DE10358374A1 - Electronic camera objective for e.g. machine-vision imaging, having greater depth of focus at f numbers exceeding specified value, combines condenser lens with correction lens - Google Patents

Abstract

Between diaphragm (1) and image plane, two optical components are included. One is a condenser lens dominating refraction (2). The other lens (3) provides correction, reducing distortion and image field curvature. An independent claim is included for the corresponding imaging method.

Description

The The invention relates to a lens for images with a large depth of field.

The Invention is preferably for Illustrations can be used with electronic cameras.

in the State of the art are lenses with variable aperture, in which the necessary depth of field is achieved by dimming, known. The dimming corresponds an enlargement of the F-number k. Size depth of field be for k> 5.6. Because lenses with variable aperture designed for maximum aperture are, need the optics schemes at least five Lenses. Such lenses are complex and expensive.

The Conditions for the achievement of a given depth of field with digital imagers is in [N. Schuster: Proc. SPIE 5249 (2003)]. At f-numbers k> 5.6 are simpler the optical schemes compared to lenses with smaller f-numbers. For machine vision applications are both polychromatic and monochrome illuminations of practical interest.

Of the Invention is based on the object, an objective of the above specify the type for which suitable for use in electronic cameras, a large depth of field possible with a minimum number of refractive surfaces and inexpensive to produce is.

According to the invention Object with a lens, which specified in claim 1 Has features solved.

advantageous Embodiments are specified in the subclaims.

The Lens consists of an optical system with a f-number k> 5.6 to achieve a huge depth of field with at least one collecting component dominating the refractive power between opening panel and image plane and at least one correction element, the distortion and field curvature improved, with additional Correction elements (eg for the correction of chromatic aberrations) are added can.

The Correction element preferably consists of a diverging lens and / or an aspherical Deformation of a refractive surface.

• 1. Das Objektiv kommt mit einer minimalen Anzahl von optischen Elementen, insbesondere Linsen, und mit einer Festblende aus.
• 2. Das Objektiv ermöglicht eine auf den digitalen Empfänger abgestimmte Bildqualität.
• 3. Alle Ausführungsformen sind im monochromen Licht einsetzbar.
• 4. Mit einfachen Mitteln kann eine auch im polychromen Licht einsetzbare Ausführung geschaffen werden.

The invention is characterized by a number of advantages. These include in particular:

• 1. The lens comes with a minimum number of optical elements, in particular lenses, and with a fixed aperture.
• 2. The lens allows image quality tuned to the digital receiver.
• 3. All embodiments can be used in monochrome light.
• 4. With simple means an applicable even in polychromatic light design can be created.

The Invention will be explained in more detail below with reference to an embodiment.

In the associated Show drawing:

1 an optical arrangement with a Smyth field flattening lens as a correction element,

2 an arrangement with a plano concave lens as a correction element,

3 an arrangement with aspherical deformation of the collecting optical element as a correction element
and

4 an arrangement with aspherical deformation of the collecting optical element as a correction element and with additional chromatic radius for correcting the chromatic aberration.

The optical arrangement consists of at least one collecting and refractive power dominating optical element 2 behind the opening 1 is appropriate. By the appropriate choice of the aperture distance, the refractive index, the radii and the thickness of the collecting element 2 an astigmatism corrected image is achieved. The remaining disturbing aberrations image field curvature and distortion are caused by at least one correction element 3 reduced to a harmless level.

At the in 1 The arrangement shown is used as a correction element 3 uses a Smythe field-flattening lens, the curvature of which derives from the Petzval condition. This achieves a flat image field and corrects the distortion well. This arrangement is particularly suitable for images on analog image sensors.

2 shows an embodiment in which as a correction element 3 a plano concave lens is arranged whose position and curvature is determined so that the main beam tilt behind the optical system does not exceed a predetermined maximum value. An optimum between Bildfeldebnung and residual distortion is adjustable. This arrangement is particularly suitable for imaging on digital image sensors with microlens arrays.

Another embodiment explained 3 , This serves as a correction element 3 an aspherical deformation of the vertex of the refractive power determining surface of the collecting optical element 2 , As the field angle increases, the curvature of the convex surface of the collecting optical element increases 2 decreases, also reduces the field curvature compared to the execution according to 2 , At the same time the distortion is corrected and the main ray inclination is kept low. By a suitable choice of the conical constants of the refractive power-determining surface of the collecting optical element 2 and the aperture distance, a minimum circle of confusion is achieved with fully compensated distortion throughout the field of view. This arrangement is particularly suitable for monochrome imaging on digital image sensors with microlens arrays. With this arrangement, large object-side field angles can be realized.

In the 4 arrangement shown has all structural features and thus all the advantages of 3 shown arrangement. In addition, a so-called chromatic radius 4 for correcting the chromatic aberrations in the refractive power determining optical element 2 introduced. This chromatic radius 4 separates optical media with the same main refractive index and different dispersions. Thus, the outstanding properties of the arrangement after 3 also effective for polychromatic light (for example, white light). This arrangement is particularly suitable for color projection onto digital image sensors. With this arrangement also large object-side field angle can be realized.

1

aperture stop

2

sammeldes optical element

3

correction element

4

chromatic radius

Claims (6)

Lens for images with a large depth of field with an optical system with a f-number k> 5.6, characterized in that between aperture ( 1 ) and image plane at least one collecting, the refractive power dominant component ( 2 ) and at least one correction element ( 3 ) are arranged to reduce distortion and field curvature. Method according to claim 1, characterized in that as a correction element ( 3 ) is arranged a diverging lens. Method according to claim 1 or 2, characterized in that as a correction element ( 3 ) an aspherical deformation of the refractive power-determining convex surface of a converging lens ( 2 ) is used. Method according to one of the preceding claims, characterized in that at the component dominating the refractive power (22) and / or at the correction element ( 3 ) are arranged additional correction means for the correction of chromatic errors. Lens according to claim 4, characterized in that to remedy the chromatic errors in the collecting component ( 2 ) a chromatic radius is arranged. Lens according to one of the preceding claims, characterized in that the aperture ( 1 ) facing side of the refractive power-determining element ( 2 ) is curved.