DoF and Perspective Revisited

[cmi]

I believe that the true underlying topic of this thread is the relationship between pink shrimps penis lenght and climate change in sub-tropical Russia. But I have been wrong before.

Cheers,
Bernard

I meant it serious...

[Ray]

They would be different crops but feature the same perspective, unless we all agree that the definition of the word perspective needs to be changed it might be wise to stick to its currently accepted definition.

Think of a world where some people use the word "pink shrimp" as meaning "great white shark" while others would use "great white shark" when they mean "corruption in sub-tropical Russia". Wouldn't that be confusing?

Cheers,
Bernard

Here's the Wikipedia definition of perspective.

"The two most characteristic features of perspective are that objects are drawn:

Smaller as their distance from the observer increases
Foreshortened: the size of an object's dimensions along the line of sight are relatively shorter than dimensions across the line of sight."

How can you compare the distance and size of objects in one image, taken with a wide-angle lens, with the distance and size of the same objects that don't exist in another image taken with a telephoto lens from the same position?

Size and distance are relative terms. 2mm is meaningful because it is twice the lenth of 1 mm and 1mm is a defined distance. An object is large in relation to another object that is smaller, but not large in relation to another object which is larger. If the smaller object doesn't exist in the image, because the image was taken with a long lens, then we have no sense of the size and distance of the larger object. The perspective in the two different images cannot therfore be the same.

[Panopeeper]

I meant it serious...

Well, the OP mentions two distinct subjects: DoF and perspective.  DoF was not contested, but mixing perspective with FoV or framing is pretty regular.

I have not participated in the predecessor of this thread, but I think the underlying issue is, that some MFDB owners feel (IMO unnecessarily) to have to justify their decisions and spendings by a mystic quality of MFDB shots, namely the "3-D look". This quality is often mentioned but it has never been explained yet. I guess the "differerent perspective" of the very wide angle of view with large formats is supposed to substantiate the "3-D look".

In fact, the look of an image with wide ange is very different from others due to the different perspective, but the perspective difference is not caused by the lens itself but by the different position of the camera.

[Panopeeper]

Ray,

sometimes I have the feeling that you are being obtuse for the sake of obtuseness.

[Ray]

In fact, the look of an image with wide ange is very different from others due to the different perspective, but the perspective difference is not caused by the lens itself but by the different position of the camera.

Can't you see a contradiction is that statement, Gabor? Are you saying that the look of an image with wide angle is only very different from others if the distance to subject is different?

[Ray]

Ray,

sometimes I have the feeling that you are being obtuse for the sake of obtuseness.

Can't help that. I'm actually trying to reconcile two concepts here; the objective performance of the lens and the subjective impression of the viewer.

I would prefer a definition along the lines, 'Any lens used with any camera, from a given position, whatever the focal length and camera format, is potentially capable of delivering the same perspective in the image with either an appropriate amount of cropping, or an appropriate amount of stitching.'

[Panopeeper]

Can't you see a contradiction is that statement, Gabor? Are you saying that the look of an image with wide angle is only very different from others if the distance to subject is different?

There is no contradiction there. Like framing with different focal lengths can be achieved only from different positions, thus the second quoted sentence is meaningless regarding a single shot.

However, if stitching is acceptable, then one can create a compound image with the identical framing and identical perspective as the single, WA shot shows.

I would prefer a definition along the lines, 'Any lens used with any camera, from a given position, whatever the focal length and camera format, is potentially capable of delivering the same perspective in the image with either an appropriate amount of cropping, or an appropriate amount of stitching.'

This "definition" is a consequence of the actual definition of "perspective", thus there is no reason to include it in the definition.

Btw, watch out with "any lens"; this is true only re rectilinear lenses (although the warping by a stitcher can make a fisheye image rectilinear, but let's not go so far).

[Ray]

This "definition" is a consequence of the actual definition of "perspective", thus there is no reason to include it in the definition.

Indeed it is, but I think the definition is necessary to exclude absurd situations. A definition that perspective has nothing to do with focal length, only distance to the subject, can lead one to either absurdities or situations that just appear incorrect to the viewer.

All definitions of 'perspective' that I've seen, refer to the relative sizes of objects in the scene according to distance. Here's one such definition, "the faculty of seeing all the relevant data in a meaningful relationship: Your data is admirably detailed but it lacks perspective."

I would maintain that a single shot with a 100mm lens may be admirably detailed, but could be perceived as lacking the perspective of a single shot from the same distance using a 24mm lens on the same camera. This is because the wider-angle shot includes more detail. That additional detail of recognisable and smaller objects in the background, and larger objects in the foreground, provides the visual clues as to perspective within the image.

Definitions should be able to stand on their own as being correct.

Btw, watch out with "any lens"; this is true only re rectilinear lenses (although the warping by a stitcher can make a fisheye image rectilinear, but let's not go so far).

Good point!

[JeffKohn]

Any 17mm shot on a 35mm camera, of a scene at a specified distance will give one a different perspective of the scene than a 40mm shot of the same scene from the same distance, simply by virtue of the fact it is a different image with a wider field of view.

You are intermingling the concepts of FOV and perspective. Nobody is disputing that a 17mm shot gives you a wider field of view. I'm not disputing the 17mm and 40mm images will be different, simply because the 40mm shot is a fairly small crop of the 17mm shot. In fact if you read my original post, I specifically said that the "wide angle effect" was a matter of perspective (camera location) and field of view:

Rectilinear distortion has everything to do with perspective and field of view. Note I said field of view, not focal length. Whether you get that perspective and field of view from a single wide-angle shot or by shooting several shots with a longer lens and then stitching them using a rectilinear projection, the resulting perspective will be the same.

And in fact, the whole point of the original question that started this thread, was whether you would get the same "wide-angle" effect of a single shot with a wide lens, by shooting the same scene with multiple shots from a longer lens and then stitchign them with pano software. My point was yes it's possible, because it's the camera position and field of view that matter, not the focal lenght. I stand by that statement, and Bernard even showed a real-world example that corroborates this.

[BernardLanguillier]

I meant it serious...

Sorry Christian, couldn't resist.    Being serious is something I am simply not capable of in the world we live in... or is it solemn that I cannot be? http://www.ted.com/index.php/talks/paula_s...ts_serious.html

Cheers,
Bernard

[elf]

I would maintain that a single shot with a 100mm lens may be admirably detailed, but could be perceived as lacking the perspective of a single shot from the same distance using a 24mm lens on the same camera. This is because the wider-angle shot includes more detail. That additional detail of recognisable and smaller objects in the background, and larger objects in the foreground, provides the visual clues as to perspective within the image.

Now, you're saying the exact opposite of what reality is.  A 100mm lens will resolve more and therefore have more detail than a 24mm lens (assuming the quality of the lens are comparable). The 24mm lens will have a larger FOV than the 100mm, but equal sized FOV crops from either lens will have the same perspective and will only differ in the amount of detail and DOF. It doesn't matter if you're comparing single frames or stitched frames.  The images posted earlier in this thread demonstrate this principal quite well.

[Ray]

Now, you're saying the exact opposite of what reality is.  A 100mm lens will resolve more and therefore have more detail than a 24mm lens ...

But that's more or less exactly what I said. This is what I wrote:  "I would maintain that a single shot with a 100mm lens may be admirably detailed".

...equal sized FOV crops from either lens will have the same perspective and will only differ in the amount of detail and DOF.

Of course! That's a tautology. The same focal length of lens on the same format of camera will will produce an image of the same FoV (from the same distance) which will therefore have the same perspective. Detail will depend on sensor pixel density, and DoF will depend on F stop.

What I'm arguing against is the simplistic notion that perspective has nothing to do with focal length, period. Such a statement has to be qualified along the lines, 'provided the FoV of the resulting image is the same'. You can get that result by either cropping or stitching, depending on camera format. If you don't crop or stitch, then perspective is not just dependent upon distance to subject, but also on the focal length of lens used.

It needs to be mentioned.

[Ray]

You are intermingling the concepts of FOV and perspective.

Yes I am, because I see them in all my images as being intermingled. Images with extensive FoV will tends to have greater, more obvious, more clearly defined perspective.

Lenses with a short focal length tend to have a wide FoV, and used from the same distance as a longer focal length, will tend to produce a greater perspective than the longer lens, as a result of their wider FoV.

[elf]

Yes I am, because I see them in all my images as being intermingled. Images with extensive FoV will tends to have greater, more obvious, more clearly defined perspective.

Lenses with a short focal length tend to have a wide FoV, and used from the same distance as a longer focal length, will tend to produce a greater perspective than the longer lens, as a result of their wider FoV.

This is just silly, how do you explain the images in post #23 of this thread.  When stitching is involved there is no defined FOV for a particular focal length.  The FOV will be whatever you want it to be. Your definition of perspective is not the commonly accepted definition.

[Panopeeper]

What I'm arguing against is the simplistic notion that perspective has nothing to do with focal length, period. Such a statement has to be qualified along the lines, 'provided the FoV of the resulting image is the same'.

Ray,

I again (still?) have the feeling that you are being obtuse for the sake of obtuseness. You must be bored.

[Dick Roadnight]

Members who only wish to read constructive comments...

...you can set your profile to ignore named users, so that their posts do not appear on your computer... you just get a message asking you if you want to "Un-ignore" them.

I suggest the the word "perspective" should not be used without qualification. e.g. "view point perspective".

The phrase "focal length " should only be used in relation to a specific format, and if you are writing about Field Of View (angle) then use the term FOV, (with a specified angle if required).

[Dustbak]

Lenses with a short focal length tend to have a wide FoV, and used from the same distance as a longer focal length, will tend to produce a greater perspective than the longer lens, as a result of their wider FoV.

This is incorrect. From the same distance/position a wider lens will have a wider FoV but will have the same perspective as a longer lens.

[Slough]

This is incorrect. From the same distance/position a wider lens will have a wider FoV but will have the same perspective as a longer lens.

That is my understanding too. Perspective is a function of distance only. A wide lens allows you to get closer for a given subject framing and hence increase perspective.

[Dick Roadnight]

From the same distance/position a wider lens will have a wider FoV but will have the same perspective as a longer lens.

Perspective = viewpoint... same viewpoint, same (viewpoint) perspective.

Zero = infinity!

You can achieve zero perspective by shooting from infinity...

You can achieve near-zero perspective by shooting from a viewpoint where the subject distance is very great compared to the format size... i.e. by using a small Field Of View. (The moon seems to have little perspective, viewed from the UK.)

...or you can create a virtual view point at infinity by changing your actual viewpoint for every column of pixels (or pan-and-stitch shot). Mount a Seitz scan back sensor on a rail or lazar beam so that, for every row of pixels, the light reaching the sensor travels perpendicularly to the (near co-planar) subject surface (and the sensor), and you can achieve zero perspective. (I do not think they have invented the kit for this yet, but they have invented a lazar-guided system for painting white lines on football fields, and this system could be adapted)

Co-planar (flat) subjects (like a painting) are perspective-free, anyway, if your sensor is parallel to the subject... but, with a view camera you can achieve this with the camera offset, e.g. to avoid obstacles or to avoid seeing the reflection of the camera in glass.

[cmi]

Well, the OP mentions two distinct subjects: DoF and perspective.  DoF was not contested, but mixing perspective with FoV or framing is pretty regular.

I have not participated in the predecessor of this thread, but I think the underlying issue is, that some MFDB owners feel (IMO unnecessarily) to have to justify their decisions and spendings by a mystic quality of MFDB shots, namely the "3-D look". This quality is often mentioned but it has never been explained yet. I guess the "differerent perspective" of the very wide angle of view with large formats is supposed to substantiate the "3-D look".

In fact, the look of an image with wide ange is very different from others due to the different perspective, but the perspective difference is not caused by the lens itself but by the different position of the camera.

Sorry Christian, couldn't resist.    Being serious is something I am simply not capable of in the world we live in... or is it solemn that I cannot be? http://www.ted.com/index.php/talks/paula_s...ts_serious.html

Cheers,
Bernard

Gabor, Bernard,

(Bernarnd the video is actually a very brilliant one and yes I understand you I too cannot be completely serious in this world, far from it, and your remark gave me a good chuckle  However in such heated (??) discussions I almost never joke just to prevent misunderstandings.)

(Gabor the 3D look is for me how defined pixels are. Of course that cannot be real 3d but I think one can be just more inspired by looking at sharper samples out of cam and call this 3d look instead of the a bit more mushy stuff out of 35mm. 3d look is in my eyes a way of putting: mfdb source images are just sharper. It also mirrors the joy and fascination of owning such a high-end device. Not wanting to start THIS discussion, just mentioning my way to understand the term because I think the term is absolutely valid in this regard in my eyes. I also personally would 3d look being a misconception not rub under the nose of people it gives only heat.)

I now feel my question what this thread is about wich was intended to somehow "sort" the discussion isnt worth the hassle. I re-read portions of this and the last closed thread. My observation: All questions have been answered, there is a lot of knowledge but unfortunately also a lot of misunderstandings.

My conclusion is, it is perfectly possible to achieve with a lower camera through stitching exactly the same results as a higher quality system regarding
   a: pixel sharness: Because oversampling through stitching and downrezzing compensates lower quality look of 35mm
   b: perspective: Because perspective has to do only with my own position in space.

There are of course up- and downsides to mfdb and 35mm. At the end it all depends on what one wants to do and there is no single ideal way. This is boringly common, but in my eyes very important. These discussions degenerate because we fail to see the different perspective of others and that indeed also someone can be happy with a solution wich would not be mine at all. And sometimes if I see I cannot convice the other of my view I just leave him alone. Saves my nerves.

Cheers,

Christian