WO2004049031A1

WO2004049031A1 - Portable microscope

Info

Publication number: WO2004049031A1
Application number: PCT/GB2003/005156
Authority: WO
Inventors: Keith James Dunning
Original assignee: Dickinson, Richard, John
Priority date: 2002-11-28
Filing date: 2003-11-27
Publication date: 2004-06-10
Also published as: GB0227872D0; AU2003286270A1

Abstract

A portable microscope has a disc-shaped casing (1) with a flat face (2) acting as a sample stage. Light (4) from a sample adjacent the stage (2) passes through a viewing port (3) and is reflected by a first mirror (5) into a path parallel to the face (2). It then passes through an objective lens (6), two further mirrors (7, 8), a field lens (9) and an eye lens (10) to an observer's eye, its path being folded into a compact z-shape remaining parallel to the stage (2). The objective lens (6) is moveable along the light path to focus the microscope at a selected height relative to the stage (2). A generally annular light guide (15) is provided, encircling the viewing port (3) within the casing (1), which receives light from a white LED (14) and projects it in a converging cone through the viewing port (3) to illuminate the sample.

Description

PORTABLE MICROSCOPE

The present invention relates to a portable microscope. More particularly but not exclusively, it relates to a compact microscope, suitable for field use, with an integral sample illumination system.

Conventional bench-top microscopes are not particularly suitable for field use, for example for studying biological samples (such as pond life, insects or plant structures) or geological samples (such as soil structure or details of fossils). They are also unsuitable for examining items in situ, such as lichens on a rock, the surface of the rock itself, or corrosion pitting or stress microfractures on a metallic structure.

There have hence been attempts in the past to create more compact, portable microscopes by the use of angled mirrors and/or prisms, positioned in the light path between the microscope's lenses to fold the light path, so that the entire microscope can be contained within a compact, portable casing. However, such microscopes have suffered from difficulties in suitably illuminating the sample, and have also tended to suffer from relatively restricted fields of view, compared to conventional instruments.

A microscope as disclosed in European Patent Application No. 0361889 is known to solve some of such problems, but still has a number of practical shortcomings. The body of this microscope has a circular face with a viewing port therein which acts as a sample stage. Light from a sample thereon passes down through the port to a first angled mirror, which reflects it towards a x8 magnification objective lens. After passing through the objective lens, the light is reflected off two further angled mirrors within the microscope body before reaching an eyepiece providing a net magnification of xlO. The microscope hence provides an overall magnification of x80, or x 160 when a supplementary x2 lens is inserted into the light path between the two further mirrors. Sample illumination is provided by a battery- powered light bulb mounted on a boom pivotable between a position in which it illuminates thin and/or transparent samples from above, and one in which it projects light across an interior of the microscope body to another angled mirror, adjacent an underside of the viewing port, to illuminate the sample from below.

In practice, the utility of such microscopes is restricted by depth of focussing limitations. Light from the sample must travel from the viewing port to the first mirror and thence to the objective lens, restricting how closely the objective lens can approach the sample, to focus the microscope thereon. In practice, the first angled mirror must be positioned very close to an underside of the viewing port and the objective lens must be of restricted diameter so that it can be moved close to the mirror. The light path through the objective lens is hence slanted downwardly from the first mirror, and the angled mirror after the objective lens must be precisely aligned about two axes to align the remainder of the light path parallelly to the face of the microscope body. This complicates manufacture, and also restricts the field of view and light-gathering power of the microscope. Even so, this microscope can only be focussed on a point immediately above the viewing port, limiting its usefulness for examining samples with significant surface relief.

It has also been found that the illumination arrangement described for lighting opaque samples from below is not particularly efficient. Coupled with the small aperture of the objective lens, this can lead to unsatisfactorily dim images.

Thus, there is still a need for a compact microscope, usable in the field, which is better suited for examining solid and/or opaque samples.

It is hence an object of the present invention to provide a compact microscope having folded optics which obviates the above disadvantages and allows convenient microscopic examination of opaque and/or three-dimensional samples.

According to a first aspect of the present invention, there is provided a microscope comprising substantially planar sample stage means having viewing port means extending therethrough and which is provided with sample illuminating means comprising a light source and light directing means adapted to project light in a plurality of substantially different directions through the viewing port means on to a sample.

Preferably, the microscope comprises an optical arrangement defining a compactly folded light path extending substantially in a single plane between an objective lens means and an eyepiece lens means thereof. Advantageously, the compactly folded light path extends substantially parallelly to the sample stage means.

The microscope may comprise a reflecting element to direct light entering the microscope through the viewing port means into the objective lens means.

Preferably, the light directing means comprises a generally annular light guide, mounted substantially concentrically with the viewing port means and adjacent an internal surface of the sample stage means.

The generally annular light guide may have an internal circumference thereof bevelled at an angle to direct light emitted therefrom along a converging cone extending through the viewing port means.

The light guide may be provided on its outer circumference with a planar window through which light is directable into the light guide.

The light guide may be adapted to project light on to the sample having intensity greater in a first direction than light projected on to the sample in other directions, in order to accentuate surface relief of the sample.

The light guide may optionally be partially silvered to prevent light exiting therefrom except through said bevelled inner circumference. The light source is preferably white-light emitting diode means.

According to a second aspect of the present invention, there is provided a microscope comprising substantially planar sample stage means having viewing port means extending therethrough, and an optical arrangement comprising objective lens means, eyepiece lens means and a plurality of reflecting elements, wherein a first reflecting element directs light entering the microscope through the viewing port means into the objective lens means and a remainder of the reflecting elements define a compactly folded light path extending substantially in a single plane between the objective lens means and the eyepiece lens means.

Preferably, the plane of the sample stage means and the plane of the folded light path are substantially parallel one to the other.

Advantageously, said optical arrangement is housed within casing means, one surface of which comprises the sample stage means.

A principal axis of the objective lens means may be substantially parallel to a principal axis of the eyepiece lens means.

The reflecting elements may comprise mirror elements, preferably planar mirror elements.

Alternatively, the reflecting elements may comprise prism means.

The objective lens means may be selectably moveable along its principal axis, to focus the microscope on a selected portion of a sample. The sample stage means may be provided with retaining means to hold a sample to the viewing port means.

Said retaining means may be magnetic retaining means, and the sample stage means may then comprise a ferromagnetic material such as steel.

The eyepiece lens means may be detachable from the microscope to be usable as a hand lens.

The eyepiece lens means may comprise a field lens and an eye lens.

The eyepiece lens means preferably provides a magnification of between x5 and xl5, advantageously of around xlO.

The objective lens means preferably provides a magnification of x5 or less, advantageously of around x 4.

The microscope may be provided with sample illuminating means as described in the first aspect above.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is a schematic perspective view of a microscope embodying the invention, partially cut away to show the optical components thereof; Figure 2 is an alternative perspective view of the optical components of the microscope of Figure 1 and an optical path therethrough;

Figure 3 is a plan view of the optical components and optical path of Figure 2;

Figure 4 is a side elevation of the optical components and optical path of Figure 2;

Figure 5 is a plan view of a light guide isolated from the microscope of Figure 1;

Figure 6 is a cross-sectional view of the light guide of Figure 5, taken along the line

VI-VI; and

Figure 7 is a side elevation corresponding to Figure 4, with the light guide of Figure

5, the sample stage and a sample in place.

Referring now to the Figures and to Figure 1 in particular, a portable microscope comprises a generally disc-shaped casing 1. A clear viewing port 3 extends through the centre of one generally circular face 2 of the casing 1, the face 2 adjacent the viewing port 3 acting as a sample stage on which samples to be examined with the microscope may be positioned. The portion of the face 2 acting as a sample stage comprises a steel panel, allowing samples to be held to the viewing port 3 with a magnetic sample holder (not shown). A major portion of the casing 1 comprises ABS (acrylonitrile-butadiene-styrene copolymer) or another impact- resistant plastics material.

A path traced by a light ray passing through the microscope is shown by arrows 4. Light reflected from or transmitted through a sample enters the microscope through the viewing port 3, and is reflected from a first mirror 5. The first mirror 5 is mounted at an angle of 45° to the plane of the face 2, so that the ray 4 now travels parallelly to the face 2. The ray 4 passes through an objective lens 6 to a second mirror 7. The second mirror 7 reflects the ray 4, still parallelly to the face 2, towards a third mirror 8. The third mirror 8 reflects the ray 4, again parallelly to the face 2, towards a field lens 9, from which it passes to an eye lens 10 and thence to an eye of an observer.

The objective lens 6 provided four-fold magnification, while the field lens 9 and the eye lens 10 together form an eyepiece providing ten-fold magnification. The microscope thus provides forty-fold image magnification overall.

The objective lens 6 is moveable towards or away from the first mirror 5 by means of a mechanism operated with a thumb wheel (not shown), to allow adjustment of the focus of the microscope. The eyepiece comprising the field lens 9 and the eye lens 10 is removable as a unit from the microscope, and can be used as a hand lens providing ten-fold magnification. The eyepiece is provided with a detachable eye cup 11 of flexible plastics material.

A switch 12 is provided on the casing 1 to control the illumination arrangement of the microscope (omitted from this view for clarity).

The first mirror 5, objective lens 6, second mirror 7, third mirror 8, field lens 9 and eye lens 10 are all arranged in the same plane, allowing an overall height of the casing 1 to be kept to a minimum, as well as simplifying the microscope's internal structure. It is found that combining a relatively low-powered objective lens 6 with a higher-powered field lens 9/eye lens 10 combination allows focussing of the microscope over a range of heights above the sample stage. The first mirror 5 and the objective lens 6 may thus be positioned in the same plane as the other optical components 7, 8, 9, 10, rather than being crammed in close to the viewing port 3, as in previous microscopes. This also allows the use of an objective lens 6 having a greater aperture than hitherto, improving image brightness. The wider field of view of a four-fold magnification objective lens 6 is a further benefit and it has been found in practice that a forty-fold overall magnification is quite sufficient for most uses in the field, the eighty-fold or one-hundred- and-sixty-fold magnification of previous microscopes rarely being necessary.

Figure 2 shows an alternative perspective of how light travels through the microscope. In Figures 2, 3, 4 and 7, instead of the single ray 4 of Figure 1, a beam 13 of light is shown, representing an entire image passing through the microscope.

Thus, the beam 13 passes into the microscope through the viewing port 3 (not shown) and is reflected from the first angled mirror 5 towards the objective lens 6, which is continuously moveable between a first position 6A and a second position 6B, for focussing purposes. The beam 13 travels from the objective lens 6 to the second mirror 7, which reflects it towards the third mirror 8, which in turn reflects it towards the field lens 9 of the eyepiece. The beam 13 then travels through the field lens 9 and the eye lens 10 to the eye of the user.

As is shown by Figure 3, the path traced by the beam 13 is compactly folded with the principal axes of the objective lens 6, the field lens 9 and the eye lens 10 extending parallelly one to the other. This is a much more compact arrangement than the equivalent conventional microscope in which the lenses 6, 9, 10 are arranged along an elongate single common axis.

he eyepiece may be replaced by an adaptor to allow the microscope to be connected to a conventional camera (e.g. a 35mm film SLR camera), a digital camera or a camcorder, or by a digital coupler using CCD or CMOS imaging technology, connectable directly to a computer, e.g. by a USB cable.

Figure 4 shows how the arrangement substantially in a single plane of the lenses 6, 9, 10, the mirrors 5, 1, 8 and the beam 13 passing therethrough allows the height of a casing 1 (not shown) enclosing them to be kept to a minimum. The field lens 9, normally the largest- diameter optical component of a microscope, is here substantially square in cross-section, being dimensioned to correspond to a maximum extent of the beam 13. This again allows the height of the casing 1 to be minimised.

With the larger aperture and wider field of view of the objective lens 6, compared to earlier microscopes, it has been found that ambient light is usually sufficient to illuminate in transmission transparent samples presented to the viewing port.

Figures 5, 6 and 7 show the lighting arrangement used to illuminate opaque samples in reflected light. A white light emitting diode (LED) 14 is powered by conventional dry cell batteries stored within the casing 1 , by means of a voltage stepping circuit. In a preferred embodiment, the voltage stepping circuit is adapted to increase the voltage supplied by two conventional AA dry cell batteries (nominally rated at 1.5V each but in practice supplying 2.8V between them) to the 3.6V required by current white LEDs. Light from the diode 14 is passed into a generally annular light guide 15 through a plane window 16 in its outer circumference.

The light guide 15 has a raised circular rim 17 around its central aperture 18, which has a bevelled facet 19 from which light passed into the light guide 15 is emitted. This light is emitted generally normally to the bevelled facet 19, and so forms a hollow cone above the central aperture 18 of the light guide.

Figure 7 shows how the light guide 15 is used to illuminate a solid sample 20 positioned on the face 2 of the casing 1 above the viewing port 3. The light guide 15 is positioned below the viewing port 3, its central aperture 18 being concentric therewith. Light emitted from the light guide 15 passes out through the viewing port 3 and falls on an underside of the sample 20. Light 13 reflected therefrom may pass back through the viewing port 3 and the central aperture 18 of the light guide 15 to the first mirror 5, and travels through the microscope as described above.

This arrangement gives excellent illumination of the whole field of view of the microscope, without obstructing the optics thereof. The light guide 15 may be arranged so that there is a slight bias in the brightness of the illumination in one predetermined direction. There is a convention in reflected-light microscopy that a sample should be lit (or appear to be lit) from the "top left" comer (as perceived through the eyepiece), giving slight directional shading to emphasise surface relief.

The microscope described above is thus of sufficient power for field use, has a good field of view, can be focussed over a useful range of distances from its viewing port, and can provide its own reflected illumination for opaque samples while producing a sufficiently bright image from transparent samples using ambient light. The microscope can provide all these benefits within a compact, robust casing, easily transportable in a pocket, pack or the like to where it is needed and requiring no special preparation for use.

Claims

1. A microscope comprising substantially planar sample stage means having viewing port means extending therethrough and which is provided with sample illuminating means comprising a light source and light directing means adapted to project light in a plurality of substantially different directions through the viewing port means on to a sample.

2. A microscope as claimed in claim 1, comprising an optical arrangement defining a compactly folded light path extending substantially in a single plane between an objective lens means and an eyepiece lens means thereof.

3. A microscope as claimed in claim 2, wherein said compactly folded light path extends substantially parallelly to the sample stage means.

4. A microscope as claimed in either claim 2 or claim 3, comprising a reflecting element to direct light entering through the viewing port means into the objective lens means.

5. A microscope as claimed in any one of the preceding claims, wherein the light directing means comprises a generally annular light guide, mounted substantially concentrically with the viewing port means and adjacent an internal surface of the sample stage means.

6. A microscope as claimed in claim 5, wherein the generally annular light guide has an internal circumference thereof bevelled at an angle to direct light emitted therefrom along a converging cone extending through the viewing port means.

7. A microscope as claimed in either claim 5 or claim 6, wherein the light guide is provided on its outer circumference with a planar window through which light is directable into the light guide.

8. A microscope as claimed in any one of claims 5 to 7, wherein the light guide is adapted to project light on to the sample having intensity greater in a first direction than light projected on to the sample in other directions, in order to accentuate surface relief of the sample.

9. A microscope as claimed in any one of claims 5 to 8, wherein the light guide is partially silvered to prevent light exiting therefrom except through said bevelled inner circumference.

10. A microscope as claimed in any one of the preceding claims, wherein the light source is white-light emitting diode means.

11. A microscope comprising substantially planar sample stage means having viewing port means extending therethrough, and an optical arrangement comprising objective lens means, eyepiece lens means and a plurality of reflecting elements, wherein a first reflecting element directs light entering the microscope through the viewing port means into the objective lens means and a remainder of the reflecting elements define a compactly folded light path extending substantially in a single plane between the objective lens means and the eyepiece lens means.

12. A microscope as claimed in claim 11, wherein the plane of the sample stage means and the plane of the folded light path are substantially parallel one to the other.

13. A microscope as claimed in either claim 11 or claim 12, wherein said optical arrangement is housed within casing means, one surface of which comprises the sample stage means.

14. A microscope as claimed in any one of claims 11 to 13, wherein a principal axis of the objective lens means is substantially parallel to a principal axis of the eyepiece lens means.

15. A microscope as claimed in any one of claims 11 to 14, wherein the reflecting elements comprise mirror elements, preferably planar mirror elements.

16. A microscope as claimed in any one of claims 11 to 14, wherein the reflecting elements comprise prism means.

17. A microscope as claimed in any one of claims 11 to 16, wherein the objective lens means is selectably moveable along its principal axis, to focus the microscope on a selected portion of a sample.

18. A microscope as claimed in any one of claims 11 to 17, wherein the sample stage means is provided with retaining means to hold a sample to the viewing port means.-

19. A microscope as claimed in any one of claims 11 to 18, wherein the eyepiece lens means is detachable from the microscope to be usable as a hand lens.