WO2007037691A2

WO2007037691A2 - Variable lenses for optical digital modules

Info

Publication number: WO2007037691A2
Application number: PCT/NL2006/050163
Authority: WO
Inventors: Michiel Christiaan Rombach; Gleb Vdovine
Original assignee: Michiel Christiaan Rombach; Gleb Vdovine
Priority date: 2005-07-01
Filing date: 2006-07-03
Publication date: 2007-04-05
Also published as: WO2007037691A3

Abstract

The invention relates to a variable lens comprising at least two optical elements, wherein at least one of the optical elements is movable in a plane transversely of the optical axis of the lens relative to the at least one remaining element, wherein at least two optical elements have a surface described by a polynomial of at least the third order, and wherein the curvature of the curved surfaces of the optical elements is such that at different relative positions of the displaceable optical elements the resulting lens has a differing strength. According to a first embodiment, the lens comprises at least one optical element having at least one surface described by z = SA (x,y) = A(x2y2 + x4 / 6). According to another embodiment, the lens comprises at least one optical element having at least one surface described by z = Sc(x,y) = C(x2y3 + x5 / 10).

Description

Variable lenses for optical digital modules

Digital cameras are general components of present and future consumer products. Digital cameras are also applied extensively in technical and military systems, security systems and the film industry. Digital sensors have now superseded conventional film in practically all cameras. The most significant advantages of the new generation of digital cameras are: a high resolution, high light-sensitivity, immediate digital image processing and digital storage of images, low production costs and the option of a great depth of field in the image.

The depth of field of optical systems could formerly only be increased in a traditional optical manner, i.e. by reducing the diameter of a diaphragm arranged in the optical system. Reducing the diameter of the diaphragm does however result in significant light losses and a degradation in resolution in the plane of projection. Depth of field is bears a proportional relation to the diameter of the diaphragm, but the amount of light transmitted has an inverse quadratic relation to this diameter. Increasing depth of field thus involves significant light losses. With a very small diaphragm additional physical effects occur, such as diffraction of the light, which can decrease the quality of the image still further. This conventional approach to increasing depth of field therefore has physical limits.

Using modern optical systems and the associated digital technology depth of field can be improved in different ways. A number of new optical digital technologies form the basis of this patent. These all combine unique properties of variable lenses with one or more sliding optical element lenses with digital image processing to arrive at a final image of high quality and great depth of field. A recording is usually made here which results in an intermediate image, this intermediate image being reconstructed via a digital processing into a final image.

The principles of variable lenses with two or more sliding optical elements, the use of digital technology in combination with lenses having two or more sliding optical elements, different ways in which the optical/digital combination can be applied in camera modules designated with technical terms such as wave front coding/decoding, temporal focus coding, plane selection/swap refocus and foveated focusing, are respectively considered.

It should be noted that variable lenses with one or more sliding optical elements traditionally usually comprise two cubic elements in accordance with the principle of Alvarez (US-A-3,305,294) or variations thereof. Other such variable lenses having inter alia elements with fourth order surfaces are possible and described in this patent, cubic elements with quintic corrections of aberrations are already long known (US-A-3, 583,790 and US-A-4, 650,292) and other optical solutions can also be envisaged. In the present patent variable lenses with curvatures of the fourth degree are described for direct imaging and variable lenses with elements having curvatures of the fifth degree, particularly for variation in cubic amplitude. The variable lenses with one or more sliding optical elements referred to in this patent are deemed to comprise all these variants, and all these lenses fall within the concept of "variable lens".

The present invention relates in the first instance to a variable lens, comprising at least two optical elements, wherein at least one of the optical elements is movable in a plane transversely of the optical axis of the lens relative to the at least one remaining element, wherein at least two optical elements have a surface described by a polynomial of at least the third order, and wherein the curvature of the curved surfaces of the optical elements is such that at different relative positions of the displaceable optical elements the resulting lens has a differing strength.

The variable lens with two cubic optical elements is a traditionally important optical component. Both optical elements preferably comprise a surface, a component of which satisfies the basic formula z = Su(x,y)⁼U (axy ²+ bx³/3 ), having added thereto possible corrections for optical aberrations of higher orders. This means that the surfaces are curved according to a third order. This lens consists of two optical elements which slide over each other and which, in different positions, together form a lens of variable optical strength. This principle is developed and described in US-A-3,305,294 for technical applications and for applications in spectacles, but was later also modified for use as focusing lens for analog cameras in US-A-3, 583,790 and US-A-4,650,292. The laterally displacing optical elements are applied here in a fan- like and rotating variation and replace the Waterhouse discs in analog consumer cameras such as the Polaroid Spectra® series. It has however been found that the cubic aberrations of this type of lens in combination with modern digital numerical processing make applications possible for increased depth of field during imaging (US-A-2004,228,005). In addition, properties of this type of variable lens have been recently described for use as medical intraocular lenses in PCT/NL2005/000153 and a non-prepublished Netherlands patent application 1029037 and the international patent application PCT/NL 2006/050050, which also describes several different optical principles and new formulae for variable lenses with sliding optical systems as well as a number of methods for correcting aberrations in such variable lenses.

Instead of surfaces which satisfy the above stated formula, it is also possible to apply optical elements which are each provided with a surface which satisfies the formula z=So(x,y)=O (ex³ + dy³ ' )/3, with Z=So(Xy)= T (ex³ + y³) as basic formula with equal values of c and d, by processing a variation of the above stated basic formula from US- A-3,305,294. In this latter case the direction in which the elements are mutually displaceable will have to extend at an angle of 45° to the x-axis and the y-axis in order to obtain the variable strength. The constants c and d are not necessarily, but preferably equal, so c=d for a correct operation of the variable lens. This also relates to a surface curved according to the third order.

At least one of the two optical elements often has a surface with a component which satisfies a formula for a lens of a fixed strength. An example of such a formula is: z = S_c(x, y) = C(Ja² + Iy²) . This is a formula for a parabolic lens of fixed (dioptric) strength. The surfaces satisfying the first stated formula herein provide for the variability in the strength of the lens formed by the optical elements and, in this case, the parabolic lens provides for an unchangeable basic strength of the lens. The constants k and 1 are not necessarily, but preferably equal, so k=l for a correct operation of the fixed lens. When a lens of a fixed optical strength is placed on only one of the optical elements, the optical axis displaces when the optical elements are displaced.

It should be noted that with a displacement of the optical elements transversely of the optical axis the optical axis thus displaces and the focal length of the lens changes. This effect is new and could for instance be used in optical scanners which could be given a small and extremely thin form. The scanner therefore comprises means for driving in combination with the optical elements.

A following configuration of optical elements provides the measure that the optical x⁴ elements satisfy the basic formula z = S_A (x, y) = A(x²y² H ) . The use of a variable

6 lens with three elements in accordance with the basic formula x⁴ z = S_A(x,y) = A(x²y² H ) with optical elements with curvatures of the fourth order is

6 new.

An embodiment is described here of a variable lens consisting of three optical elements, all functioning for the variation in optical strength, wherein a first optical element has a surface which satisfies the formula

for a fixed optical element, z= for the first moving element and z=

r the second moving element.

The optical strength (inverse focal length) of such a combination is Φ = 4AAx². With correctly chosen functions f(y) and g(y) the combination of the 3 elements can be optimized in accordance with z — S_A (x, y) + f(y)x + g(y) . It is noted that a variable cylindrical lens (°= 2AAy²X² ; focus: Φ = AAAy² ) is created when the elements S₂ and S3 are displaced in a direction (movement: Ay ) transversely of the direction of the variable lens (movement: Ax ). Both sides of an element can of course comprise components of the formulated curvatures. This distribution can provide optical advantages. In this embodiment the moving elements S₂ and S₃ are positioned additionally relative to each other with a fixed element Si in a complementary position relative to Si and S∑. Other embodiments relating to positioning of the elements and their mobility can be envisaged. The factors A_/, h₂ and J1₃ are constants which determine the central thicknesses of the respective optical elements, and the constants e and f are not necessarily, but preferably equal, so e=f for a correct operation of the variable lens, the constants g and h are not necessarily, but preferably equal, so g=h for a correct operation of the variable lens, and the constants i and j are not necessarily, but preferably equal, so i=j for a correct operation of the variable optical lens. A difference in these constants and variation therein can provide optical advantages. Other combinations and values of the constants can cause desired aberrations which can be digitally reconstructed at a later stage for a final image. This embodiment is improved when the optical element Sj is fixed, and when the other elements 6^*2 and S3 are both movable relative to the first element and movable relative to each other. The constants should preferably also be equal, so N=P=A for a correct optical operation of, in this case, a parabolic lens. Two surfaces S2 and S3 are additionally positioned with the third surface Sj complementary to the two said surfaces. It should be noted that in this lens with three elements the lens strength changes quadratically with displacement of the elements. This lens can provide advantages for specific technical applications. The above stated variable lens also has specific variable aberrations which can provide optical advantages. Two of these optical elements of the fourth order can be used to obtain cubic aberrations, to be used for instance for wave front coding. The arrangement with the three elements can however be used as variable optical lens in an optical module. This configuration can also serve as a variable cylindrical lens when the surfaces are displaced in a direction transversely of the direction in which variation in focal length occurs.

A subsequent configuration of optical elements provides the measure that the optical x elements satisfy the basic formula z = S_c(x,y) = C(x²y³ +—) . An embodiment is

described here of a variable lens consisting of three optical elements, also all functioning for the variation in optical strength, but particularly for a variation in cubic amplitude. This cubic component is of great importance for an optical digital module based on wave front coding which can then be digitally reconstructed (decoding) in a final image with large spatial depth of focus (extended depth of field (EDF)).

In this configuration a first optical element has a surface which satisfies the formula

) for a fixed optical element,

z= — ) for the first moving element and

x⁵ z= S₃(x,y)=h₃+R (ox²y³ + p — ) for the second moving element. The amplitude of the resulting cubic component is T = 2CAx². With correctly chosen functions f(y) and g(y) the combination of the three elements can be optimized in accordance with z — S_c (x, y) + f(y)x + giy) ■ It is noted that a phase delay occurs with an amplitude of <_* 6CAy² when the elements S₂ and S₃ are displaced in a direction (movement: Ay ) transversely of the direction of the variation in the cubic component (movement: Ax ) in combination with trefoil aberrations. This effect of a variable phase delay can provide advantages for specific technical applications. Both sides of an element can of course comprise components of the formulated curvatures. This distribution can provide optical advantages. In this embodiment the moving elements SN and Sp are additionally positioned with a fixed element S_F in a complementary position. Other embodiments relating to positioning of the elements and their mobility can be envisaged. The factors hi, h₂ and hi are constants which determine the central thicknesses of the respective optical elements, and the constants k and 1 are preferably, but not necessarily equal, so k=l for a correct operation of the variable lens, the constants m and n are preferably, but not necessarily equal, so m=n for a correct operation of the variable lens and the constants o and p are preferably, but not necessarily equal, so o=p for a correct operation of the variable optical lens. Differences in these constants and variation therein can provide optical advantages. Other combinations and values of the constants can cause desired aberrations which can be digitally reconstructed at a later stage for a final image.

This embodiment is improved when the optical element Si is fixed, and when the other elements S2 and S₃ are both movable relative to the first element and mutually movable. The constants should preferably also be equal, so Q=R=A for a correct operation, although other values for the constants can be envisaged. In this configuration the two surfaces S₂ and S₃ are positioned additionally with the third surface Sj complementary to the two said surfaces. The cubic amplitude changes quadratically relative to a linear displacement, and this can provide technical advantages. This arrangement with the three elements can be used as variable cubic phase mask. The use of the lens described in this patent with three elements and a substantially variable cubic component in x⁵ accordance with the basic formula z - S_c(x,y) — C(x²y³ H ) and optical elements

with curvatures of the fifth order is new. This configuration can also serve as a variable trefoil plate when the elements are displaced in a direction transversely of the direction in which a variation in cubic amplitude occurs.

At least two optical elements, at least one of which is movable, with at least one surface described by z = S_υ(x,y)=U (axy ²+ bx^s/3) and z=S_o(x,y)=O (ex³ + dy³ )/3 , can be used as variable lens for the purpose of changing the focal length and thus bringing the space selectively into focus, and as a variable cubic phase mask. The use as variable cubic phase mask for coding the wave front of such optical elements has already been described in US-A-2004/228,005. The use of these lenses for temporal focus coding, plane selection/swap refocus and foveated focusing is new.

AU the above stated optical elements can of course also be embodied in flat Fresnel designs and via GRIN principles, and be embodied as reflective elements such as mirrors or adaptive mirrors. Modern fast adaptive mirrors are particularly suitable herefor.

In an embodiment of a variable lens for an optical digital module the flexible connecting elements which connect the optical elements comprise a resilient structure. This resilient structure is herein arranged only on one side of the relevant element, and a rigid connection on the other side. The actuation is preferably placed on two sides. An actuation on one side is possible but there occurs a displacement in the focus transversely of the optical axis. This displacement can find specific application, the variable lens could for instance be an element of an optical scanner. A two-sided actuation is however recommended for the application as variable lens with a variable focus on the optical axis. This structure, which is preferably Ω-shaped, is easy to form with a moulding process or machining/cutting operations. This Ω-shaped structure provides the option of embodying these stop means as stop protrusions which are arranged in the Ω-shaped structure and which determine the range of the change in focus.

Another embodiment provides the measure that the actuating means of the variable lens comprise four levers, a first pair of which is connected to a side of one of the optical elements, a second pair of levers is connected to the other side of the optical element, and wherein one of the levers of each pair is connected to a side of an actuating means and both other levers of each pair are connected to a component of the actuating means lying opposite the first point of engagement of the actuating means.

Both the above embodiments are described and illustrated at length in the non- prepublished international patent application PCT7NL 2006/050050 for an application as intra-ocular lens.

Modem techniques and materials provide the possibility of giving the variable lens a thin form. This creates the problem that the lens becomes mechanically limp and the optical surface is deformed by the lateral forces exerted thereon. This will of course result in a deterioration of the optical quality of the lens formed by the optical elements. This is prevented by the measure that the optical elements are provided with strengthening elements which extend on their periphery and whereby they acquire the necessary firmness. Modern fixing techniques provide the option of the strengthening elements being manufactured from a material other than the material from which the optical elements are manufactured. This provides the possibility of choosing a material with optimum properties for both.

All the above stated variable lenses have usual optical symmetrical aberrations. In order to reduce these aberrations as much as possible, the surfaces of one of the optical elements can be provided with a correction surface which satisfies the formula:

for dependent correction of optical deviations with r

R the radius of the curvature of a lens of a fixed optical strength, A the amplitude, x and y the Cartesian transverse coordinates,

the central thickness of the optical element.

z = S(x, y) + a₂ r⁴ + a₂ r⁶ +... + a_n r⁽²ⁿ⁺²⁾

for independent correction of higher-order deviations, including spherical aberrations by a₂ r⁴ or the combination of both methods by ..2 z = S(x,y) + . ^V +a, r⁴ + a₂ r⁶ +... + a,₇ r⁽²"⁺²⁾

R{i+/i-(i+/c)χ(r/R)²}

This approach to corrections of aberrations is known, but application thereof in combination with a variable lens with optical elements of the fourth order as described in this document is new. These corrections can be made on a surface as desired. It should be noted that the corrections for aberrations can be maximized for only a determined position of the optical elements. This position must be carefully chosen so as to optimize the total variable lens quality over the whole range. It is possible here to arrange the correction surface in accordance with the above stated formula on an otherwise flat surface of one of the optical elements, although it is also possible to superimpose the surface in accordance with the above stated correction formula on an optically active surface of one of the optical elements.

The optical elements of all the above stated lens configurations for a variable lens can occupy different variable positions in the Z, X and Y plane independently of each other. As in practically all traditional applications, the main planes of the elements can be in parallel position, they can extend at an angle to each other (wedging), they can together form an angle relative to the optical axis which differs from the traditional perpendicular positioning (tilt) and the spacing between the elements in the direction of the optical axis can be variably adjusted (spacing). Other independent variable positions, such as different forms of rotations of the optical elements, can also be envisaged. Applications of this variable positioning can provide significant optical advantages.

Yet another embodiment provides the measure that the optical surfaces of at least two of the optical elements are the same. It is however also possible to make use of optical elements with mutually differing optical surfaces.

It is also possible to make use of an optical element provided with a surface having a component satisfying a formula for an optical lens of a fixed strength. Technical applications of the variable lenses described here include the following, though not exclusively:

Wave front coding/decoding is one of the optical/digital techniques which can be used to bring about extended depth of field (EDF). The following development makes use of a cubic face mask, produces a per se unfocused intermediate image with full information about the focus of subjects in the space covered. Traditionally a single fixed optical element with the basic form: P(x,y) = α (x^+ y³) with α the parameter determining the degree of extended depth of field or a single fixed element in accordance with S(x,y)=O (xy ²+ x³/3 ) is used as phase mask. The optical transfer function (OTF) and point spread function (PSF) are coded with the phase mask and are in principle not susceptible to defocus. Digital reconstruction of the information in the intermediate image follows, usually with an inverse digitally decoding filter in the form of an LMSE filter. This gives a final image with a considerably greater depth of field compared to an image without coding and reconstruction. For descriptions of wave front coding/decoding technology reference is made to, among others, WO2005054,927, US2005,088,745, AU2003,213,651, WO2004,090,581, US2004, 145,808, US2004,004,766, US2003, 169,944, WO02,057,832, WO0,321,333 and related patents cited therein. A variable phase mask with actuation consisting of variants of the Alvarez and Baker designs of optical elements (US- A-3, 305,294; US-A-4,650,292) with one or two of these optical elements with specific cubic aberrations is described in US-A- 2004,228,005 and the patent literature cited therein. Use is also made here of two sliding optical elements of the fourth order as variable cubic phase mask.

The range of the space which is shown in focus in the final image can be determined precisely with the above variable cubic lens, this in contrast to an arrangement with only a single fixed cubic element. The parameter for the degree of extended depth of field, such as α in the above stated formula for a fixed element and T in the formulae for elements of the fifth order, can hereby be kept as small as possible, this resulting in a greatly improved resolution in the final image. Secondly, a number of measures can be taken specifically to enhance the cubic aberrations of the lens. These measures form the subject-matter of future patents. Applications are in image-processing with visible light, but certainly also light in the infrared frequency range.

Temporal focus coding makes use of an intermediate image formed by an exposure wherein the variable lens passes through a continuous range of focal lengths in relation to the depicted space. Hausler (Optics Communications 6(1) 38-42, 1972) already describes a method of increasing depth of field by displacing a traditional spherical lens along the optical axis during exposure of an image in order to thus produce a uniformly unfocused intermediate image, which image can be digitally reconstructed in a subsequent step into a focused image. Possible variations in the dimensions of the formed image can be either compensated digitally or prevented by additional variable optical systems which pass through the image synchronized with the variable lens. This intermediate image obtained with temporal focus coding is unfocused but does contain all information relating to the focus of the subjects pictured in the space. This image can be converted into a single focused final image with a digital operation. The use of variable lenses with a plurality of sliding optical elements for temporal focus coding is new.

According to yet another preferred embodiment, at least one of the optical elements has a surface with a component satisfying a formula for an optical lens of a fixed strength.

hi addition to a variable lens, the present invention also relates to an optical digital module with a component comprising at least one variable lens as elucidated above and an image recorder, wherein the variable lens is placed in order to project an intermediate image onto the image recorder, and a computer connected to the image recorder and actuating means for optical elements and synchronization means between computer and the variable lens. It is after all precisely when a lens of the above described type is applied in such a camera that the advantages of such a lens, such as an extremely great depth of field, become clearly manifest. Such a lens can in principle also be used in a conventional camera operating with light-sensitive emulsions, but the use of a digital camera provides the option of immediate processing of the signal from the image recorder, which can be attractive in the case of determined exposure methods. According to a more specific preferred embodiment, the optical digital module comprises synchronization means coupled to the image recorder for reading the image recorder and for controlling actuating means of the movable optical elements. The movement of the optical elements can hereby be synchronized with making of the recording, which can take place with a mechanical shutter or, in a camera provided with an image recorder, by reading the image recorder.

In determined exposure methods the intermediate image projected on the image recorder by the optical system is not suitable for direct interpretation. This image is unfocused to the human eye. A processing of the signal representing this intermediate image is then necessary in order to obtain an interpretable image. According to a subsequent embodiment, the computer is adapted for this purpose to process the signal from the image recorder representing the intermediate image projected onto the image recorder into a final signal representing the final image.

When the optical system has the relevant properties, it is then attractive when the numerical digital processor is adapted for reconstruction to a final image of the unfocused intermediate image as the result of at least a cubic optical element.

Yet another preferred embodiment provides the measure that the system is adapted to cause the variable lens to pass through a path through the focal length, and to at least make a recording while passing through this path. The particular advantages of the lens construction according to the invention do after all become manifest during the change in the relative position of the optical elements and the associated change in focal length. It should be noted that the dimensions of the image can change when the focal length of the variable lens changes. These changes can however be corrected by a second variable lens synchronized with the first variable lens, or these changes can be compensated with modifications to the computer.

The module can herein be adapted to make a number of discrete recordings while passing through the path. A single final image of enhanced quality, such as focal depth, can be obtained by electronic processing of the intermediate images obtained during or after making of these recordings. The number of intermediate images for this processing can vary and depends mainly on the nature of the recording and the specifications of the optical digital module.

The computer is therefore preferably adapted to process into a final image a selected number of intermediate images made during the recordings.

It is however also possible for the computer to be adapted to select a final image from the intermediate images made during the recordings (focal plane selection/swap refocus). This intermediate image can then either serve directly as final image or the surface of this intermediate image can once again be depicted with for instance a different setting of the optical digital module for a result with higher resolution of the whole intermediate image or a result which shows only a determined sector of the intermediate image with high optical quality. This method can also be combined with an additional digital temporal focus operation. With a variable lens having two or more sliding optical elements as component of the optical system this can be performed exceptionally quickly and with highly-quality optical results. The use of a variable lens with two or more sliding optical elements for focal plane selection/swap refocus technology is new.

It is further also possible to make the recordings at different intervals. For the distances at which the objects are situated for which there is the greatest interest more recordings can herein be made, and fewer recordings can be made for the other distances. The recording process can hereby be accelerated compared to the situation in which equidistant recordings are made.

It is also possible to adapt the module to make, while passing through the path, a single recording extending over at least a part of the time duration of passing through the path. This single recording can then be read at one time, whereby a composite intermediate image is created which must then be processed in order to obtain a final image. It is also possible to read the intermediate image a number of times, thereby creating an analogy with the above stated situation.

The computer is preferably adapted to process into a final image the at least one intermediate image made during the recording extending over a period of time. Use of the above described variable lenses in an optical digital module for this variation of temporal focus coding is new. It is pointed out here that the above stated variations of the relative position of the displaceable optical elements results in the first instance in a change in the strength or the focal length of the composite lens. This is not however the only effect; the mutual displacement also results in other optical effects. A lens of the above stated type thus has only a limited range in which it projects a focused image. This means that the rest of the image is less focused. The mutual displacement of the optical elements thus provides the possibility of displacing the most focused range of the image to the range for which there is the most interest. Another possibility is formed by making successive recordings while focusing on different areas, and processing the thus obtained intermediate images into a final image which is wholly focused by means of the computer. Such a process is known as foveated focusing.

Foveated focusing produces a preferably wide view, overall image with selected sectors within this image having a higher resolution. Detail can thus be obtained in one or more selected sectors without losing the overview of the overall image. The spherical properties as well as the astigmatic and other aberrations of the variable lens can firstly be used here to form a wide view image. Secondly, in this new application the variable lenses are displaced within the optical system, also deviating from the optical axis, optionally in combination with repositioning of the optical elements of the variable lenses with two or more sliding optical elements relative to each other. Local focus and detail can hereby be obtained. The design of the variable lens can also be fundamentally modified in order to make "foveated focusing" possible. A fixed lens can for instance be additionally arranged on one of the two optical elements, while the other element only provides for the variation in focus and variation in desired aberrations. When the elements are displaced relative to each other, the angle therefore also changes relative to the original optical axis. A repositioning of the optical elements of the variable lenses over different axes relative to each other will perhaps also be necessary in order to achieve a focused result. Optical properties can be modified by placing the optical elements of the variable lens at an angle relative to each other, changing the distance between the elements, rotating the elements, displacing the elements in all possible directions and perhaps positioning the elements to some extent in a spherical contour. Application of a variable lens for foveated focusing and a repositioning of the optical elements of a variable lens which deliberately varies from a parallel positioning of the elements are both new.

It should once again be noted that a synchronization of the variable lens element and the digital processing and possible additional variable lens elements is essential in all of the above, since the position of the optical elements and the associated focal length must be precisely known.

A plurality of optionally synchronized variable lenses can also form part of the construction of a single camera lens. The optical system can consist of one or more variable lenses, optionally in combination with additional optical systems, for instance as part of a triplet, and optionally in combination with a shutter, which can also be realized electronically via the sensor/software combination. The variable optical system can operate at great speeds or via vibration of one or both optical elements or via rotation of a disc having a plurality of optical elements therein. A large number of options are available in the present state of the electromechanical art for the movement of the optical elements and synchronization thereof.

All the above described applications can be embodied with a camera module having only one or a few optionally optically variable optical components, one or more actuators for actuating the variable optical elements, one or more CCD or CMOS sensors optionally in combination with integrated/embedded software for the image processing. Variable lenses can fulfil different functions here, such as for instance a first variable lens for variation in focal length and a second for variable correction of a specific aberration. The design of the combinations depends here of course on the final use of the optical module. This can all be contained in a simple housing and can in principle take both a large and small form. Using present lens production systems this type of camera can be given an exceptionally small form and, with existing silicon- etching lens production, perhaps a micro-scale form. Exceptionally flat and very small variable lenses can be manufactured via Fresnel optical designs, optionally in combination with lithographic etching.

Yet another preferred embodiment provides the measure that at least a part of the housing of the optical digital module is elastically flexible, and this part comprises at least one optical element of a variable lens and actuating means therefor. The housing can hereby position the variable optical elements as well as fulfil a function in the movement of the optical elements.

The optical digital module can also comprise at least one variable optical component which takes a reflective form. Modern, fast, usually piezo-electronically driven adaptive mirrors are particularly suitable for this purpose. The use of these reflective elements depends on the design of the optical digital module and the intended application.

A wholly integrated camera module can be produced by giving the optical part, and at least the part where the variable lens or variable lenses is/are situated, an elastic form and combining it with a simple electromechanical control and actuator or other type of control. The variable lens combinations optional supporting fixed lenses, control and actuating mechanisms and sensor module can be combined to form a camera module in a single injection moulding process.

The above described configuration is of course suitable for light within the spectrum visible to humans. It is however also possible to dimension the device for non- visible light, such as the IR spectrum or UV spectrum.

The present invention will be elucidated hereinbelow on the basis of the accompanying drawings, in which:

Fig. 1 shows a diagram of the components of an optical digital module according to the invention; Fig. 2 shows a cross-sectional view of an embodiment of the optical elements as applied in the construction of figure 1;

Fig. 3 is a view corresponding with figure 2 of a second embodiment;

Fig. 4 is a view corresponding with figure 2 of a third embodiment;

Fig. 5 is a cross-sectional view of the embodiment shown in figure 4, wherein the method of suspension is shown;

Fig. 6 is a cross-sectional view transversely of the optical axis of the embodiment shown in figure 5;

Fig. 7 is a view corresponding with figure 6 of a variant wherein the method of suspension and actuation is modified; and Fig. 8 shows a cross-sectional view of a final embodiment.

Figure 1 shows an optical digital module. The object 1 is depicted via an optical system, in this embodiment a triplet with two fixed lenses and a variable lens which can consist of fixed optical system 2A, 2B and a variable lens, in this example a variable lens of the fifth order with two movable elements 3A, 3B actuated by actuating members 4, wherein the arrows show the direction of actuation. The module also comprises a fixed element 5, an image of which is depicted on a sensor 6, and the thus created signal is transferred to a computer 7 in which a virtual intermediate image 8 is processed into a final image 9 which is shown on an electronic screen or display 10. The computer is also adapted for synchronization and control of the movable optical elements, which signal can be transferred to the actuating means 11. An optional additional variable lens for correction of image dimensions and other additional components are not included in this highly simplified representation.

In this and all subsequent illustrations the optical elements of variable lenses are represented schematically as a triangle, wherein the thickest part of the triangle corresponds to the thickest part of the actual curved optical elements.

Figure 2 shows a variable lens with two optical elements 12A, 12B which are identical, though in mutually reversed position.

Figure 3 shows a variable lens with two optical elements 13, 14, of which one 13 is fixed. This optical element 13 further comprises a fixed lens. The other optical element 14 is movable. This configuration could for instance serve as component of an optical scanner, since as a result of the rest of the system shifting transversely of the optical axis the optical axis 15 shifts, or actually tilts, this being indicated with a broken line 16.

Figure 4 shows a variable lens with three optical elements of the fourth or the fifth order, wherein an optical element 17 is fixed and two optical elements 18A, 18B are placed movably.

Figure 5 shows an embodiment for moving two optical elements 19 and 20 in a variable lens with three elements. In this embodiment both elements can be moved. The movable elements 19, 20 each have a rigid projection 21 on one side and an elastic projection 22 on the other side. A pressure forced or a tensile force, indicated with an arrow 23, displaces both elements 19, 20 over each other.

Figure 6 shows such a construction with a spring construction 24, rigid connections represented by a rectangle 25 and elastic connections represented by circles 26. Protrusions 27 serve here as stop elements defining the extreme relative positions. The point of engagement of the actuating means is indicated with a dot 28. An example is given here in which both optical elements 20, 21 are actuated uniformly from both sides.

Figure 7 shows another embodiment wherein the optical elements 29 and 30 can be displaced via a lever construction with four lever arms 31. Possible points of engagement for an actuating means are indicated with dots 32. Protrusions 33 serve here as stoppers and define the extremes of the variable range.

Figure 8 shows a triple optical module in a flexible housing. Associated lenses 34 are situated here on either side of the flexible lens, which in this embodiment consists of two elements 35 and 36. The actuating means engage at points 37 and 38 which are placed staggered along the central axis. The flexible part of the housing is indicated here with a broken line 39.

Claims

1. Variable lens, comprising at least two optical elements, wherein at least one of the optical elements is movable in a plane transversely of the optical axis of the lens relative to the at least one remaining element, wherein at least two optical elements have a surface described by a polynomial of at least the third order, and wherein the curvature of the curved surfaces of the optical elements is such that at different relative positions of the displaceable optical elements the resulting lens has a differing strength.

2. Variable lens as claimed in claim 1, characterized in that the lens comprises at least one optical element having at least one surface described by

z = S_A(x,y) = A(x²y² +^) . o

3. Variable lens as claimed in claim 2, characterized in that the lens consists of at least three optical elements, with a first element having a surface which is described by

a second element having a surface which is described by z= S₂(x,y)=h₂+N(gx²y²+hx⁴/6) and a third element having a surface which is described by z= S₃(x,y)=h₃-P(ix²y²+jx⁴/6).

4. Variable lens as claimed in claim 1, characterized in that the lens comprises at least one optical element having at least one surface described by

5. Variable lens as claimed in claim 1, characterized in that the lens comprises at least three optical elements, with a first element having a surface which is described by x⁵ z=Si(x,y)=hι-2 C(x²y³ -\ ) , a second element having a surface which is described by

and a third element having a surface which is described by

6. Variable lens as claimed in any of the foregoing claims, characterized in that at least one optical element has a fixed position.

7. Variable lens as claimed in claim 1, characterized in that the lens comprises at least one optical element having at least one surface which is described by

8. Variable lens as claimed in any of the foregoing claims, characterized by at least one element with a surface which is described by:

z = S(x, y) + . ^r + _ai r⁴ + a₂ r⁶ +... + a_n r⁽²"⁺²⁾

R{l + -Jl-(l + k)x(r/R)²}

9. Variable lens as claimed in any of the foregoing claims, characterized in that the optical elements are positioned with their main plane parallel to each other.

10. Variable lens as claimed in any of the foregoing claims, characterized in that the optical surfaces of at least two of the optical elements are the same.

11. Variable lens as claimed in any of the foregoing claims, characterized in that the optical surfaces of each of the optical elements differ.

12. Variable lens as claimed in claim 11, characterized in that at least one of the optical elements has a surface with a component which satisfies a formula for an optical lens of a fixed strength.

13. Variable lens as claimed in any of the foregoing claims, characterized in that the optical elements are designed such that the optical axis of the variable lens is displaced when at least one of the optical elements is displaced in the direction transversely of the optical axis.

14. Optical digital module with a component comprising at least one variable lens as claimed in any of the foregoing claims, characterized by an image recorder, wherein the variable lens is placed in order to project an intermediate image onto the image recorder, and a computer connected to the image recorder and actuating means for optical elements.

15. Optical digital module as claimed in claim 14, characterized by synchronization means coupled to the image recorder for reading the image recorder and for controlling actuating means of the movable optical elements.

16. Optical digital module as claimed in claim 14 or 15, characterized in that the computer is adapted to process the signal from the image recorder representing the intermediate image projected onto the image recorder into a final signal representing the final image.

17. Optical digital system as claimed in claim 14, 15 or 16, characterized in that the numerical digital processor is adapted for reconstruction to a final image of an intermediate image as a result of a variable phase mask.

18. Optical digital module as claimed in any of the claims 14-17, characterized in that the system is adapted so as to cause the variable lens to pass through a path through the focal length, and to at least make a recording while passing through this path.

19. Optical digital module as claimed in claim 18, characterized in that the module is adapted to make a number of discrete recordings while passing through the path.

20. Optical digital module as claimed in claim 19, characterized in that the module is adapted to make recordings at different intervals while passing through the path.

21. Optical digital module as claimed in claim 18, characterized in that the module is adapted to make, while passing through the path, a single recording extending over at least a part of the time duration of passing through the path.

22. Optical digital module as claimed in claim 19 or 20, characterized in that the computer is adapted to process into a final image intermediate images made during a selected number of recordings.

23. Optical digital module as claimed in claim 21, characterized in that the computer is adapted to select a final image from the intermediate images made during the recordings.

24. Optical digital module as claimed in claim 21, characterized in that the computer is adapted to process into a final image the at least one intermediate image made during the recording extending over a period of time.

25. Optical digital module as claimed in claim 20, characterized in that the module is adapted to read the intermediate image projected onto the image recorder repeatedly during making of the recording and that the computer is adapted to process into a final image each read intermediate image in each case.

26. Optical digital module as claimed in any of the claims 14-25, characterized in that the system is adapted to select the associated positioning of optical elements for repeated imaging at a selected focal plane.

27. Optical digital module as claimed in any of the claims 14-26, characterized in that the system is adapted to display selected part-images of the full image, wherein the selected part-image has a greater resolution than the remaining parts of the full image.

28. Optical digital module as claimed in any of the claims 14-27, characterized in that the variable lens is adapted to also occupy positions wherein the optical axis of at least one optical element of the variable lens differs from the optical axis of the rest of the optical digital module.

29. Optical digital camera module as claimed in any of the claims 14-28, characterized in that at least a part of the housing of the optical digital module is elastically flexible and this part comprises at least one optical element of a variable lens and actuating means therefor.

30. Optical digital module as claimed in any of the claims 14-29, characterized in that at least one of the variable optical components comprises at least one optical element with reflective properties.

31. Optical digital module as claimed in any of the claims 14-30, characterized in that the optical digital module is dimensioned for imaging in the infrared frequency range.