WO1989001642A1

WO1989001642A1 - A cine photomacrography system

Info

Publication number: WO1989001642A1
Application number: PCT/AU1988/000310
Authority: WO
Inventors: Owen Seymour Scott
Original assignee: Owen Seymour Scott
Priority date: 1987-08-18
Filing date: 1988-08-18
Publication date: 1989-02-23

Abstract

An accessory for use with a microscope or other optical system and a camera to record or observe static or moving scenes clearly in focus over a depth of field many times that possible without it, and in some embodiments to allow control of perspective. The axial position of the plane in focus is changed continuously by the changing power of a rotating optical component (1) or set of lenses interposed between the microscope (10) and the scene (7). Illumination is arranged through a synchronously rotating slit (3) so that only the plane instantaneously in focus is illuminated.

Description

A CINE PHOTOMACROGRAPHY SYSTEM 1 INTRODUCTION

The invention provides improved depth of focus for optical systems such as microscopes and copiers. The improved depth of field allows the clear photography of both static and moving scenes and the observation or videp recording or cine photography of these scenes with detail in focus over a depth of field many times that obtainable without the system. "Depth of field " is generally accepted to be the axial distance between the nearest and furthest points of acceptable focus. For the most stringent focus requirements the depth of field is the axial distance over which there is no detectable change in image clarity from that at the position of best focus.

The invention is an accessory which can be used with a microscope or other optical system together with a camera or cine camera or video camera or the human eye to record or observe scenes clearly in focus over a depth of field exceeding that possible without the accessory. The need for increase of depth of field can be appreciated most readily by observing photographs taken with ultra close cameras (photomacnographs) or with microscopes (photomicrographs ). For example photographs of small insects generally have one plane in focus but parts closer or further from the camera can be seen to be blurred. The invention also allows control of perspective by changing the magnification as well as depth of field. If special steps are taken to keep magnification constaπtøhe presentation is "axonometric" and particularly useful for metrology from the records. 2 PRIOR ART

a) Depth of field for good quality optical systems used at the same magnification (image size divided by object size) does not depend on lens focal length. Improvements in depth of field can be obtained by using a larger f-number. (a smaller stop). However, increasing the f-number decreases the tight available from the object to the image. A compensatory increase in object illumination can provide sufficient brightness of the image. The need for increased illumination reaches a practical limit when lighting systems become too bulky, or when heating of the object affects its shape or in the case of living organisms, when the organisms are killed.

b) Depth of field for static objects can be increased by a scanning system Illumination in the form of a thin sheet of light is used in a plane perpendicular to the optical axis of the optical system. The thickness of the sheet of tight is controlled by a slit also in the plane perpendicular to the axis. The thickness of the sheet is controlled to match the depth of field of the optical system as it is without the scanning system. The slit is clamped to the microscope or other optical system and the object is moved slowly along the optical axis. Each section of the object is illuminated and in focus at the same time during this movement All parts of the object instantaneously out of focus are not illuminated. A still camera with its shutter open during the scan is attached to the microscope eye piece. If records the whole of the object in focus on the film. 3. PROBLEMS TO BE OVERCOME

Solid objects, or objects set in a gel may be moved up and down along the optical axis sufficiently rapidly so that video or cine photographs of the objects can be obtained or they can be viewed continuously without flicker. The movement at about 50 cycles per second or more could adversely affect small living things and objects suspended in liquid Such up and down movement of the object can be avoided by keeping the object stationary and moving the combined slit and microscope. The adverse affects of such vibration on the equipment, and the power required are obvious disadvantages of this approach.

The problem to be overcome is the provision of up-and-down movement of the sheet of light along the optical axis (the sheet being perpendicular to the optical axis) and, in synchronism, moving the plane of focus of the optical system so that the focal plane and the illuminated plane coincide continuously, without any movement of the microscope and viewing system (human eyes, video camera or cine camera),and without any need for externally caused movement of the object under study. 4 OBJECT TO BE ACHIEVED The object is to provide a moving sheet of light perpendicular to the optical axis of an optical system such as a microscope, with the movement being up and down (or up only or down only) along the optical axis, and in synchronism to move the effective focal plane of the optical system to correspond to the position of the sheet of light continuously. The sheet of light can be of constant intensity or can be pulsed or modulated to match any discontinuity in the movement of the focal plane. For example the sheet of light can be positioned at a number of discrete axial positions so that the required depth of field is covered in a sufficiently small period to avoid flicker, and the sheet of light can be switched off for periods when the depth of field is being changed from one position to the next. The overall objective is to scan the object either continuously or in discrete steps with both a sheet of light perpendicular to the optic axis of the optical system and the focal plane of that optical system, with the sheet of light and the focal plane coincident for all periods when the sheet of light is present, and to perform the scan sufficiently rapidly for fiickeriess visual observation, video recording or cinephotography through the optical system. The result of achieving this objective is the visual presentation of the object under study with the clarity associated with the normal depth of field of the optical system but over a total depth of field many times that of the normal depth of field The achievement of this increased depth of field is advantageous in many fieles such as biology, chemistry, medicine, and cinematography in which moving scenes need to be observed at high magnification and/or at high resolution, and in which the simple vibration of the object is not acceptable. Subsidiary objectives are to provide the observation recording or filming of moving or static scenes at specific perspectives or with constant magnification. 5 BROAD DESCRIPTION

The invention is a combination of an optical component or set of components and an illumination system /with the optical component or components interposed between the object to be viewed or cinephotographed or video recorded and the microscope or other viewing system, and with the illumination system providing illumination only in the instantaneous focal plane of the combined optical system and optical component. If one observes a small object through a microscope, and then interposes a flat plate of glass (equivalent to the "optical component") between the object and the microscope objective lens, then the object becomes blurred The plate of glass moves the focal plane of the microscope away from the objective lens and in order to refocus on the object the microscope has to be moved axially away from the object, or the object has to be moved away from the microscope. Interposing the plate of glass moves the focal plane (the plane in focus) away from the microscope. The axial movement d of the plane in focus is given by d = (u - 1) t where u is the refractive index of the glass and t its thickness. The axial position of the plane of focus can be changed continuously by changing the thickness of the glass, for example by rotating a cylindrical wedge of gjass, vibrating a wedge of glass to-and-fro across the optical axis, or successively interposing lenses of a range of focal lengths in the space between the microscope objective lens and the object to be viewed The axial movement of the plane of focus could also be obtained using a stationary deformable lens containing a fluid with the deformation (for example by changing the pressure on the fluid) controlled so that the power of the lens changed to provide the focal plane movement The axial position of the sheet of light can be changed by providing a static parallel beam of figjht perpendicular to the optical axis over the whole of the object to be viewed and blocking aH but the sheet currently required to match the plane in focus by using a slit perpendicular to the parallel beam and in the plane in focus. The slit is moved up and down across the parallel beam (or up only or down only) in synchronism with the plane in focus so that only the plane instantaneously in focus is illuminated If a series of lenses is used to change the axial position of the plane in focus then both the focal length and the axial position of each lens has to be selected if constant magnification is required A range of focal lengths can however be chosen so that magnification varies with axial position over the total depth of field For example a view of an ant could be obtained from the point of view of an observer just in front of its head by having the ant facing the microscope objective and arranging the magnification to decrease with distance from the objective. This technique would provide a simulation of a static or moving insect or small object of any type at any perspective required Such a technique would be appropriate for special effects in cinematography, for example for representing giant insects by real insects. For most scientific uses the magnification would be chosen to be constant so that metrology could be carried out easily on the recorded images. 6 EXAMPLES a) One method of realizing the invention is illustrated in figure 1. 1 is a transparent cylindrical wedge of refractive index greater than air, with the flat faces of good optical flatness. 2 is an opaque drum with a transparent slit 3 in a helical form from the top 4 at one side of the drum to the bottom 5 at the other side and with axial position in the slit a linear function of angular position. Both the cylindrical wedge and the cylindrical drum are mounted on the same spindle 6 which can be turned directly by a motor or by a belt drive from a remotely mounted motor, (not shown). The drum and wedge are fitted together with the point 5 at the same angular position about the spindle axis as the thickest part of the wedge. Parallel light from an external source is directed into the drum from below and reflected towards the working space 7 by the static plane mirror or set of plane mirrors 8. The reflected light 9 emerges into the woridng space normal to the axis of the rotating system and normal to the axis of the microscope 10 being used to observe the working space. As the motor turns the spindle the attached wedge and drum rotate. The lower parts of the working space are illuminated when the thickest part of the wedge is above the working space, and the highest parts when the thinnest parts of the wedge are above the woridng space. The illumination system can incoiporate an optical filter to provide monochromatic illumination to avoid chromatic aberration in the wedge. Conversely the wedge can be a composite of two wedges of two different refractive indeces chosen to correct chromatic aberration in the well known manner. (For example by incorporating an additional wedge 12 with thickness maximum where wedge 1 has minimum thickness) Rotation is made sufficiently rapid to prevent flicker effects in the observing system. b) A method of realizing the invention by rotating a series of lenses instead of a wedge is illustrated in figure 2. The series erf lenses 1 replaces the wedge of figure 1. The drum 2 is similar to the drum 2 of figure 1 but it has horizontal slits 3 each corresponding to the angular position of one lens and at an axial position to provide illumination at the plane of focus below that lens. The lenses 1 have different focal lengths and are placed at axial positions which are defined by the presentation requirements. The lens makers formula and the formula for lateral magnification are all that are needed for the calculation of the focal length and axial position of each lens. Any perspective can be provided in the display or film or recording by the appropriate choice of these parameters. Illumination can be provided in the same way as for example 1 for example by the mirror or mirrors 8 and the parallel light source 6. However the illumination is best made intermittent in this embodiment by arranging a bright flash at the moment when each lens is directly above the working space. Additional flashes can be provided at times before and after the time when each lens is directly above the woridng space to assist in avoiding flicker effects, and to add to total illumination. The lenses can be chromatically corrected in the accepted way so that white light can be used without chromatic aberration; or the lenses can be of one refractive index and monochromatic light used; or the chromatic aberration may be tolerated without correction. The timing of the flashes can be synchronised to the correct angular position by using a static electro-optic pick-off operating through holes 9 in the drum positioned at the angular points where the flashes are required. The source of the pick-off is positioned on one side of the drum wall and the detector on the other so that when a hole appears between them a line- of-sight exists between receiver and source and the flash is triggered. c) The wedge of example a) can be replaced by a wedge of a different form which is illustrated in figure 3. The thickness of the wedge is a maximum at 1 and a minimum at 2 and is a linear function of angular position about the axis 3-3.

All of the examples a), b), and c) require mechanical balancing with a compensating component or set of components with weight distribution chosen so that the system can rotate at high speed without vibration. A case can be used to surround the system for safety in the event of a component becoming loose. The case would require a window or aperture below the microscope objective and where the light beam enters the system. The case would also provide a degree of sound insulation and would reduce air movement caused by the rotation. For all embodiments requiring illumination from more than one direction, static reflectors can be used to direct tight to the object as illustrated in figure 4. The figure is in the plane of illumination. The plane mirrors 4 and 5 extend through the axial extent of the total depth of field to be covered by the system. To cover an object of linear dimensions about 2 miliimeters for example stits of 6 millimeters length are required. The outer 2 miltimeter sections are reflected by mirrors 4 and 5 at 60 degrees to the direction of illumination . The object is then illuminated equally from three directions at 120 degrees separation.

Claims

1 CLAIMSThe claims defining the invention are as follows.

1. An accessory for use with a microscope or other optical system comprising a means of illumination limited to the plane in acceptable focus, means of changing the plane of illumination either continuously or intermittently, means of changing the plane in focus either continuously or intermittently and with the means of changing the plane in focus arranged to make that plane in focus correspond to the plane being illuminated at all times when the illumination is presented with the means of changing the plane in focus and being illuminated arranged to scan or sweep the subject being observed, fibned, or video recorded by the microscope or other optical system in a direction perpendicular or nearly perpendicular to the plane in focus and sufficiently rapidly to avoid flicker or blur in the observations, films, or records of the subject, and with the increase of depth of field achieved without vibration or other movement apptied to the subject or microscope or other optical system.

2. An arrangement according to claim 1 wherein means are included to correct for any chromatic or other aberration in the optical components comprising the means of changing the plane in focus.

3. An arrangement according to claims 1, or 2, wherein means are inchided to provide magnification either ccmstant throughout the extended depth of field or magnification varying with axial position in the extended depth of field to provide a representation of the subject at any required perspective.

4. An arrangement according to claims 1, 2, or 3, wherein means are inchided to ensure that rotating components are balanced by compensating mechanical components to allow high speed rotation without vibration.

5. An arrangement according to claims 1, 2, 3, or 4, in which the illuminating system incorporates static optical components to direct the illumination to the subject from an additional direction or directions in the plane of illumination.

6. An arrangement according to claims 1, 2, 3, 4, or 5 in which a case is provided for safety purposes and to reduce any sound and air movement which could be inconvenient to the operator.

7. An accessory for use with a microscope or other optical system to provide significant increase of depth of field and/or perspective control substantially as described and illustrated in the following drawings.