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Author Topic: DoF and Perspective Revisited  (Read 14010 times)
cmi
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« Reply #100 on: September 08, 2009, 07:58:33 PM »
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Quote from: Ray
...

As a theoretical construct and property of lenses, unrelated to the making of a picture or composition and therfore excluding the perspective of a potential viewer, the theroetical perspective through the lens is independent of its focal length or the format of the camera it is attached to, and is determined only by the distance between the lens and the theoretical subject.

However, when creating a photographic composition, which most photographers try to do now and again, the focal length of the lens and the format size of the camera will both influence the distance to the subject(s), the size of the subject within the composition and the number of individual subjects or objects within the composition at varying distances from the photographer.


...

Ok, written a bit complicated, but I translate this basically to:

===

In theory, perspective is independent of focal lenght.

But as soon as someone says "a tele optic compresses and a wide optic exaggerates perspective" wich everybody does, the meaning of perspective becomes different and now involves also the field of view of a lens. (As addition to only the position.)


===

IF we where to insist on using **only** the correct definition of perspective, we could rephrase it as:

To achieve roughly the same framing for a wide and a tele optic, one has to move the tele optic farther away because of its narrower angle of view. As a result the perspective changes. The same view wich occupied a big angle of view from near disctance now occupies a small angle of view and due to this the also perspective differs.

The common speech has shortened this, dont mention the movement because it is implicit (you always have to do it) and instead just takes the focal lenght (wich in play with the sensor size results in a angle of view) as a synonym for the impression that will result, and calls this perspective.

So essentially the abbreviation "a tele optic compresses and a wide optic exaggerates perspective" centers about the practial consequences and dont care about the correct definition. One half is the scientifically correct definition, the other half is the practical consequence. Both can't be neglected. Both are valid in their context, else they wouldnt exist.
« Last Edit: September 08, 2009, 08:26:46 PM by Christian Miersch » Logged
cmi
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« Reply #101 on: September 08, 2009, 08:03:46 PM »
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Quote from: Ray
Christian,
Regardless of whether a wide-angle lens produces a nice perspective or a horrible perspective, it produces a different image to that produced by a longer lens (from the same position) and the objects in that different image will relate in a way which produces a changed perspective of the viewer, will they not?

Ray, I now see this answer of yours after I have written my other posting just above this one. I would essentially write a similar explanation here so please take my other (first) answer also as an answer to this. (Basically I would agree partly that for practial purposes the images ARE different, but the perspective... oh well, and there I am at my last post  )

Cheers,

Christian
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Ray
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« Reply #102 on: September 08, 2009, 08:35:42 PM »
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Quote from: Christian Miersch
To achieve roughly the same framing for a wide and a tele optic, one has to move the tele optic farther away because of its narrower angle of view. As a result the perspective changes. The same view wich occupied a big angle of view from near distance now occupies a small angle of view and due to this the also perspective differs.

Agreed! But I get the impression there's something else happening with ultra-wide-angle shots which are wider than the normal FoV of human vision. The wide-angle photographic image allows the eye and brain to capture in one glance, perspective detail which in the real world would be impossible. Whilst the FoV of the human eye is quite wide, if one includes periphery vision which is good for detecting movement but hopleless for discerning detail, the actual FoV of focussed human vision is quite narrow. I never get a sense in the real world, when examining detail from a close distance, of the apparent perspective distortion one finds in a wide-angle photographic image.
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Murray Fredericks
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« Reply #103 on: September 08, 2009, 08:48:15 PM »
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Quote from: Ray
Agreed! But I get the impression there's something else happening with ultra-wide-angle shots which are wider than the normal FoV of human vision. The wide-angle photographic image allows the eye and brain to capture in one glance, perspective detail which in the real world would be impossible. Whilst the FoV of the human eye is quite wide, if one includes periphery vision which is good for detecting movement but hopleless for discerning detail, the actual FoV of focussed human vision is quite narrow. I never get a sense in the real world, when examining detail from a close distance, of the apparent perspective distortion one finds in a wide-angle photographic image.


All this can still be explained by the basic priciples of optics and physics...

your eye is a lens too...
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Ray
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« Reply #104 on: September 08, 2009, 09:55:22 PM »
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Quote from: Murray Fredericks
All this can still be explained by the basic priciples of optics and physics...

your eye is a lens too...

But the brain has to interpret everything that is seen. I don't believe for example, when you stand one foot away from a person, that his/her features appear as distorted as they would in a wide-angle photo taken from the same distance. I mean, if you are standing close to someone in a lift for example, you don't exclaim (or even think), "Oh! You do look funny!" However, if you were to take a photo of that person from the same distance, using say a 14mm lens on a DSLR, the photo could be quite amusing.

Is this effect explained by optics or by the way the brain interprets the unusual perspective in a image provided by the additional objects that only a wide-angle lens can capture?
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Jack Flesher
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« Reply #105 on: September 08, 2009, 10:14:33 PM »
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Quote from: BernardLanguillier
OK, fair comment. I assume that you used C1 Pro to convert both these files? Did you do side to side comparisons?

If it is the case, that might save me 800 US$ if these were available.

Thanks.

Cheers,
Bernard

C1 pro yes, as it is my preferred converter.   Side-by-sides not exactly.  Similar shots in similar conditions, not scientifically controlled but literally thousands of frames -- more than enough that I am certain .   I'll share this little verbal example with you though: When we had our workshop in Moab this past winter, myself and two assistants were shooting a late landscape with the sun setting behind us.  Here the sky was still light but the foreground was dark in shadow, just the tips of the mittens still lit.  One assistant and myself were shooting our MF outfits (P45+) and the other assistant was shooting his 5D2.  We -- the P45= shooters -- were shooting single frames as we had all week, easily capturing the entire range of tonality.  However, the 5D2 shooter was now shooting doubles so he could HDR blend -- his comment as close as I can remember it was, "I have to shoot two because I can't get the full range from a single out of my Canon."

Best,

 
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Jack Flesher
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« Reply #106 on: September 08, 2009, 10:19:08 PM »
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Totally OT PS: I've discovered a problem with the ignore feature -- if somebody you have not put on your ignore list quotes somebody you have, you can see the quoted post.  Not horrible, but like watching a train wreck you just cannot help yourself and in this case, I read the totality of nonsense  I specifically tried to avoid...

/rant
« Last Edit: September 08, 2009, 10:19:48 PM by Jack Flesher » Logged

Dick Roadnight
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« Reply #107 on: September 09, 2009, 04:12:38 AM »
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Quote from: Jack Flesher
Totally OT PS: I've discovered a problem with the ignore feature -- if somebody you have not put on your ignore list quotes somebody you have, you can see the quoted post.  Not horrible, but like watching a train wreck you just cannot help yourself and in this case, I read the totality of nonsense  I specifically tried to avoid...

/rant
Yes, Jack... I get the same problem, but I ignore any post which quote the member I ignore.

It would be nice if other members (who normally make constructive posts) did not respond to, or quote, the member(s) we ignore!
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cmi
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« Reply #108 on: September 09, 2009, 05:34:43 AM »
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Quote from: Ray
...I never get a sense in the real world ... of the apparent perspective distortion one finds in a wide-angle photographic image.

Quote from: Ray
...Is this effect explained by optics or by the way the brain interprets ... ?

Ray,

I wrote an answer but I feel thats a sudden shift (our perception / limits of 2d reproduction). Hopping from topic to topic, not my cup of tea...


Christian
« Last Edit: September 09, 2009, 10:09:35 AM by Christian Miersch » Logged
Jack Flesher
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« Reply #109 on: September 09, 2009, 12:00:33 PM »
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Quote from: Dick Roadnight
It would be nice if other members (who normally make constructive posts) did not respond to, or quote, the member(s) we ignore!

For sure it would... But just like watching that train wreck, sometimes those comments are just so far out there and off base that it is difficult to let them go without comment. Problem is, some folks just refuse to accept they're wrong regardless of how absurd their position is
« Last Edit: September 09, 2009, 12:01:33 PM by Jack Flesher » Logged

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