15-2012, 12:55 PM   #40
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QuoteQuote:
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.
A problem with this description is apparent when we look at macro and long tele images. Either will have extremely narrow AOVs, the images captured at distances far from our usual viewpoint. We hominids also have rather different AOVs with both eyes open and with one eye shut. Our one-eye / normal-lens AOV is about 50 degrees, while binocular vision is about 160 degrees. (The lens equivalents on my K20D would be about 30mm [monocular] and 2.6mm [binocular].) So if this model is correct, UWA distortion should be remediable by opening both eyes. Sorry, that 10mm shot still looks abnormal.
03-15-2012, 03:12 PM   #41
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English isn't my first language so maybe i read it wrong.
I was more thinking about the AOV of the subject compared to the viewer.
To keep it simple, the subjects is so high and is such distance away, you can with this make a triangle between the base, the top of the subject and your eyes (camera).
I believe what they call AOV is the angle of your eyes (camera) in that sentence.
It works out when you for example print the photo, it doesn't matter how large you print but the perspective will be "correct" as long as the AOV of the viewer will be the same for the subject as it was for the camera.

Not sure if that is what Wiki means but this how i understand it how they wrote it because they where talking about the warping of an object (the subject) the sentence before that.
03-15-2012, 05:21 PM   #42
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QuoteOriginally posted by Anvh Quote
Well yes that's what we are talking about but all sources say it's about the distance not the lens focal length.
Read the quotes from Wikipedia again, and note the use of the phrase "angle of view". That's proportional to focal length for any given sensor size.
03-15-2012, 11:13 PM   #43
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It's obvious to me from all of the discussions on here about perspective that people continually try to make it fit into their currently held understanding/view of it and no amount of discussion seems to change things.

Perspective, as I understand it, is defined as the way an image intersects a flat image plane and thus translates 3d into a 2d representation. To say that this doesn't change is bizarre because the scale of the image plane relative to the environment and viewer has a definite impact along with the projection device. A super-wide angle lens projecting an image onto the same image plane as a telephoto lens is altering the scale of the perceived environment in relation to the viewer thus altering that viewers 'perspective' or viewpoint. As one poster has already stated, you'd have to have your face right on top of that wide-angle view to get a similar 'perspective' to the tele shot. So print size changes all of these things and the 'distortion' of perspective relative to the viewer changes. Just because all the lines can be extended outwardly doesn't mean that the perspective is the same. It's the scale of the projection in relation to the viewer that changes the relativity of it. I don't for one minute believe the perspective of a macro shot where a fly is seen to be 10" in size or 10' in size depending upon the scale of the projection is the same perspective as a landscape covering miles. The scale is completely different and thus so is the perspective.

Linear perspective can be represented having numerous or few radial points from which forms are constructed. These are clearly different geometrically but it is the viewer's perception which makes them matter - the viewer has to learn how to read all forms of spacial representation because none of them are natural, are abstractions and part of a 2D iconography.

I can't really think of another way of explaining this right now.. but I thought I'd chuck in my thoughts all the same.
03-16-2012, 04:09 AM   #44
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QuoteOriginally posted by Marc Sabatella Quote
Read the quotes from Wikipedia again, and note the use of the phrase "angle of view". That's proportional to focal length for any given sensor size.
They say this 4 sentences later...
Note that perspective distortion is caused by distance, not by the lens per se – two shots of the same scene from the same distance will exhibit identical perspective distortion, regardless of lens used.


So what is it???
This article is so badly written, just like the Bokeh one, it's full with mistakes....
03-16-2012, 04:15 AM   #45
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QuoteOriginally posted by bossa Quote
As one poster has already stated, you'd have to have your face right on top of that wide-angle view to get a similar 'perspective' to the tele shot.
But this isn't correct though per se.
The thing with wide angle lenses is that you often move closer then with a tele-photo lens and that's what makes the difference in perspective not the focal length.

I'll do a simple test later today just to get it over with...


Found these, not the perfect example or the way i wanted it to do but it will do.

One is 28mm lens but cropped
other is 135mm lens, do your best to pick the right one.
Or better yet tell me where the perspective is different between these two.




Last edited by Anvh; 03-16-2012 at 04:44 AM.
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