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The visible parts of an object, and it's parts with relation to each other, change as it moves through our visual field.

Consider a plus sign + floating in front of a minus sign -.

If you were directly in front of that, you'd see + directly in front of you (as it would hide the -).

If you moved to the left, you'd see -+ to your right, And if you moved to the right, you'd see +- to your left.

If you take a photo and crop it, not preserving the center, you can create an image that cannot be experienced.

e.g. a -+ directly in front of you, or a + to the left.

For this reason, I personally feel that cropping which fails to preserve the center of a photo is a "sin" of cropping.

Does this sin have a name, and does the practice of avoiding it have a name?

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    "If you take a photo and crop it, not preserving the center, you can create an image that cannot be experienced." Huh? Our brains do this all of the time with the signals they receive from our eyes. So yes, an off center crop is a view that certainly can be "experienced."
    – Michael C
    Jan 24, 2017 at 3:14
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    All one has to do to see the + with the - still hidden behind it but not in the center of one's field of vision is to turn at an angle so that the + is not in the center of view and then move right or left until the + covers the - at a point other than directly in front of you.
    – Michael C
    Jan 24, 2017 at 3:18
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    Imagine looking through the viewfinder with your subjects centered. Now, hold a piece of paper between lens and subjects, so that it obstructs the left third of your view. This is exactly the same as cropping the left third of the photo.
    – ths
    Jan 24, 2017 at 21:31
  • @ths no it's not because the subject still falls on the same area of the film.
    – z5h
    Jan 25, 2017 at 13:25

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I do not know if it has a name, but this is essentially what tilt-shift lenses and view cameras can do in terms of lens shift. Only instead of cropping, you move the lens and thereby the image circle in relation to the film or sensor. This also leads into the second part of your question, in that it can sometimes be very useful (for instance, to avoid leaning buildings) and should not always be avoided.

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  • Indeed, I frequently find myself committing this sin to avoid the sin of not holding the camera level for building shots, not having a real tilt-shift lens.
    – junkyardsparkle
    Jan 24, 2017 at 0:29
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The phenomenon you describe is called parallax. Foreground objects appear to shift in their relationship to background objects due to a change in the location of the viewpoint. The magnitude and direction of the apparent shift is intertwined with the ratio of the distance between foreground and background objects and the magnitude of the shift

Parallax allows people with normal vision to view the world in 3D. This sensation grants us depth perception. Those with only one functioning eye lack our marvelous three dimensional vision. Without 3D vision, judging distances is challenging.

When we image with a standard camera, the image we capture a one-viewpoint view. When we present this image for viewing, we can enlarge, reduce or crop. Such action will not induce a parallax shift. 3D images are possible. Specialized cameras take two or more pictures from different viewpoints either simultaneously or serially. These multiple viewpoint images when properly presented allow 3D photography. Holography is a technique that displays a 3D image by capturing an image of the wave front of light radiating from a vista using lasers and mirrors.

It is bizarre that you should call a parallax view a “sin”. I view the parallax view as a blessing.

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If you take a photo and crop it, not preserving the center, you can create an image that cannot be experienced.

Say what?!?!?

All one has to do to see the "+" with the "-" still hidden behind it but not in the center of one's field of vision is to turn at an angle so that the "+" is not in the center of view and then move right or left until the "+" covers the "-" at a point other than directly in front of you.

diagram

As the above diagram makes obvious, one can align the "+" and "-" signs so that the "-" sign is not visible without the "+" sign being centered in the middle of the frame. By rotating the camera about 30° to the right being careful to center the rotation on the optical center of the lens, often incorrectly called the nodal point, one could make the red "+" sign occupy the same position the green one is occupying when the camera is pointed directly at the red one.

Only when the rotation is not centered on the optical center of the lens would we experience parallax that would make the "-" visible beside the "+". But we could easily correct that by moving right to left along a line parallel to plane occupied by the "+" sign.

If one were to shoot the red "+" with a wider angle of view and crop the image as shown it would appear the same as the uncropped photo of the green "+". The result of cropping a photo of the red "+" off center is most certainly an image that can "be experienced" without cropping as is demonstrated by the photo of the green "+".

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  • Thanks but you're wrong. In your image the green symbols and camera are lined up. As are the red symbols and camera. If 3 things are lined up, and one object moves, they are no longer in a straight line. Simple geometry.
    – z5h
    Jan 24, 2017 at 15:49
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    @z5h you misunderstand Michael's point. Cropping off-center does not create motion in the scene. And Michael wasn't talking about translational movement out of line. He was talking about rotational movement of the point-of-view of the camera. If the camera is rotated about the optical centers of the lens (also called the no-parallax-point), then no parallax shift occurs because everything is still lined up.
    – scottbb ♦
    Jan 25, 2017 at 2:20
  • @z5h A camera can be rotated around the optical center of the lens without any movement in the perspective of the camera. A human with stereoscopic vision can not, but a camera with monocular vision can. In the case of us humans, though, our brains are constantly selectively interpreting the signals from both eyes and can effectively do the same thing without any movement of the eyes at all.
    – Michael C
    Jan 25, 2017 at 3:21

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