Scheimpflug's rule
max. Sharpness in optical imaging when the
image , lens and object plane / plane of focus intersect in a common straight line
The Scheimpflug principle or Scheimpflug condition states that for an optimally sharp optical image to object , lens - and image plane must intersect in a common straight or intersect when the focus should be greatest. These statements are named after the Austrian officer and cartographer Theodor Scheimpflug . Further designations are cut line condition , sharpness expansion according to Scheimpflug or expansion of the depth of field (according to Scheimpflug) .
Borderline parallelism
In a common, simple camera, the image plane (film or image sensor) and the lens plane are parallel to one another. Consequently, the sharply imaged object plane, also called the plane of focus, lies parallel to both. The common line of intersection can be imagined at an infinite distance. If a (flat) object is now photographed that is inclined to the plane of focus, this object is only shown completely in focus in the area of the intersection of the plane of focus and the plane of the object.
Illustration of inclined planes
If an inclined object plane is to be imaged in focus, the objective and image planes must be inclined towards one another in accordance with the Scheimpflug condition so that they intersect and their line of intersection falls into the object plane or plane of focus to be sharply imaged.
tilt : can be swiveled vertically against the camera (curved scale)
shift : can be pushed vertically against the camera (2 knurled screws)
In older photo technology , this was only possible with large format cameras with bellows . In such cameras i. d. R. the lens (or its holder, the lens standard ) i. d. Usually pivoted about a horizontal axis. Special lenses for miniature photography have panning (Engl. Tilt ) integrated into the lens housing. Tilt the lens backwards. the front of a tall building is brought into focus, and it is shown in sharp focus from top to bottom despite the different distances between its parts.
Scheimplug's rule is therefore used with advantage u. a. often noted in architectural photography and historical building photography. Because large format images with high sharpness are required there, the recording format must already be large. In the case of the larger focal length lenses to be used , the depth of field is relatively small, the negative effect of which on image sharpness is mitigated by observing the Scheimpflug condition.
Story and explanation
Scheimpflug took aerial photographs with the help of kites , balloons and airships in order to produce maps, whereby oblique photographs were also taken.
These were made in order to be able to get by with as few flights as possible. Their number could be reduced to a third if the two stripes adjacent to the trajectory were also photographed. Since the object distance was approaching infinity, these recordings with standard cameras (parallelism between the three planes) were sufficiently sharp, they were merely distorted.
When it came to rectifying the aerial photos, he discovered the rule named after him by setting his rectifying device (a type of enlarger) accordingly so that the sharpness contained in the picture was not lost. The Scheimpflug rule was originally applied to the post-processing of photographs and only afterwards became common property of photo technology when taking photos with adjustable large format cameras with bellows and with the later tilt and shift lenses for 35 mm cameras.
The theory of the Scheimpflug rule was already known in 1855, but its importance for photogrammetry was largely recognized by Theodor Scheimpflug and described in one of his patents.
The Scheimpflug rule is a special statement contained in the lens equation in general.
This equation is very often only dealt with for the special case of the three mutually parallel planes, whereby the complete relationship between the object and image plane, including the objects or images of any shape contained in them, can be found by mapping a single point. They are true-to-scale images with one another, so that their mutual relationship can only be represented using the image scale .
The lens equation is generally to be used for the representation of the Scheimpflug rule. What is sought is the position of the image plane in which objects are sharply imaged in an object plane that assumes any position relative to the lens axis or plane. The object and the image are mutually distorted, and there is no image scale for the image (there is only one image scale for the small point environments and a different image scale for each point).
The result of the investigation, which cannot be briefly presented, is:
An object plane that is not at right angles to the lens plane (objective plane) is imaged as an image plane that is also not at right angles to that plane. The object and image planes intersect with the lens plane in one and the same straight line.
Application of the rule to lenses with two main planes
An objective usually consists of several lenses and therefore not only has a lens plane like a thin lens but a main plane on the object side and a main plane on the image side . Scheimpflug's rule reads more precisely that the focal plane intersects with the main plane on the object side at the same distance from the axis of the lens as the image plane intersects with the main plane on the image side, and that both lines of intersection are parallel to one another. Both lines of intersection are on the same side of the optical axis.
"Double" Scheimpflug
Some publications call the possible tilting around two axes the double Scheimpflug in contrast to the simple Scheimpflug , in which the plane of focus is tilted only around the horizontal or the vertical axis. Geometrically, the double Scheimpflug is a simple tilting around an inclined axis. The Scheimpflug rule makes no statement about the direction of the intersection line between the three planes and therefore also includes the double Scheimpflug . In practice, the “simple” Scheimpflug setting “staggers” (tilts) when the base tube of the camera is not set horizontally if it does not have a central pivot point (usually under the base tube). The stagger-free double Scheimpflug, the optically correct focus setting, is only possible using a central pivot point.
Web links
Remarks
- ↑ a b Architectural photography is mostly about depicting the fronts of high buildings without distortion, ie avoiding falling lines . The Scheimpflug condition does not play a role in this application, because the three levels remain parallel to one another. The lens is shifted or shifted transversely .
- ↑ Just as an object can be depicted in a distorted manner with any standard camera, the image can also be rectified with any standard enlarger. Photo amateurs have always made use of this option by inclining the picture cassette accordingly. Since the Scheimpflug condition is not fulfilled, one makes do with stopping down strongly during the exposure in order to obtain sufficiently sharp enlargements.
Individual evidence
- ^ A b Josef Krames: Festschrift on the 150th anniversary of the state surveying system in Austria. Transformation and rectification of photographic recordings according to Theodor Scheimpflug. 1956, accessed February 2, 2020 .
- ↑ Sharp elongation according to Scheimpflug
- ↑ Eriwalt Dietz Laursonn: Handbook of photo technology . Ed .: Gerhard Teicher. 6th edition. VEB Fotokinoverlag, Leipzig 1974, DNB 750176121 , large picture photography 2.2 Extension of the depth of field, p. 436 ff .
- ↑ Scheimpflug and the use of the Tilt Shift •
- ^ Josef Krames: Festschrift for the 150th anniversary of the state surveying system in Austria. Scheimpflug's land survey from the air. 1956, accessed February 2, 2020 .
- ^ Roger Rossing: Handbook of Photo Technology . Ed .: Gerhard Teicher. 6th edition. VEB Fotokinoverlag, Leipzig 1974, DNB 750176121 , laboratory technology 1.2.2 Distortion, p. 356 .
- ↑ a b No. 751347: Method of Distorting Plane Image by Means of Lenses or Mirrors. (pdf) United States Patent and Trademark Office , February 2, 1904, accessed February 16, 2020 .
- ^ Siegfried Wetzel: Geometric optics, optical imaging and Scheimpflug rule
- ↑ Harold M. Merklinger: FOCUSING the VIEW CAMERA