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01-15-2012, 11:37 AM   #166
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QuoteOriginally posted by vonBaloney Quote
I understand focal length here (which compresses or expands space perpendicular to the film plane), but not crop. Cropping doesn't change the distances (or apparent distances) between anything. Just more or less stuff is visible.
So a 55mm lens on a 4x5 and APS camera will give the same perspective? No. The same if I crop the 4x5 down to APS.

01-15-2012, 11:40 AM   #167
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QuoteOriginally posted by alohadave Quote
I don't believe you, but if you can show me two pictures taken from two different positions that show the same perspective, I'll not comment on it again.
Don't shot the messager. And why do I have to do your work? Especially since this is not exactly a secret. But I will show you how.

Take two objects and photograph one at 2ft and one 4ft from the camera and then photograph them at 5ft and 10ft from the camera. Their relative size will be the same. And please post them so other can see.
01-15-2012, 12:04 PM   #168
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QuoteOriginally posted by Yamanobori Quote
So a 55mm lens on a 4x5 and APS camera will give the same perspective? No. The same if I crop the 4x5 down to APS.
But the common area between the two is unchanged, no? Nothing in that inner box (APS area) looks different, and the objects within it appear the same distances from each other in either format. Revealing more or less of the circle the lens projects doesn't change what it projects.
01-15-2012, 02:20 PM   #169
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QuoteOriginally posted by Yamanobori Quote
Don't shot the messager. And why do I have to do your work? Especially since this is not exactly a secret. But I will show you how.
You have to prove it because you are making the claim. It is your responsibility as the one making the claim to back it up.

QuoteOriginally posted by Yamanobori Quote
Take two objects and photograph one at 2ft and one 4ft from the camera and then photograph them at 5ft and 10ft from the camera. Their relative size will be the same. And please post them so other can see.
Obviously you don't understand what I'm talking about. If you take a picture with two different camera formats, like your 4x5 and APS-C example a couple posts up, from the same spot, the perspective of the two pictures will be identical. The APS-C will be cropped much tighter than the 4x5 picture, but other than that, they will show the same perspective. Enlarging the cropped picture will not change the perspective of the picture.

If you are talking about filling the frame with your subject so that it is the same relative size on both formats, your perspective will still have changed because you have to change your position to do so (assuming that you are shooting with a prime or set focal length - a zoom lens would allow you to change your framing, but your perspective wouldn't change). Your subject will be the same relative size, but all other elements of the scene will have shifted when you moved.

01-15-2012, 05:00 PM   #170
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QuoteOriginally posted by alohadave Quote
You have to prove it because you are making the claim. It is your responsibility as the one making the claim to back it up.
Sorry, not my claim. This is rather basic stuff regarding perspective.

QuoteQuote:
Obviously you don't understand what I'm talking about. If you take a picture with two different camera formats, like your 4x5 and APS-C example a couple posts up, from the same spot, the perspective of the two pictures will be identical. The APS-C will be cropped much tighter than the 4x5 picture, but other than that, they will show the same perspective. Enlarging the cropped picture will not change the perspective of the picture.
Actually, I believe I explained that. Since both those pictures will be presented the same size, the cropped image will be magnified in relation to the uncropped image. This has the effect of displacing the infinity point or points in linear perspective. If you change the position of those points, you change the perspective. This is really a basic concept. We perceive the pictures as originating at different infinity points. That will give each picture different perspective--we will see one having great depth and one having compressed depth..

The ratio of image sizes does not carry enough information to define perspective in an image.
01-15-2012, 05:13 PM   #171
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QuoteOriginally posted by vonBaloney Quote
But the common area between the two is unchanged, no? Nothing in that inner box (APS area) looks different, and the objects within it appear the same distances from each other in either format. Revealing more or less of the circle the lens projects doesn't change what it projects.
But you are not going far enough. That inner area will be enlarged a greater degree to the 4x5 area to make the same display size--and yes, display size is important. You would be right in saying the objects contained within the APS frame would have the same image-size ratio, but we are looking now at two different images. Perspective is the appearance of depth in a 2-D image and the 4x5 image will have a greater feeling of space than the crop. In regards to linear perspective, the lines in each image do not recede to the same infinity point anymore. It is well know in drafting that displacing the infinity points change perspective.

But you have seen this. Take a simple landscape or seascape with a horizon. We really can't change the distance to the horizon, but a wide angle shoot will have a different perspective than a telephoto one. The wide angle gives a very different feeling of space than the telephoto (cropped) image, even though the horizon line and a point in front of it can be in both images.

Seeing is believing.
01-15-2012, 06:23 PM   #172
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QuoteOriginally posted by Yamanobori Quote
But you are not going far enough. That inner area will be enlarged a greater degree to the 4x5 area to make the same display size--and yes, display size is important. You would be right in saying the objects contained within the APS frame would have the same image-size ratio, but we are looking now at two different images. Perspective is the appearance of depth in a 2-D image and the 4x5 image will have a greater feeling of space than the crop. In regards to linear perspective, the lines in each image do not recede to the same infinity point anymore. It is well know in drafting that displacing the infinity points change perspective.
But then you are not comparing apples to apples because the pictures will then have different content. Doesn't it matter what is in that extra area of the larger format in terms of your subjective experience of it?

And what does "a greater feeling of space" exactly mean? How do I get a greater feeling of space when the display size is equal? If I move in the 4x5 to take an "equivalent" photo of what's in the crop, have I gained that greater space back?
01-15-2012, 06:36 PM - 2 Likes   #173
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QuoteOriginally posted by Yamanobori Quote
This a common mistake. Linear perspective comes from a ratio of object distances--you can two picture at two different object distances and achieve the same linear perspective. Since we think of an image as one thing, what is foreground and background changes when you change focal length or crop. Since the ratio of foreground to background distance changes, so does the perspective of the image--landscapes have very different perspectives because of focal length simply because of that. (The ratio of objects in the frame do not change, but a picture is more than some arbitrary choice of objects, but you still can change distance to those same objects and maintain the same perspective or image size ratio and so this is a relative problem, not and absolute one.)

The other way to think of this is that the focal length or crop changes the final magnification of the image--we think of display size is constant. In two point perspective, displacing the points changes perspective. Change in magnification has the same effect.

The great thing is, you can actually see this effect in your photography.


This is news to me as well.

As far as I've ever heard or read, distance to subject is the only thing that affects perspective. I wonder if you're talking about something besides the standard definition of perspective... Convergence, maybe?

Consider these crops of different focal lengths, all taken from the same distance to subject and cropped to gain the same framing. Note the relationship between the subject and the background elements - there is no change, because the distance to subject did not change.







^^ Taken from this link.

Here's another descriptive article on perspective, from ---> luminous landscape.



Perhaps you can show some images that illustrate what you're talking about, or provide a link, I'd like to know more and especially would like to know if my understanding of perspective is in need of update.



.


Last edited by jsherman999; 01-15-2012 at 06:53 PM.
01-15-2012, 06:55 PM   #174
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QuoteOriginally posted by vonBaloney Quote
But then you are not comparing apples to apples because the pictures will then have different content. Doesn't it matter what is in that extra area of the larger format in terms of your subjective experience of it?

And what does "a greater feeling of space" exactly mean? How do I get a greater feeling of space when the display size is equal? If I move in the 4x5 to take an "equivalent" photo of what's in the crop, have I gained that greater space back?
Perspective is a subjective attribute.

Take a picture of a room with a 16mm lens and a 60mm lens. Which gives you a great sense of space? It has been know for a great deal of time that telephotos compress space and wide angles expand it.
01-15-2012, 07:02 PM   #175
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QuoteOriginally posted by vonBaloney Quote
I understand focal length here (which compresses or expands space perpendicular to the film plane), but not crop. Cropping doesn't change the distances (or apparent distances) between anything. Just more or less stuff is visible.
The only thing that changes is the enlargement size relative to the scale of the viewer. There are two radial points out on the horizon that defines the perspective of an object relative to the viewer. When you enlarge the crop you are, as was stated by another poster, displacing the two radial points relative to the observer - they get farther apart which 'flattens' out the perspective because the image is fixed. When you change the distance to subject you also change the distance between the two radial points on the horizon - they get closer together [if the subject is kept at a similar compositional size] and have the opposite affect.

In addition: Objects that are closer to infinity have radial lines that are more lateral than front/back [the further they are from center] and as such the perspective appears flatter. As in telephoto as opposed to a wide-angle.

Last edited by bossa; 01-15-2012 at 07:13 PM.
01-15-2012, 07:03 PM   #176
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QuoteOriginally posted by Yamanobori Quote
Take a picture of a room with a 16mm lens and a 60mm lens. Which gives you a great sense of space? It has been know for a great deal of time that telephotos compress space and wide angles expand it.
Yes, I know that and mentioned it above somewhere. But that effect is NOT subjective -- meaning it is an optical property of a given focal length lens (compared to some other one) and not just dependent on some feeling/perception in the viewer. The space compression and expansion properties of telephoto and wide angle lenses will still "happen" whether or not there is a viewer at all. Are these properties that what you mean what you say a "sense of space"? Because again, if we are talking about a crop of a larger image we are talking about the same lens from the same position -- therefore there is no compression or expansion of space within the chosen area. (It is just cropped.) And display size does not affect this. You can't get a "long lens effect" just by making your display size bigger or smaller.

So I'm still confused what you're referring to with "greater sense of space".
01-15-2012, 07:03 PM   #177
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QuoteOriginally posted by bossa Quote
Like I said earlier, it's relative to scale and viewing distance. If you crop out some information and enlarge the output then the relationship to the viewer changes because there's a different context and scale of reference. I won't bother to respond to your remarks re' my education or competency.
With respect, you are comparing two unrelated things.
01-15-2012, 07:06 PM   #178
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QuoteOriginally posted by bossa Quote
The only thing that changes is the enlargement size relative to the scale of the viewer. There are two radial points out on the horizon that defines the perspective of an object relative to the viewer. When you enlarge the crop you are, as was stated by another poster, displacing the two radial points relative to the observer - they get farther apart which 'flattens' out the perspective because the image is fixed. When you change the distance to subject you also change the distance between the two radial points on the horizon - they get closer together and have the opposite affect.
So in this model, when the display size changes, the viewer must remain in the same spot? (When in a museum, I stand farther away from canvases that are 20ft x 40ft than I do from ones that are 2ft x 4ft.)
01-15-2012, 07:09 PM   #179
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QuoteOriginally posted by Yamanobori Quote

Take a picture of a room with a 16mm lens and a 60mm lens. Which gives you a great sense of space? It has been know for a great deal of time that telephotos compress space and wide angles expand it.
Actually,, that's not true at all, it's common vernacular for what you think you're seeing, but a telephoto does not actually 'compress' space any more than am equivalent crop of a WA lens would.

Look at the two links I provided - they talks about that very concept.

From this article:

"Because many photographers, including many who have had a lot of experience making photographs, believe that a long focal length lens "compresses" elements of a scene at different distances from the camera, and that a short focal length lens will "distort" a scene, they also believe that these sorts of perspective problems can be corrected merely by changing the focal length of the lens used. These ideas are all absolutely false."



From the LL article:

First is 200mm:


Second is an aggressive crop of 24mm, taken from the exact same location:


Last edited by jsherman999; 01-15-2012 at 07:14 PM.
01-15-2012, 07:20 PM   #180
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QuoteOriginally posted by jsherman999 Quote
This is news to me as well.

As far as I've ever heard or read, distance to subject is the only thing that affects perspective. I wonder if you're talking about something besides the standard definition of perspective... Convergence, maybe?

Consider these crops of different focal lengths, all taken from the same distance to subject and cropped to gain the same framing. Note the relationship between the subject and the background elements - there is no change, because the distance to subject did not change.

BTW, the ratio of image sizes for elements in the image do not change, only perspective.







^^ Taken from this link.

Here's another descriptive article on perspective, from ---> luminous landscape.



Perhaps you can show some images that illustrate what you're talking about, or provide a link, I'd like to know more and especially would like to know if my understanding of perspective is in need of update.



.
Now put all three uncropped images in the post at the same time. The 24mm will have greater perspective--it will also show more. Like I said, this is not simply image-size ratio which does not define perspective by itself. What you have most likely learnt is that the ratio of image size is directly proportional to the ratio of object distances. But that is not down to one distance, but a ratio

Here is one image with the cropped image next to it. It clearly shows the linear perspective, how fast the radial lines converge, are not the same. We will perceive the image on the left as having greater perspective or space or depth or whatever subjective term you would like..
Attached Images
 

Last edited by Yamanobori; 01-15-2012 at 07:41 PM.
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