Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
  • G02B27/46—Systems using spatial filters

Definitions

• the present invention relates to a device and a method for focusing in optical equipment. More specifically, the invention relates to a device and a method for internal focusing in a device of so called plenoptical type.
• a scene is reproduced when light from one or several external objects, herein called a scene, is centrally projected in a very small light aperture or is deflected by one or several lenses towards a light receiving surface, or via an eyepiece to the retina of an eye.
• the very small aperture or the system of lenses will in the following be referred to by the general term "lens".
• the light receiving surface consists of a focusing screen, a photographic film or, for instance, a CCD sensor being placed in or near the focal plane of the lens.
• a telescope or a microscope an eyepiece is used, whereby the focal plane of the eyepiece replaces the light receiving surface within the camera.
• the diaphragm By altering the size of an aperture of a diaphragm placed in the optical path the diaphragm typically being a device with an adjustable central aperture, it is also possible to shield the outer areas of the incident beam of light to a desired extent. These outer areas of the incident light beams represent reproduction deviations that create a blurred image of objects being positioned in front of or beyond the selected distance for a sharp reproduction, and it is consequently possible to use the diaphragm to adjust the depth of field in the image.
• a specific type of optical equipment is known as "plenoptical equipment".
• the plenoptical equipment is characterised in that the incident light passing through the lens is divided into several sub-images by a plurality of miniature lens elements or very small apertures, typically disposed in a plate in the optical path beyond the lens.
• the basics of this technology is described in the article "Single Lens Stereo with a Plenoptic Camera", Edward H. Adelson and John Y.A. Wang, IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol 14, No 2, Feb 1992.
• the miniature optical elements are disposed in, or adjacent to, the focal plane of the lens.
• these are so tiny that they generate a mirrored image via a projection centre according to the principle for "camera obscura”.
• miniature lenses are used to create a corresponding image.
• a light sensitive surface typically a CCD sensor, is placed to receive the sub-images at a fixed distance from the miniature optics, and the miniature optics are placed at a fixed distance from the lens.
• optical section corresponding to a section perpendicular to the optical axis i.e. a section parallel with the image surface in the conventional plenoptical equipment as described above, differs to some extent from any other such sections that are perpendicular with respect to the optical axis and that are displaced along the optical axis with respect to the first section.
• This information cannot be registered using conventional plenoptical devices.
• this has the effect that a sharp detailed photographic image at an arbitrary depth cannot be obtained without changing the optical section, i.e. by altering the focus setting of the lens. Furthermore, it is not possible to perform good measurements of depth without altering the optical section.
• the device according to the invention enables simultaneous registering of a visual image and depth information for a subsequent separation of information and/ or three- dimensional visualisation.
• the device according to the invention allows, by way of its movable focusing plate being provided with apertures, that optical sections are made in the image space present beyond a lens. Thereby, an effect corresponding to adjusting the focus of a lens is obtained without needing to disturb the lens, even in a case where the lens has no focusing device.
• the focusing plate is rotatable around the optical axis in order to register minute differences between images obtained on the same section perpendicular to the optical axis, but using different positions for the apertures of the focusing plate.
• Fig. 1 is a schematic perspective view of a focusing plate according to the invention
• Fig. 2 is a front view of a section of a focusing plate according to the invention, showing an embodiment of aperture positions;
• Fig. 3 is a cross-sectional view taken along the line I-I in Fig. 2;
• Fig. 4 is an enlarged cross-sectional view according to Fig. 3;
• Fig. 5 is a schematic view of a device according to the invention being equipped with an eyepiece;
• Fig. 6 is a cross-sectional view taken along the line II-II in Fig. 5
• Fig. 7 is a cross-sectional view, seen from above, taken through the assembly according to Fig. 1 ;
• Fig. 8 is a cross-sectional view, seen from above, showing the intensity of light in the image plane for a first position of the focusing plate
• Fig. 9 is a cross- sectional view, seen from above, showing the intensity of light in the image plane for a second position of the focusing plate
• Fig. 10 is a schematic view of an embodiment comprising fibre optics.
• like components are given like reference numbers.
• a focusing plate 2 is provided with apertures 5 to allow light to pass through the plate.
• the focusing plate 2 is mounted along the optical axis OA of a lens 1 in such a way that the plate is movable along the optical axis with respect to the lens.
• This is schematically illustrated in Fig. 1 by the lens 1 being fixedly mounted to a rod 3 that is parallel to the optical axis OA, and a sleeve 4 having the focusing plate 2 fixedly attached thereto is slidably mounted onto the rod.
• the lens could be a single lens or a lens assembly consisting of several separate lenses.
• other light collecting means such as one or several mirrors could be used instead, or as a complement, to direct light to or from the focusing plate.
• the purpose of the focusing plate is to block a part of the light received via the lens. That part of the light that is not blocked will continue through the apertures of the focusing plate towards an image plane IP.
• image plane refers to a section in the image space where information is registered.
• a light receiving means (not shown in Fig. 1) which is specific for different embodiments is placed in the image plane, such as the focal plane of an eyepiece or the light receiving section of a fibre optical waveguide having a second end for instance ending in the focal plane of an eyepiece.
• the image in the image plane can be observed through the eyepiece or be registered with, for example, a camera.
• Fig. 7 illustrates the image space extending beyond the focal plan LF of the lens, wherein light beams are represented by lines with arrowheads.
• the focusing device 2 allows focusing within this virtual representation, as opposed to focusing using the lens which alters the image space itself.
• the apertures 5 of the focusing plate 2 are formed to any suitable shape.
• the apertures are formed as generally circular through holes in a plate of an opaque material, such as graphite. It is essential that each aperture is not so small that a central projection of the camera obscura type is obtained, or that other not desired phenomena, such as diffraction, occur.
• the dimensions and the overall shape of the focusing plate should be selected to suit the equipment in which the focusing plate is to be used.
• a typical shape is a circular disc having a thickness of about 50-200 ⁇ m.
• the thickness of the focusing plate and the dimensions of the apertures should be correlated to each other in such a way that a generally continuous reproduction is obtained in the image plane.
• FIG. 2 An embodiment of the light transferring apertures of the focusing plate is shown in Figs. 2 to 4.
• the focusing plate 2 is provided with apertures 5, said apertures being formed as through holes in the plate disposed in a generally equalateral triangle pattern, having an edge-to-edge distance of S between an aperture and each of its adjacent apertures.
• each one of the holes extending through the plate with an inlet diameter DI, an outlet diameter DO being larger than the inlet diameter, and intermediate diameter increasing linearly from the inlet diameter to the outlet diameter thereby giving the aperture the shape of a truncated cone.
• Asymmetric-shaped conical holes are also feasible for non-symmetrical light-cones.
• the conicity of an aperture is selected based on the focal length of the lens and the operative interval of the focusing plate along the optical axis, as well as incident light cone conicities, in order to ensure that no part of the walls of the aperture beyond the inlet opening intersects the beam of light.
• the inlet opening of an aperture is selected as large as possible with respect to the light blocking area in order to obtain the brightest possible image, e.g. selecting an inlet opening diameter of 50 ⁇ m.
• the angle ⁇ is the cone angle for a symmetrical cone of light in the image space beyond the lens having its axis coinciding with the optical axis of the lens.
• an embodiment including apertures of hexagonal shape being hexagonally distributed over the focusing plate is preferred for optical reasons.
• the embodiment described above, i.e. including apertures of circular shape that are distributed according to an equalateral triangle pattern, is assessed to be advantageous in that an easily manufactured focusing plate providing an image of generally sufficient quality is obtained.
• the focusing plate is mounted substantially perpendicular to the optical axis OA of the lens (ref. to Fig. 1) via an attaching device being slidable with respect to the lens.
• An embodiment of such an assembly is illustrated in Fig. 5 and 6, wherein a lens 11 is mounted at the end of a tube 17 by means of a threaded attaching sleeve 16.
• a sleeve 18 is inserted into the other end of the tube 17 and is displaceable within the tube according to the telescope principle.
• a gear rack 19 is fixedly attached to the outer surface of the sleeve 18 and is oriented in the axial direction of the sleeve 18.
• the cogs of the gear rack protrude out through a longitudinal opening 20 in the tube 17.
• a feeding means for feeding the tube forward and backward is schematically illustrated in Fig. 5 and 6 with a cog wheel 21 which can be rotated to move the tube 18 into, and out off, the tube 17 along the optical axis OA of the lens.
• An eyepiece 22 is fixed to the outer end of the sleeve 18 with a threaded attaching sleeve 23.
• the sleeve 18 is threaded on its inside and an inner sleeve 24 provided with an external thread is screwed into the sleeve 18.
• the inner sleeve 24 is at one end provided with a flange 25 against which a focusing plate 12 is fixedly attached, for example with an epoxy adhesive or an additional threaded plastic sleeve (not shown) .
• the inner sleeve 24 can be fixed against the outer sleeve 18, e.g. with a locking lacquer.
• the position of the focusing plate 12 is adjusted by rotating the cog wheel 21. Thereby, the reproduction present in the image plane will be focused at different depths in the viewed scene, which is observable via the eyepiece. This effect shall now be described in more detail.
• the position of the focusing plate which is displaceable along the optical axis, is selected along the optical axis in such a way that it is positioned within the image space present beyond the lens, i.e. beyond the focal plane of the lens, as is shown in Fig. 7.
• a three-dimensional virtual representation of the scene to which the lens is directed is present.
• the image plane moves through this virtual representation.
• different sections of the representation are more or less sharply reproduced in the image plane.
• Figs. 8 and 9 is illustrated the measurable light intensity I in the image plane IP from an object 41 of the virtual representation for two different positions of the focusing plate 2 with its apertures 5, one of the positions being shown in Fig. 8 and the other in Fig. 9.
• Light beams are represented by lines with arrowheads, and the light intensity is schematically illustrated with a graph to the right in each figure.
• Figs. 8 and 9 is also illustrated a way in which a variable focusing of the reproduced scene is achieved without the need to focus by the lens.
• focusing can be accomplished also using a lens which in itself entirely lacks any focusing device.
• the viewed scene is obtained in the image plane, wherein the reproduction is built up of sub-images from each aperture in the focusing plate.
• the sub-images join essentially edge-to-edge to each other.
• the total image that is present in the image plane exhibits a considerable agreement with a similar image of a conventional optical equipment.
• light beams from light cones a distance in front of the focusing plate will give rise to an unsharpness, called a "blur circle", and in consequence a loss of resolution.
• the blur circle is a pure geometrical effect caused by the light cones that are focused in front of the lens.
• the opaque sections of the focusing plate produce the effect that the unsharp light cones are cut off and chopped into smaller sub cones of light.
• Sharp patterns such as sharp edges, lines or dots, in arbitrary sections of the image space are converted into periodic patterns of some degree of sharpness (cf. Fig. 8).
• the focusing plate is coupled to a suitable means for position registering in order to determine its position with respect to the lens.
• a suitable means for position registering in order to determine its position with respect to the lens.
• Such position adjusting and position registering means are known to anyone skilled in the art, and is for example obtainable from Melles Griot AB, Taby, Sweden, or from Physik Instrumente GmbH & Co, Waldbronn, Germany.
• the focusing plate is rotatable around the optical axis of the lens, thereby allowing alternation of depth dependent blur patterns while keeping focusing distance constant, which alternations can be analysed. It is not new in itself to introduce a rotatable plate in an optical path and suitable means for this, with or without position read-out feed back, are available from Melles Griot.
• exposure has been used to represent a reproduction for a specific setting of the focusing plate according to the present invention. Although this expression suggests a reproduction obtained with a camera, the expression “exposure” should be understood to include visual perception through an eyepiece of the light in the image plane associated with a selected setting of the focusing plate.
• FIG. 10 is illustrated an embodiment of the present invention, for example adapted to endoscopic applications, wherein light is guided from the image plane IP to the eyepiece 6 via a fibre optical waveguide 7.
• the present invention makes it possible to analyse a series of sections of the image space being present between a lens and an eyepiece along the optical axis, as compared to previously known plenoptical equipment that only allows a single section in a corresponding image space to be analysed.
• the present invention is adapted to reproduce a readily visible image of the scene to which the lens is directed.
• the apertures of the focusing plate are combined with a transparent and coloured material, thereby enabling wavelength-associated analysis.
• a transparent and coloured material thereby enabling wavelength-associated analysis.
• Such an embodiment could, for example, be practised by forming the focusing plate as a thin cover plate, in which apertures are formed, disposed adjacent to a continuous coloured transparent sheet of glass or plastic. In a corresponding way, it is possible to provide a polarising filter.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Lenses (AREA)
• Telescopes (AREA)
• Focusing (AREA)
• Microscoopes, Condenser (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

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Cited By (1)

Citations (1)

• 1999
  • 1999-01-05 SE SE9900019A patent/SE517120C2/sv not_active IP Right Cessation
• 2000
  • 2000-01-03 AU AU21394/00A patent/AU2139400A/en not_active Abandoned
  • 2000-01-03 EP EP00901351A patent/EP1149315A1/en not_active Withdrawn
  • 2000-01-03 JP JP2000592673A patent/JP2002534706A/ja active Pending
  • 2000-01-03 WO PCT/SE2000/000004 patent/WO2000041010A1/en not_active Application Discontinuation

Patent Citations (1)

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