WHAT IS THE SCHEIMPFLUG RULE?
WHAT IS THE SCHEIMPFLUG RULE?
These will do a better job of explaining it than I can:
http://www.trenholm.org/hmmerk/HMbooks3.html http://home.fox.nstn.ca/~hmmerk/VuCamTxt.pdf http://home.fox.nstn.ca/~hmmerk/HMArtls.html http://people.westminstercollege.edu/faculty/ccline/photos/itlf/largef ormat1.html
In a hand camera (one in which the relationship of film plane and lens plane is fixed and parallel) in order to achieve a condition in which everything in view is in focus, one must rely on depth of field entirely.
View cameras on the other hand permit adjustment of the lens plane and film plane which allows one to employ the Scheimpflug rule to bring near and far objects into focus, relying less on depth of field to do the job.
Imagine if you will a scene in which the subject lies predominantly on a plane that is parallel to the ground. Perhaps some railroad tracks make a good example. Now when setting up the camera, the lens plane (a plane that is perpendicular to the optical axis of the lens) is mostly vertical and if extended using one's imagination, eventually touches the ground, which in this case is the subject plane. With the camera in its neutral condition (no adjustments made thus far) tilt the back (film plane) rearward at the top until it is as such an angle that the imaginary continuance of that plane intersects the line at which the lens plane and subject plane meet. You have now established a Scheimpflug relationship that will render everything lying on the subject plane in perfect focus regardless of it being near the camera or off in the distance.
This is an extremely important and handy technique, but is fraught with traps if not understood thoroughly. Some reading and experimentation is in order if you want to use this to fullest advantage. But, at least you now have some idea of what it is and what is does.
Hope that helps.
Obviously you haven't done a search on this forum. perhaps you should.
The Schiempflug Theorem is very simple: when the plane of the subject (as determined by the photographer) , the film plane and the plane of a lens' nodal point that is perpendicular to the lens axis all intersect in a line, all points in the subject plane will be in focus regardless of the aperture .
To understand this you need to know some very basic Euclidean geometry: A plane is defined by any three points and a line is defined by two points.
Like Ellis said...
The image plane of sharpest focus passes through the line in which the film plane and lens plane intersect.
The only problem is that, on some lenses, it is not obvious where the lens plane is. On most LF lenses it somewhere near the lens board or shutter.
This does work: pick a line on the floor and point the lens plane and the film plane at it, and the floor will be in focus.
Is it the focal length of he lens from the film plane when focused at infinity?
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The best visual demonstration to the Scheimpflug rule is in
Merklinger's Magazine Articles 91-97
Choose the various viewcam quick time 'movies' to see it at work along with another rule which although not as well known is equally important, the Hinge Rule. The geometries involved are somewhat complex and need a little time to study and remember. There is nothing that can be done about the complexity, after all, no one invented the laws of physics. However you will get a basic understanding of what happens as you move parts of the camera in a graphic way that no one has explained better than Merkingler. While there move the slider back and forth until you get the thing down pat. Also you may look at other related issues which Merklinger does an outstanding job of explaining. Good luck!
Scheimplug's rule is easily derived from basic laws of geometrical optics withut maths.
See my article on Tuan Luong's web site :
To go further mixing Depth-of-field and Scheimplflug's rule, I've tried ina comp anion article to find something as simple as possible almost without maths
an updated version in French including an explanation of a diagram by Strobel in his book is here, and the updated English version will be posted on Tuan Luong's web site some day (Tuan is a volunteer and deserv es a medal for the excellent work he does for large format enthusiasts)