GB2184562A

GB2184562A - Liquid or semi-solid lens or mirror with system for adjusting focal length

Info

Publication number: GB2184562A
Application number: GB08629355A
Authority: GB
Inventors: Joshua David Silver; Michel Treisman
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-12-10
Filing date: 1986-12-09
Publication date: 1987-06-24
Also published as: GB2184562B; GB8629355D0

Abstract

An adjustable liquid lens or mirror comprising a chamber 10 delimited by a flexible membrane surface 1, 6, a first fluid medium filling the chamber which, in the case of a lens, has a different refractive index from that of a second fluid medium contacting the other side of the flexible membrane, and an annular support member 2 for the flexible membrane comprising relatively movable first 3 and second 7 component parts, the first and second component parts of the support member being adjustably linked in a fluid-tight manner, via 12, whereby the volume of the chamber 10 is adjustable by moving one component part of the support member relative to the other in such wise as to vary the pressure in the first fluid medium and thereby to alter the shape of the said membrane surface 1, 6. <IMAGE>

Description

SPECIFICATION Liquid or semi-solid lens with intrinsic system for adjusting focal length Technical field This invention relates to a new design of liquid lens, the focal length of which can be altered by relative movement between component parts ofthe lens holder. The invention also relates to an adjustable focus mirror.

Background of the invention A lens is an object, usually made of glass, shaped so that it will transmit electromagnetic radiation coming from a source (the "object") and focus that radiation into an "image" at another location in a way that preserves the spatial distribution in the source. A lens is commonly made of one or more solid pieces of material, such as glass or plastics, transparent to the radiation to be passed through it.

A liquid lens is a radiation refracting element having at least one boundary surface defined by a flexible membrane delimiting a volume of liquid transparent to the transmitted radiation. In one simple embodiment, a liquid lens is a hollow flexible object having spaced-apart flexible membrane surfaces, which object is filled with a liquid of refractive index different from the gas(es) surrounding it, so that the shape it adopts depends on the positive or negative pressures of the liquid filling it. A liquid lens of adjustable shape will be referred to herein as a "lensat".The liquid filling the deformable hollow object is pressurised by a device such as a pump, or is supplied from a sealed reservoirwhich may be deformed byanysuitable external agent so as to varythe pressure in the lensat, so asto produce a suitable part-spherical or othercurved shape of one or both ofthe membrane surfaces to give the lensatthe property of functioning as a lens with an adjustable focal length.

Although a lens of adjustable focal length would have advantages, providing a facility for adjusting focal length from an external reservoir may present difficulties.

By making the membrane surface significantly reflective to the radiation incident on it, a mirror is created, and the invention also extends to an improved flexible membrane mirror.

Statementofthe invention According to the present invention, an adjustable liquid lens or mirror comprises a chamber delimited by a flexible membrane surface, a firstfluid medium filling the chamberwhich, in the case of a lens, has a different refractive index fro that of a second fluid medium contacting the other side ofthe flexible membrane, and an annularsupportmemberforthe flexible membrane comprising relatively movable first and second component parts, the first and second component parts ofthe support member being adjustably linked in a fluid-tight manner whereby the volume of the chamber is adjustable by moving one component part ofthe support member relative to the other in such wise as to vary the pressure in thefirstfluid medium and thereby to altertheshape ofthe said membrane surface.As the fluid medium, may be used a semi-solid or gelatinous substance such as gelatine.

In the case of an adjustable mirror, the first and second fluid media could be the same, sincethere need be no transmission of radiation through the first medium.

The component parts ofthe support member may be screw threaded together so that relative rotation of one in or on the other causes the required pressure change in a simple but well controlled manner.

In the case of a liquid lens having two spaced-apart flexible membrane surfaces delimiting the fluid-filled chamber, the relatively adjustable component parts of the membrane support member can be screw-threaded together over part of interengaging cylindrical surfaces with an 0-ring interposed between said surfaces, said O-ring defining a part of the boundary surface of said chamber, whereby rotation of one support member part relative to the other changes the pressure ofthe fluid within the chamber and thus effects a change in shape of each flexible membrane surface.

Briefdescription ofthe drawings The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure lisa purely schematic sectional side elevation of a first embodiment of liquid lens according to the invention, Figure2 is a viewsimilarto Figure 1 but of a two cavity liquid lens, Figure 3 shows a schematic exploded sectional side elevation of a third embodiment of liquid lens according to the invention, Figure 4shows a partly sectioned side view of the assembled liquid lens of Figure 3, and Figure 5shows, in schematic sectional view, a pair of spectacles with two liquid lenses according to the invention.

Description ofpreferred embodiments Figure 1 (not drawn to scale) shows one embodiment of adjustable power lens. An anterior flexible transparent membrane 1 is held in an outer part3 of an annular holder 2 between a pairof O-rings 4 and 5. This method of mounting a liquid lens membrane in a lens holder is described in our co-pending British Patent Application 8621290. A posterior membrane 6 is held in a similar manner in an inner part7 ofthe holder2 byafurther pairof O-rings 8, 9. The cavity 10 defined in the bore 11 of the holder between the membranes 1 and 6 isfiiled with a suitable liquid such as water, alcohol, gelatine or glycerol, and an 0-ring seal 12 prevents leakage of the filling liquid between the parts 3 and 7.The part7 screws into the part3 at 13. By screwing the holder part 7 towards or away from the holder part 3, the pressure in the cavity 10 can either be increased, causing the membranes 1,6 to flex outwardly and the liquid lens to become more positive, or reduced, causing the liquid lens to become more negative.

The medium in contact with the upper surface ofthe membrane 1 and the lower surface ofthe membrane 6would normally be air butitwill be appreciated this need not be the case. The bore 11 a could contain some other gas or even a liquid of different refractive indexfromthatfillingthecavity10.

The meansforturning part7 relative to part3 of the holder 2 to effect a lens power change can take manyforms. It cou Id, for exa mple, bea knurled ring 14 surrounding part3 and connected to part7 viva a rod 15 located in an arcuate slot 16 in the part3.

Displacement without rotation is also possible (e.g.

with an external screw clamp).

Figure 2 shows a rather more complex liquid lens having two liquid lenses one above the other. Where appropriatethesame reference numerals have been used in Figure 2 as were used in Figure 1 to designate similarintegers. The compound adjustable membrane autofocus lensat shown in Figure 2 has a third housing part 17 screw-threaded into the part7 with a separate O-ring seal 18.

Thethird part 17 supports an O-ring tensioned third membrane 19 which defines a second cavity 20 inside the bore 11 a. The third part 17 can be axially adjusted relative to the second part 7 to adjustthe pressure in the liquid filling the cavity 20. This adjustment could be by way of a ring 21 operating in a manner similarto that described aboveforthe ring 14. Since membrane 6 is now common to the cavities 10 and 20 adjustmentofthe pressure in one will have an effect on the power of the liquid lens defined by the other. This may be of advantage, but if not, can readily be compensated for by appropriate readjustment ofthe other ring 14 or 21. Different liquids can be used in the two cavities 10 and 20.

Figures 3 and 4 illustrate a lensat of a relatively compact design. As with the previous designs there are two transparent membranes (e.g. 23 micron thickness type D "Mylar" (RTM) material) 1 and 6 (shown only in chain lines) tensioned between respective pairs of O-rings 4,5 and 8,9. The housing 2 comprises a pair of annular members 22 and 23 which when interengaged with the membranes in place define a fluid-tight chamber of variable volume. The O-rings 4,5 are pressurised on either side ofthe membrane 1 by an annularfixing plate 22a and the O-rings 8,9 are pressurised on either side ofthe membrane 6 byan annularfixing plate 23a.Both fixing plates are tightened in place to tension the respective "MYLAR" membrane by means of a ring of screws (only shown schematically at24).

The annular members 22,23 are sealed in 'tiuid4ight manner by an O-ring 25 designed to be located in a groove 26 in a cylindrical outer surface 27 of the member 23.A part 28 ofthe surface 27 is screw4hreaded to mesh with a threaded part 29 of a second cylindrical surface 30 forming part ofthe member 22. The size ofthe O-ring 25 and the dimensions ofthe groove 26 in which it is located are selected (in known manner) to obtain sufficient deformation ofthe 0-ring to provide a good fluid-tight seal between the surfaces 27 and 30 but not so great a deformation asto make itdifficultto occasion relative rotation between the members 22, 23 when the power ofthe lensat is to be adjusted.

The chamber31 created in the member 22 bytheseal 25 and the membranes 1 and 6 could be filled with air-freedistilledwater32,forexampleasshown in Figure 4.

Figure 4 shows the third embodimentoflensat fully assembled and arranged to provide a negative double-concave lens. The liquid 32 filling the chamber 31 between the membranes 1 and 6 is at sub-atmospheric pressure, the pressure being adjusted by screwing the member 23 into or outof the member 22. Screwing in will reducethe power of the negative lens and screwing out will increase the powerofthe lens.

It will be seen therefore that the lensat constructions shown in Figures 1 to4each includes a piston-type arrangement in which one housing member moves as a sealed piston within the otherto provide a "pumpless" lensat.

In each ofthe lensat designs illustrated one ofthe membranes may be replaced by a substantially rigid solid fluid-tighttransparent member which may or may not havea powerdifferentfrom unity.

Atelephoto lens is a system of lenses designed to allow a camera to photograph a magnified image of distantobjects. Azoom lens is a system of lenses which can be adjusted by altering the physical arrangement of the lens components therein so asto alterthe overall focal length and field of view to give it telescopic or near-field propertiqs. Autofocus lenses of the kind described above may be used in place of solid lenses in a telephoto or zoom lens, telescope, binoculars, microscope, camera, or other optical device. They may be used in combination with fixed lenses. Thus a zoom lens can be constructed oftwo adjustable membrane autofocus lensats in sequence, one having a negative and the other a positive power.The relative positions ofthe lenses do not require to be altered in orderto change the focal length of the combination. This can be done by rotating the innerand outer partofthe holderof one or the other ofthe autofocus lensats.

Ifthe anterior surface of a liquid lens (say membrane 1 in Figure 1) is covered with a reflective coating, this produces a flexible membrane mirror.

By displacing the inner part 7 ofthe holder 2 in Figure 1, the focus ofthe membrane mirror 1 can be altered.

A mirrorofthis construction can be considered to be an autofocus membrane mirror.

A pair of spectacles is a device consisting oftwo lenses in a frame that allows the lenses to be worn before the eyes so as to correct errors of refraction or supplement deficient accommodation. Spectacles are traditionally made with solid lenses. These have the disadvantage that the focal length is restricted (in the case of a bifocal lens to two values) and is not adjustable on demand. Figure 5 illustrates one possible design for spectacles in which the solid lenses have been replaced by autofocus lensats. The frame (shown at 40 in Figure 5) incorporates two holders 2,2'. By rotating the inner parts 7 and 7' in the left and right lensats, the focus of each lensat can be adjusted overa continuous range of values to suit the eye ofthewearerfor an object of regard at a given distance.The frame 40 may attach directly to the part 7, in which case the outer part 2 fit on to part7 by a screw- or slide-fitting.

Discs 41 and 42 of transparent unbreakable plastic or glass may be fixed to the rear and front of each lensat holder so as to protectthe flexible membranes 1 and 6 from dirt and damage. The discs 41 and 42 may be clip-on or otherwise removable attachments (e.g. bayonet or screw mounted), or they could be permanently attached. The discs 41 and 42 may themselves be solid lenses that provide a basic correction to vision which can be further adjusted by altering the focal lengths ofthe lensats. They may be planar, orthey may have a cylindrical surface to allow for the correction of astigmatism. The surfaces of one or both discs may be so shaped as to correct for any aberrations associated with the liquid lens over a range of focal lengths.They may be transparent or tinted (e.g. light-intensity colour-controlled), so allowing the spectacles to be used as sunglasses of variable focus and variable tint. The spectacles of Figure 5 use lensats ofthe kind shown in Figure 1 but other designs are clearly possible.

This invention thus relates to novel types of liquid or semi-solid lenses which allow the focus of the lens to be altered directly by manipulating the relative positions of components ofthe holders of the lenses.

Such lenses may be constructed of at least one membrane and preferably a membrane held between O-rings. Direct variation in the volume of thechamberdelimited bythemembrane(s) maybe used to alter the internal pressure in the lens and so its focal length, giving a lens of directly adjustable focus. Such liquid lenses may be combined to produce compound lenses with both components separately adjustable or adjustable in some linked manner and they may be used to construct telescopes, zoom lenses, spectacles, cameras and a wide range of other optical devices.

If the means used for adjusting the pressure exerted on the membrane is calibrated in some way, the lensats described above can be used by an opthalmologist in determining the refraction of a patientorbyan optician in determining what power of spherical lens needs to be prescribed for each eye of a patient.

The calibration is conveniently arranged to read directly in dioptres but it is possible to have some other graduated scale and a reference cha rt to relate thescale reedingsto the appropriate lens power.

Thus the arrangements described could be used to provide the calibration by marking a scale on one memberand providingapointer,lineorother reference mark on the other, which moves along the scale as the lens power is changed.

It is envisaged that one or a few small disc-shaped lensats such as that shown in Figure 3 could be used as replacementforthe many fixed focus lenses nornially used in prescribing spectacles and for otheropthaimic purposes.

Further, if the focal length adjustment, in say the spectacles of Figure 5, is made sufficiently easy to operateand is manuallyaccessibletoa patient viewing through the lensat, the patient can adjust the focal powerto optimise the sharpness of focus he/she is experiencing during a test, thereby facilitating the selection of the correct lens power required to compensate for vision defects.

In case ageing of the membrane produces loss of calibration accuracy, a re-adjustment facility can be provided on each lensatto enable periodic re-calibration. Forexample,this could be a separate pre-settable pressure-adjusting means,orthe pointer referred to above could be capable of having its position of attachment to the housing adjusted.

Acylindrical Iensatofadjustablefocuscan be produced by using membranes of graded thickness and such lensats can be used to correct astigmatic errors.

It is also possibleto provide a lensatwith an at least partial cylindrical lens by trapping the flexible membrane between confronting O-rings held in respective grooves that follow cylindrical surfaces.

Thus, for example, the grooves accommodating O-rings4and 5 in Figure 1, ratherthan being coplanarasshown, can each Iieonacylindrical su rface, the O-ri ng 4(say) lying on afirstcylindrical surface ofa given radius and the 0-ringS lying on a second cylindrical surface of the same or substantiallythe same radius. In a pluri-chamber lensat, cylindrical components can be added to more than one ofthe membranes andthe axes ofthetwo or more different cylindrical components of the lens surfaces need not be parallel.The surfaces followed by a confronting pair of O-rings need not be cylindrical if they are non-planarthus leaving open the possibility offabricating complex lens surface contoursforspecificapplications.

Althoughthetensioned regions ofthe membranes disclosed thus far are circular in plan, there is no needforthisto bethe case and the invention should be seen to include non-circulartensioned membrane regions. In some applications a rectangular membrane could be used and such a membrane shape can be achieved either by using a rectangular O-ring (e.g. made from lengths of circularsection elastomeric rod mitre-joined at the corners) or by using a pair of circumscribing circularO-ringsto form the primaryseal of the cavity to the membrane and to tension the membrane but contacting the tensioned membrane within the bore of the O-rings buy a rectangular frame that defines the optical boundaryofthe lensat.

Claims

1. An adjustable liquid lens or mirror comprising a chamber delimited by a flexible membrane surface, a first fluid medium filling the chamber which, in the case of a lens, has a different refractive index from that of a second fluid medium contacting the other side of the flexible membrane, and an annular support memberfortheflexible membrane comprising relatively movable first and second component parts, the first and second component parts ofthe support member being adjustablylinked inafluid-tightmannerwherebythevolumeofthe chamber is adjustable by moving one component part ofthe support member relative to the other in such wise asto vary the pressure in the firstfluid medium and thereby to alterthe shape of the said membrane surface.

2. A lens or mirror as ciaimed in claim 1, in which the firstfluid medium is a transparent liquid.

3. A lens or mirror as claimed in claim 1, in which thefirstfluidmedium isasemi-solidorgelatinous substance.

4. A lens or mirror as claimed in any preceding claim, in which the component parts ofthe support member are screw-threaded together so that relative rotation of one in or on the other causes the required pressure change in thefirstfluid medium.

5. A liquid lens as claimed in claim 1,2 or3, having two spaced-apartflexible membrane surfaces delimitingthefluid-filled chamber, the relatively adjustable component parts of the membrane support member being screw-threaded together over part of interengaging cylindrical surfaces with an O-ring interposed between said surfaces, said O-ring defining a part ofthe boundary surface of said chamber, whereby rotation of one support member part relative to the other changes the pressure ofthe firstfluid within the chamber and thus effects a change in shape of each flexible membrane surface.

6. A liquid lens as claimed in claim 5, in which there are three flexible membranes defining two adjacentfluid-filling chambers formed in a housing having outer, middle and inner components, one of said chambers being defined in part by a seal formed between the outer and middle components and the other of said chambers being defined in part bya seal formed between the middle and inner components.

7. A liquid lens as claimed in claim 6, in which relative rotation is possible between the middle and outer components to vary the volume ofthe said one chamber and relative rotation is possible between themiddleandinnercomponentstovarythevolume of the said other chamber.

8. A lens or mirror as claimed in claim 1, in which the first and second component parts exhibit closely adjacent cylindrical surfaces between which an O-ring seal is located.

9. A lens or mirror as claimed in claim 8, in which the adjacent cylindrical surfaces each extend away from respective intermeshing screw-threaded parts.

10. The combination of a lens as claimed in any preceding claim with a further lens to provide a telephoto or zoom lens, a telescope, binoculars, a microscope ora camera.

10. A lens or mirror as claimed in any preceding claim, in which each membrane is held in place in its housing part between a compressed pairofO-rings.

11. A pair of spectacles comprising two liquid lenses as claimed in any preceding claim mounted in a frame.

12. The combination of a lens as claimed in any preceding claim with a further lens to provide a telephoto or zoom lens, a telescope, binoculars, a microscope or a camera.

13. A liquid lens substantially as hereinbefore described with reference to, and as illustrated in Figure 1, Figure 2, Figures 3 and 4 or Figure 5 ofthe accompanying drawings.

Amendments to the claims have been filed, and have the following effect: *(a) Claims 1,5,6,8,9,10 and 12 above have been deleted ortextuallyamended.

*(b) New ortextually amended claims have been filed asfollows: *(c) Claims 11 and 13 above have been re-numbered as 9 and 11 and their appendancies corrected.

1. An adjustable liquid lens or mirrorcomprising a chamber delimited by a flexible membrane surface, afirstfluid medium filling the chamber which, in the case of a lens, has a different refractive indexfromthatofasecondfluid medium contacting the other side ofthe flexible membrane, and an annularsupport memberfortheflexible membrane comprising relatively movable first and second component parts, the first and second component parts of the support member exhibiting closely adjacent cylindrical surfaces between which an O-ring seal is located and being adjustably linked in a fluid-tight mannerwherebythe volume ofthe chamber is adjustable by moving one component part of the support member relative to the other in such wise asto varythe pressure in thefirstfluid mediumandtherebytoaltertheshapeofthesaid membrane surface, the membrane defining said membrane surface being held in place between a compressed pairofO-rings.

5. A liquid iens as claimed in claim 1,2 or3, having two spaced-apartflexible membrane surfacesdelimitingthefluid-filledchamber,the relatively adjustable component parts ofthe membrane support member being screw-threaded together over part ofinterengaging cylindrical surfaces with an O-ring interposed between said surfaces, said O-ring defining a part of the boundary surface of said chamber, whereby rotation of one support member part relative to the otherchanges the pressure ofthe firstfluid within the chamberand thus effects a change in shape of each flexible membrane surface, each membrane defining a membrane surface being held in place in its respective support member between a compressed pair of O-rings.

6. A liquid lens as claimed in claim 5, in which there are threeflexible membranes defining two adjacentfluid-filled chambers formed in a housing having outer, middle and inner components, one of said chambers being defined in part by a seal formed between the outer and middle components and the other of said chambers being defined in part by a seal formed between the middle and inner components, the third membrane also being held in place between a compressed pairofO-rings.

8. A lens or mirror as claimed in claim 1, in which the adjacent cylindrical surfaces each extend away from respective intermeshi ng screw-threaded parts.