Talk:Scheimpflug principle

From Wikipedia, the free encyclopedia

I think this page could use images to illustrate the Scheimpflug rule. I'm new to wikipedia so maybe someone else could figure out how they are added?

Thanks! C

Contents

[edit] Scheimpflug

[edit] Refinement/addition to the Scheimpflug principle

This mat'l is rather arcane to add directly, but whoever edits it into shape needs to understand....

The image created by a lens is inverted vertically, horizontally, and also in distance from the lens -- depth. We recognize the 2-D inversion, which is directly proportional - objects near the centerline of the subject remain near the centerline of the image; objects in the far lower right corner (for ex.) of the subject field, appear in the far upper left corner of the image.

In the third, depth dimension the equation for the position of the focus is a bit more complex (it can never be closer to the lens than 1 focal length), but nearby objects in the subject focus distantly from the lens in the image, and objects far from the lens focus near 1 focal length away in the image - as close as it can get. There are equations for that, and they work well.

The Scheimpflug principle recognizes that the focal point of an object (say a small object) follows that equation, regardless of other objects in the view. So the locus (math term) of points where the surface of a horizontal roadway comes to a focus will fall on a plane that satisfies the requirement that all three planes, subject, lens center, and focal plane meet at a common point.

The figure with the Wiki posting illustrates this well. Plus, you don't need all the math and lens principles to 'get it,' and use it.

The term 'depth of field' can be taken to apply at any given point on the image plane, and I think it should be used that way. The image of a small object, viewed in 3 dimensions, forms a cone that comes to a point at the point of focus. [insert sketch here.] We calculate the depth of field as being the distance from the focal point, in the direction toward and away from the lens, at which the cone becomes a certain diameter - a certain amount out of focus, if you will. How much out of focus is a matter of convention, based on the historical capability of film and lenses. Remember:

You don't know what fuzzy is until you've seen sharp.

If you blow up a photographic image by 20X or more, you will discover that what used to appear as 'in focus' really isn't so sharp. The 'exactly in focus' points remain sharp, but the 'might as well be in-focus' points now appear less acceptable than before. With modern high end digital cameras and lenses, you can see this effect on your very own display. What you have done is reduce the allowable diameter of the cone that you call in-focus. You have reduced the depth of field.

Take a photograph of a brick wall at an angle to the wall so that only one vertical line is in focus, and as you blow it up, less and less of it will pass your 'in-focus' criterion.

When the Scheimpflug principle is used to adjust the film and lens planes and get more of the flat road into focus on the film, the depth of field, measured at each point on the image, remains the same - it is controlled by the lens aperture (in f/ stops), the focal length, and the distance of the subject. If you use a wide open lens at say f/4 (that's going to be a large view camera lens!) and adjust to get the horizontal roadway into focus, you will see that a person standing in the road has their feet in focus, but their head may be out of focus. If they are reasonably close to the camera, a smaller f/ stop will be needed to get both the road and the person's head into focus at once, and no amount of Scheimpflug adjustment will get away from that.

The Scheimpflug principle allows you to match the focal plane with the subject, in certain cases. It allows you to make a focal plane that is not parallel to the plane of the lens. It does not change the depth of field calculations, or the depth of the field of the image.

JayWarner 17:56, 16 February 2007 (UTC) Jay Warner Wisconsin, USA quality@a2q.com

Jay is exactly and entirely correct, although his explanation is a bit wordy.

I fixed this article earlier, and added the needed diagram. I cannot see why the article has now been revised back to the spooky language it now has.

Fil Hunter author "Light - Science & Magic" filhunter@verizon.net

[edit] Edit of 25 April 2007

I've made a first attempt at cleaning things up a bit. A few specific comments:

  • I changed "focus plane" to "plane of focus" for two reasons: 1), the latter gets roughly twice as many hits on a Google search, and 2), more important, it seems less likely to be confused with "focal plane" (which apparently was the case with the previous link).
  • I revised the description of the macro photograph, because it doesn't employ the Scheimpflug principle.
  • I eliminated mention of claims that the Scheimpflug principle creates infinite DoF, because it didn't seem relevant—focus and DoF are separate issues. If someone insists on restoring this comment, a link to at least one source would be helpful (I'll quickly concede, of course, that I don't have a verifiable source for "anti-Scheimpflug").
  • I retained the wording "oblique tangent", with some reservations (I understand "oblique" and "tangent", but quite honestly, I still don't quite understand "oblique tangent" ...)
  • I retitled "References" to "External links" because none of the links technically meets WP criteria for verifiable sources. I think removing these links would be a great mistake, however, because I'm not sure there are any sources that would strictly qualify. Moreover, though self-published, Merklinger has been widely cited and discussed, and his diagrams remain the best available. Wheeler includes fairly complete derivations, so the reader can verify his results for herself. The "Tilt and Shift" link also includes considerable useful information, such as a clear demonstration that increasing tilt decreases angular DoF.
  • I don't think WP is the best place to be creating new terms, but in the case of the axis about which the PoF rotates, there may be no choice, as there simply is no standard term. "Counter axis" seems unintuitive, "hinge line" seems a bit informal, and planes intersect at lines, so "pivot point" doesn't seem quite right, either. Things generally rotate about axes, so "rotation axis" or "PoF rotation axis" seem the most descriptive, if not especially elegant. "Pivot axis" might be another possibility.

I think diagrams of the PoF rotation and the wedge-shaped DoF would be helpful; I have both, but they need some minor reformatting. They won't quite match the current diagram, but a slight hodgepodge may be preferable to nothing. An image similar to the text closeup, but with the PoF coincident with the paper would also seem useful; I have a round tuit here somewhere that I just need to get ... JeffConrad 09:27, 25 April 2007 (UTC)

I've removed the cleanup tag. The editor (Vanderdecken) who added the tag gave no specifics, but the edits of 25–26 April 2007 made substantial changes, and there has been no subsequent comment, so I'll assume that most of the concerns have been addressed. This hardly is to suggest that the article would not benefit from additional work. JeffConrad 22:25, 13 May 2007 (UTC)

[edit] Change to Depth of Field section

I changed the phrase "smaller lens f-number" to "larger lens aperture," because, as a photographer, I feel this phrasing better conveys the idea that the wedge-shaped DoF allows a photographer to create photographs that utilize a greater DoF than would be available using parallel planes of focus (ie, with cameras that do not allow movement of the lens and image planes). Though it is purely a semantic difference (a smaller f-number = a larger aperture), I, myself, tend to think in terms of aperture size; thus, for increased DoF, I would think to use a "smaller aperture," rather than "larger f-number." —Preceding unsigned comment added by 71.38.145.27 (talk) 18:37, 21 February 2008 (UTC)

[edit] Phonetics

Can we get a pronounciation guide on this article for "Scheimpflug"? 82.10.108.49 (talk) 22:00, 10 April 2008 (UTC)

[edit] Lensbaby

I've cleaned up the description of the Lensbaby SLR lens, but wonder if its mention here is appropriate. Although the Lensbaby has become fairly popular for creative selective focus, the effect it achieves is only marginally related to the Scheimpflug principle discussed in this article. It seems particularly strange to give it almost as much space as is given to view camera movements and tilt/shift lenses combined; however, I think mention in this context without some qualification would be very misleading. JeffConrad (talk) 21:25, 14 April 2008 (UTC)

[edit] Diagram description

The text doesn't explain what the "Lens object focal plane" in the diagram represents, nor does it mark "J" or theta from the equation on the diagram. It would be helpful if the equation and the diagram used the same symbols.

RobertSeber (talk) 16:04, 9 June 2008 (UTC)

What sort of explanation of "lens object focal plane" are you looking for? The linked article gives a reasonable description, though perhaps it doesn't address your question.
RobertSeber (talk) 06:37, 10 June 2008 (UTC) It seems to be a line floating in space. I understand what the "lens plane" is (a line through the lens), but not what the "lens object focal plane" is.
Any definition I would give would be essentially the same as that in the linked article focal plane. Is the confusion between "object focal plane" and "front focal plane"? JeffConrad (talk) 07:28, 10 June 2008 (UTC)
Yes, that's my confusion. RobertSeber (talk) 07:59, 10 June 2008 (UTC)
The diagram and the article do use the same terminology; the diagram is just missing a couple of symbols :-). It's easier to add an equation and a sentence than it is to update a diagram, but having the symbols on the diagram seems reasonable, so I'll try to get them added. JeffConrad (talk) 22:21, 9 June 2008 (UTC)