Liquid optics zoom lens and imaging apparatus

[0001] This application is related to, and claims the benefit of U.S. Provisional 60/978,338 filed Oct. 8, 2007, the entirety of which is hereby incorporated by reference herein and made a part of the present specification.

[0002] 1. Field of the Invention

[0003] This invention relates to an optical zoom lens system employing liquid optics.

[0004] 2. Description of the Related Art

[0005] Imaging applications have historically used two or more movable zoom lens groups to provide zooming and different focal lengths. An additional lens group for focusing may also be needed.

[0006] However, there are intrinsic disadvantages associated in using zoom and focus lens systems with moving lens groups. In particular, having moving zoom lens groups implies the need for complex mechanically moving parts. Each movable lens group requires support structures and drive mechanics such as cams and motors and in some cases control electronics to facilitate the movements. This system complexity may add size, weight and cost and may make the system operation unreliable over a period of time. These disadvantages together with undesirable limitations, such as a limited range of focal lengths, the inability to focus adequately over the entire focal length range, the inability to focus on close objects, the lack of adequate optical performance over the entire focal length range and focus distance, are present in some previously available zoom lenses having at least two moving zoom lens groups. A mechanically less complex but high performance zoom lens system is needed.

[0007] Zoom lenses use moving lens groups to adjust the magnification of an object as seen at an image. The lens body must be large enough to accommodate the movement of the lens groups. One or more of the moving lens groups may be replaced by a liquid lens cell that has a variable surface shape.

[0008] In one embodiment, a zoom lens system has an axially movable zoom lens group and an axially stationary rear lens group comprising at least one liquid lens cell. In another embodiment, a zoom lens has an axially stationary lens group comprising at least one liquid lens cell and an axially movable rear lens group. The liquid lens cell has first and second contacting liquids, and the contacting optical surface between the contacting liquids has a variable shape. The zoom lens group and the axially stationary lens group are aligned on a common optical axis and arranged to collect radiation emanating from an object space and deliver the radiation to an axially stationary image space as a real image. The zoom lens may also have an axially stationary objective lens group, wherein the objective lens group, the zoom lens group and the axially stationary liquid cell lens group are aligned on a common optical axis. The rear lens group may include an adjustable iris. Axial adjustment of the zoom lens group and variation of the shape between the contacting liquids provide zooming and focusing.

[0009] The shape of the contacting optical surface between the contacting liquids may be controlled electronically. A lookup table may be used in electronically controlling the shape of the contacting optical surface. One index in the lookup table may correspond to a focal setting. Another index in the lookup table may correspond to a zoom setting. Yet another index in the lookup table may correspond to a thermal value. The shape of the contacting optical surface between the contacting liquids and the axial adjustment of the zoom lens group may be controlled together.

[0010] In one embodiment, the zoom lens system comprises a movable lens group and a liquid cell lens group. The movable lens group and liquid cell lens group may be aligned on a common optical axis. The movable lens group and liquid cell lens group are controlled together to achieve zooming and focusing. Zooming may be accomplished by controlling at least one of (i) the liquid cell lens group, (ii) the movable lens group, or (iii) the liquid cell lens group and the movable lens group. Similarly, focusing may be accomplished by controlling at least one of (i) the liquid cell lens group, (ii) the movable lens group, or (iii) the liquid cell lens group and the movable lens group.

[0011] In one embodiment, a camera system comprises a zoom lens having a movable lens group and a liquid cell lens group, and an image capture element positioned at a focus location of the zoom lens system. The image capture element may be an electronic capture device, such as a CCD, or it may be film.

[0012] In one embodiment, a method of zooming a lens includes the steps of moving a lens group along an optical axis and varying the shape of a contact surface in a liquid lens cell group that is aligned along the optical axis. Varying the shape of the contact surface provides focusing.

[0013] In one embodiment, liquid optics allow a zoom focal length range of about 7.5× with object distances from close to infinity. The objective zoom lens system collects radiation from object space and images the radiation at an image plane located just after the lens.

[0014] In one embodiment, an objective zoom lens system employing liquid optics has a focal length zoom region from about 5.9 mm to 45.0 mm. This embodiment was selected as providing a reasonably wide angle lens with a reasonably long focal length, yet maintaining a reasonable diameter lens at a reasonable length. In addition, apertures of F/2.8 to F/4.0 are acceptable for use with charge-coupled device (CCD) and complimentary metal-oxide-semiconductor (CMOS) detectors which have lower light requirements thus higher light sensitivity.

[0015] Benefits include only one movable zoom lens group and one or more liquid lens cells to provide zooming with less mechanical complexity, size and weight. In addition, reliability may improve when used over an extended period of time.

[0016] Axial position adjustment of the zoom lens group and variation of the surface shape between the liquids of one or more liquid lens cells provide zooming. Axial adjustment of the zoom lens group or shape variation in the liquid lens cell (or both), provides focusing and compensation for temperature induced effects such as image defocus and aberration variation which uncompensated may cause image quality degradation.

[0017] It should be understood that the embodiments described herein are for purposes of explaining the invention, and the scope of the invention is not constrained to the described embodiment.

[0023] In the following description of preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention.

[0024] FIG. 1 illustrates a block diagram of a camera 100 with a zoom lens 102. A zoom lens is an assembly of lens elements with the ability to vary focal length. The individual lens elements may be fixed in place, or slide axially along the body of the lens. A lens group may consist of one or more lens elements. The individual lens elements may be constructed from solid-phase materials, such as glass, plastic, crystalline, or semiconductor materials, or they may be constructed using liquid or gaseous materials such as water or oil. At least one movable lens group provides variation of the magnification of an object. As the at least one lens group moves to accomplish magnification, the position of the focal plane may also move. At least one other movable lens group may move to compensate for the movement of the focal plane to maintain a constant focal plane position. Compensation for the movement of the focal plane may also be achieved mechanically by moving the complete lens assembly as the magnification of the lens changes.

[0025] A zoom lens will often have three or more moving lens groups to achieve the zoom and focusing functions. A mechanical cam may link two movable lens groups to perform zooming, and a third movable lens group may be used for focus.

[0026] The zoom range is determined in part by the range of movement for the movable lens elements. Greater zoom ranges require additional space for movement of the lens elements. One or more of the movable lens groups may be replaced by a lens group that implements liquid cell technology. Because liquid cells do not require space for axial movement, the length of the lens design which contains the movable lens groups may be reduced. Alternatively, the space that would have been used for axial movement of the movable lens groups can be used to include additional optical elements. Although a liquid cell does not require space for movement, it may be part of a movable lens group.

[0027] A liquid cell may be used for both zooming and focusing. In one embodiment, a movable lens group is used with a lens group that implements liquid cell technology. There is no need for a mechanical cam with one movable lens group. Not having a cam allows for additional movements.

[0028] One or more movable lens groups are used with one or more liquid cells to achieve zooming and focusing. A single movable lens group and a single liquid cell can perform both zooming and focusing. In one implementation, a zoom system has at least a first and second lens group. The first lens group is relatively high power, and the second lens group is relatively low power, the lens power being equivalent to the inverse of the focal length of the lens. The first lens group comprises conventional glass or other solid lenses and the second lens group comprises at least one liquid lens.

[0029] A liquid cell uses two or more liquids to form a lens. The focal length of the lens is partly determined by the angle of contact between the liquids and the difference in the refractive index of the liquids. The range of power variation is limited by the difference in the refractive index of the liquids employed and the finite range of radius of curvature at the surface interface between the liquids due to space constraints. U.S. Patent Application Publication No. 2006/0126190, herein incorporated by reference, discloses a lens employing the deformation of a drop of liquid through electrowetting.

[0030] Presently contemplated liquid lens systems will have a difference in refractive index of at least about 0.2, preferably at least about 0.3, and in some embodiments at least about 0.4. Water has a refractive index of about 1.3, and adding salt allows varying the refractive index to about 1.48. Suitable optical oils may have a refractive index of at least about 1.5. Even by utilizing liquids with higher, lower or higher and lower refractive indices, for example a higher refractive index oil, the range of power variation remains limited. This limited range of power variation usually provides less magnification change than that of a movable lens group. Therefore, in a simple zoom lens system, to provide zooming while maintaining a constant image plane position most of the magnification change may be provided by one movable lens group and most of the compensation of defocus at the image plane may be provided by one liquid cell. However, it should be noted that more movable lens groups or more liquid cells, or both, may be utilized.

[0031] The movable lens group can have a positive or negative power. The liquid cell can have a range of variable power where the power is always positive, always negative or goes from positive to negative, or vice versa. Proper arrangement of the movable lens group and the liquid cell provides an extended zoom ratio of greater than 2× and preferably greater than 3× while offering good image quality throughout the zoom range. The arrangement, in addition to zooming, may also provide focusing at different object distances over an extended focus range by utilizing additional available power variation from the liquid cell, the movable lens group or both. This additional power variation provided by the liquid cell or the movable lens group or both for focusing is readily available. Since one movable lens group does not necessarily require a cam with a fixed locus of movement, the position of the movable zoom lens group can be adjusted for zooming and focusing. High performance imaging is achieved by utilizing both the movable zoom lens group and the liquid cell for zooming and focusing.

[0032] It is also possible to replace the movable zoom lens group with at least one liquid cell. This would increase the complexity of the optical system and may cause the optical system to have other disadvantages, such as reduced light transmission.

[0033] FIG. 1 also illustrates a lens control module 104 that controls the movement and operation of the lens groups in lens 102. The control module 104 includes electronic circuitry that controls the radius of curvature in the liquid lens cell. Electronic circuitry may also control the position of the movable lens group. The appropriate electronic signal levels for various focus positions and zoom positions can be determined in advance and placed in a lookup table. Alternatively, analog circuitry or a combination of circuitry and a lookup table can generate the appropriate signal levels. In one embodiment, a polynomial is used to determine the appropriate electronic signal levels. Points along the polynomial could be stored in a lookup table or the polynomial could be implemented with circuitry.

[0034] Thermal effects may also be considered in the control of the radius of curvature of surface 21 or the position of movable lens group G2 or both. The polynomial or lookup table may include an additional variable related to the thermal effects.

[0035] The control module 104 may include preset controls for specific zoom settings or focal lengths. These settings may be stored by the user or camera manufacturer.

[0036] FIG. 1 further illustrates an image capture module 106 that receives an optical image corresponding to an external object. The image is transmitted along an optical axis through the lens 102 to the image capture module 106. The image capture module 106 may use a variety of formats, such as film (e.g., film stock or still picture film), or electronic image detection technology (e.g., a CCD array or video pickup circuit). The optical axis may be linear, or it may include folds.

[0037] Image storage module 108 maintains the captured image in, for example, on-board memory or on film or tape. In one embodiment, the storage medium is removable (e.g., flash memory, film canister, or tape cartridge).

[0038] Image transfer module 110 provides transferring of the captured image to other devices. For example, the image transfer module 110 may use one or a variety of connections such as a USB port, IEEE 1394 multimedia connection, Ethernet port, Bluetooth wireless connection, IEEE 802.11 wireless connection, video component connection, or S-Video connection.

[0039] The camera 100 may be implemented in a variety of ways, such as a video camera, a cell phone camera, a digital photographic camera, or a film camera.

[0040] An embodiment of a zoom lens will now be described by way of a design example. Referring first to FIG. 2, each lens element is identified by the letter “E” followed by a numeral from 1 through 20 and the general configuration of each lens element is depicted, but the actual radius of each lens surface is set forth below in TABLE 1. The lens, object, stop or iris and image surfaces are identified by a numeral from 1 through 36. The three lens groups are identified in FIG. 2 by the letter “G” followed by a numeral from 1 through 3 and the liquid lens cell is identified by the letters “LC” and comprises optical surfaces 19 through 23. The optical axis is identified in FIG. 2 by a numeral 50.

[0041] Each lens element has its opposite surfaces identified by a separate but consecutive surface number as, for example, lens element E1 has lens surfaces 2 and 3, lens element E9 has lens surfaces 17 and 18 and so forth, as shown in FIG. 2. The location of the object to be imaged, particularly as it relates to focus distance, is identified by a vertical line and the numeral 1 on the optical axis 50 and the real image surface is identified by the numeral 36. All of the lens surfaces are spherical or plano except lens surfaces 4 and 8 which are aspheric surfaces that are non-spherical, non-plano but rotationally symmetrical about the optical axis.

[0042] Before describing the detailed characteristics of the lens elements, a broad description of the lens groups and their axial positions and movement, and, the liquid lens cell and the variation in surface shape of contacting liquids will be given for the zoom lens system 60.

[0043] The positive or negative power of each lens group is defined as the inverse of the focal length. The resultant optical power of each group of lenses is as follows: the objective lens group G1 is positive, the zoom lens group G2 is negative and the rear lens group G3 is positive, from a lower positive value to a higher positive value as the shape of the surface in the liquid cell is varied. The horizontal arrow with arrowheads on both ends in the upper portion of FIG. 2 indicates that the zoom lens group G2 is movable in both axial directions.

[0044] While only the lens elements are physically shown in FIG. 2, it is to be understood that mechanical devices and mechanisms are provided for supporting the lens elements and for causing axial movement of the movable zoom lens group in a lens housing or barrel. In addition, it is to be understood that electronic circuitry changes the profile of the variably shaped optical surface in the liquid lens cell.

[0045] The lens construction and fabrication data for the above described zoom lens system 60 is set forth below in TABLE 1. The data in TABLE 1 is given at a temperature of 25° C. (77° F.) and standard atmospheric pressure (760 mm Hg). Throughout this specification measurements are in millimeters (mm) with the exception of wavelengths which are in nanometers (nm). In TABLE 1, the first column “Item” identifies each optical element and each location, i.e. object plane, image plane, etc., with the same numeral or label as used in FIG. 2. The second column identifies the “Group” to which that optical element (lens) belongs with the same numerals used in FIG. 2. The third column “Surface” is a list of the surface numbers of the object (line “1” in FIG. 2 and “Object” in TABLE 1), the Stop (iris) 13 and each of the actual surfaces of the lenses, as identified in FIG. 2. The fourth column “Focus Position” identifies three typical focus positions (F1, F2 and F3) for the zoom lens system 60 wherein there are changes in the distance (separation) between some of the surfaces listed in the third column and there are changes in the radius of curvature of the surface 21 listed in the third column, as described below more thoroughly. The fifth column “Separation” is the axial distance between that surface (third column) and the next surface. For example, the distance between surface S2 and surface S3 is 1.725 mm.

[0046] The sixth column, headed by the legend “Radius of Curvature,” is a list of the optical surface radius of curvature for each surface, with a minus sign (−) meaning the center of the radius of curvature is to the left of the surface, as viewed in FIG. 2 and “Infinity” meaning an optically flat surface. The asterisk (*) for surfaces 4 and 8 indicate these are aspheric surfaces for which the “radius of curvature” is a base radius. Use of aspherical surfaces provides for the correction of aberrations in the zoom lens while enabling a smaller overall size and a simpler configuration. The formula and coefficients for the surface profiles of aspheric surfaces 4 and 8 are governed by the following equation:

[0047] $z=\frac{{\mathrm{cy}}^2}{1+{\left[1-\left(1+\kappa \right)c^2{y}^2\right]}^{1/2}}+{\mathrm{Ay}}^4+{\mathrm{By}}^6+{\mathrm{Cy}}^8+{\mathrm{Dy}}^{10}+{\mathrm{Ey}}^{12}+{\mathrm{Fy}}^{14}$

[0048] where:

[0049] c=surface curvature (c=l/r where r is the radius of curvature)

[0050] y=radial aperture height of surface measured from the X and Y axis, where:
y=(X²+Y²)^1/2

[0051] κ=conic coefficient

[0052] A, B, C, D, E, F=4^th, 6^th, 8^th, 10^th, 12^th and 14^th, respectively, order deformation coefficients

[0053] z=position of a surface profile for a given y value or measured along the optical axis from the pole (i.e., axial vertex) of the surface

The coefficients for surface 4 are:
κ=−0.6372
A=0.9038×10⁻⁶
B=0.2657×10⁻⁸
C=−0.1105×10⁻¹
D=+0.4301×10⁻¹³
E=−0.8236×10⁻¹⁶
F=0.6368×10⁻¹⁹
The coefficients for surface 8 are:
κ=0.0000
A=0.5886×10⁻⁴
B=−0.5899×10⁻⁶
C=0.8635×10⁻⁸
D=−0.5189×10⁻¹⁰
E=−0.1186×10⁻¹¹
F=0.1631×10⁻¹³

[0054] Columns seven through nine of TABLE 1 relate to the “Material” between that surface (third column) and the next surface to the right in FIG. 2, with the column “Type” indicating whether there is a lens (Glass) or empty space (Air) or liquid lens (Liquid) between those two surfaces. The glass and liquid lenses are identified by optical glass in the column “Code”. For convenience, all of the lens glass has been selected from glass available from Ohara Corporation and the column “Name” lists the Ohara identification for each glass type, but it is to be understood that any equivalent, similar or adequate glass may be used. Also, the lens liquid of oil has been selected from a liquid available from Cargille Laboratories, Inc., and water is commonly available from various sources, but it is to be understood that any equivalent, similar or adequate liquid may be used. The water liquid at surface 20 has the following refractive indices 1.331152, 1.332987, 1.334468 and 1.337129 at respective wavelengths 656.27, 589.29, 546.07 and 486.13 nanometers. The oil liquid at surface 21 has the following refractive indices 1.511501, 1.515000, 1.518002 and 1.523796 at respective wavelengths 656.27, 589.29, 546.07 and 486.13 nanometers.

[0055] The last column of TABLE 1 headed “Aperture Diameter” provides the maximum diameter for each surface through which the light rays pass. All of the maximum aperture diameters, except for the Stop surface 13, are given at a wavelength of 546.1 nanometers for a maximum image diameter of about 6 mm and F-numbers of F/2.8 to F/4.0 at the Image Plane, for all Zoom and Focus Positions. The maximum aperture diameter of the Stop surface 13 is given in TABLE 1 at a wavelength of 546.1 nanometers and an F-number of F/2.8 at the Image Plane for Zoom Position Z1 and Focus Position F1. At the Image Plane 36, the Maximum Aperture Diameter is given as an approximate value.

[0056]

TABLE 1
Optical Prescription
	Focus		Radius of	Material	Aperture
Item	Group	Surface	Position	Separation	Curvature (mm)	Type	Name	Code	Diameter (mm)
Object		1	F1	Infinity	Infinity	Air
			F2	1016.2500
			F3	378.7500
E1	G1	2	All	1.7250	59.1716	Glass	SLAM66	801350	37.161
		3	All	0.0750	34.5954	Air			35.567
E2	G1	4	All	6.7565	*33.0488	Glass	SFPL51	497816	35.618
		5	All	0.0750	2758.9929	Air			35.182
E3	G1	6	All	5.8657	32.7151	Glass	SFPL53	439950	33.680
		7	F1	TABLE 2	−2981.4301	Air			33.034
			F2	TABLE 2
			F3	TABLE 2
E4	G2	8	All	0.7652	*461.6464	Glass	SLAH64	788474	14.273
		9	All	3.8333	8.3339	Air			11.605
E5	G2	10	All	2.6582	−12.6370	Glass	SFPL53	439950	11.587
E6	G2	11	All	3.2165	18.1883	Glass	SLAM66	801350	12.383
		12	F1	TABLE 3	−55.4718	Air			12.337
			F2	TABLE 3
			F3	TABLE 3
Stop/	G3	13	All	0.6371	Infinity				6.708
Iris
E7	G3	14	All	5.7168	−26.3844	Glass	SLAH65	804466	6.757
E8	G3	15	All	2.6250	9.3177	Glass	STIH53	847238	8.304
		16	All	0.8432	−16.3366	Air			8.533
E9	G3	17	All	2.5647	−9.2859	Glass	SLAH58	883408	8.508
		18	All	2.2767	−11.1961	Air			9.665
E10	G3	19	All	0.4500	Infinity	Glass	SBSL7	516641	10.151
E11	G3	20	All	1.5000	Infinity	Liquid	WATER		10.201
E12	G3	21	F1	1.5000	TABLE 4	Liquid	OIL	T300	10.367
								04091-
								AB
			F2		TABLE 4
			F3		TABLE 4
E13	G3	22	All	0.4500	Infinity	Glass	SBSL7	516641	10.584
		23	All	0.0750	Infinity	Air			10.642
E14	G3	24	All	3.1583	120.2680	Glass	SLAH65	804466	10.680
E15	G3	25	All	0.6000	−7.2241	Glass	STIH10	728285	10.724
		26	All	0.0750	13.8153	Air			10.634
E16	G3	27	All	3.0844	13.7118	Glass	SBSM10	623570	10.696
		28	All	0.3424	−11.1618	Air			10.713
E17	G3	29	All	0.6000	−9.5071	Glass	STIH13	741278	10.652
		30	All	0.0750	68.8748	Air			11.180
E18	G3	31	All	1.7063	18.2078	Glass	SLAL13	694532	11.589
		32	All	26.6908	−115.6915	Air			11.592
E19	G3	33	All	3.1085	10.2784	Glass	SNPH1	808228	9.888
E20	G3	34	All	2.7193	−9.9003	Glass	SLAH58	883408	9.581
		35	All	2.6192	58.0014	Air			7.805
Image		36	All	0.0000	Infinity	Air			6.008

[0057] Zoom lens system 60 is provided with an optical stop at the surface 13 which controls the diameter of the aperture through which light rays may pass at that point. The optical stop is the location at which a physical iris is located. The iris is located before the rear lens group G3 and is axially stationary with that lens group. Note that in FIG. 4A, the rim rays pass through the axis side of the tic marks of the optical stop surface 13 such that the zoom lens system has no vignetting of light beams at any field position, zoom position and focus position. However, note that the F-number varies through zoom and focus positions and the iris opens or closes accordingly. The diameter of the iris at zoom positions Z1-Z8 for focus position F1 is 6.71, 6.39, 5.96, 5.53, 5.18, 4.84, 4.63 and 4.61. This shows that the iris located at 13 should close as the focal length increases. As compared to focus position F1, the diameter of the iris at zoom positions Z1-Z8 for focus positions F2 and F3 changes by a small amount of less than 0.3 mm diameter to maintain the same F-numbers as for focus position F1.

[0058] Referring to TABLE 1, for illustrating the scope and versatility of the design there are eight different Zoom Positions Z1, Z2, Z3, Z4, Z5, Z6, Z7 and Z8 and three different Focus Positions F1, F2 and F3 set forth in the data which, in effect, provides specific data for twenty four (3×8=24) different combinations of positions for the movable zoom lens group G2 and the variable shape optical surface 21.

[0059] The focal lengths of zoom lens system 60 for zoom positions Z1-Z8 at focus position F1, at a wavelength of 546.1 nanometers are; 5.89, 7.50, 11.25, 15.00, 18.75, 30.00, 41.25 and 45.00 mm, respectively. The corresponding F-numbers for the focal lengths for data positions Z1-Z8, at a wavelength of 546.1 nanometers are; 2.80, 2.90, 3.05, 3.25, 3.45, 3.70, 3.95 and 4.00, respectively.

[0060] For Focus Position F1 the Object Plane 1 is assumed to be at infinity, for F2 the Object Plane 1 is at an intermediate distance of about 1016.25 mm, and for F3 the Object Plane 1 is at a close distance of about 378.75 mm (i.e., 378.75 mm away from the image plane). At each of these three Focus Positions F1, F2 and F3, the lens groups G1 and G3 remain in the same position throughout the full range of movement of the zoom lens group G2. TABLES 2 and 3 provide separation values of surfaces 7 and 12 and TABLE 4 provides the radii of curvature of surface 21 for zoom positions Z1-Z8 and F1-F3.

[0061]

TABLE 2
Surface	Focus	Z1	Z2	Z3	Z4	Z5	Z6	Z7	Z8
7	F1	0.0832	5.7132	13.7126	18.4633	21.6974	27.4007	30.5400	31.3096
7	F2	0.0902	5.7486	13.6468	18.3289	21.5154	27.0776	30.0174	30.7361
7	F3	0.0750	5.6942	13.4674	18.1217	21.3355	26.7467	29.5798	30.2701

[0062]

TABLE 3
Surface	Focus	Z1	Z2	Z3	Z4	Z5	Z6	Z7	Z8
12	F1	31.5294	25.8992	17.8996	13.1486	9.9140	4.2101	1.0701	0.3000
12	F2	31.5178	25.8581	17.9590	13.2762	10.0892	4.5268	1.5870	0.8729
12	F3	31.5324	25.9120	18.1380	13.4831	10.2689	4.8577	2.0248	1.3384

[0063]

TABLE 4
Surface	Focus	Z1	Z2	Z3	Z4	Z5	Z6	Z7	Z8
21	F1	−33.9902	−40.9700	−60.9667	−84.8892	−106.7630	−101.7297	−58.3998	−48.6792
21	F2	−34.3890	−42.0587	−65.5384	−101.1799	−154.9184	−370.2777	−263.5374	−212.3139
21	F3	−35.0134	−43.6001	−72.6330	−133.7178	−351.2333	214.4454	125.5481	115.8049

[0064] Of course, it will be understood that continuous focusing is available between the extreme Focus Positions F1 and F3, that continuous zooming is available between the extreme Zoom Positions Z1 and Z8, and that any combination of continuous focusing and zooming is available within the described focus and zoom ranges with the lens system 60.

[0065] The zoom lens system 60 shown in FIG. 2 and prescribed in TABLE 1 has focal lengths for lens groups G1 and G2 of 54.30 and −12.25 mm respectively. Also, lens group G3, due to the variable shape of the optical surface 21 between the liquids, has a variable focal length which has a minimum value of +30.18 mm and a maximum value of +38.97 mm at zoom position Z1 and focus position F1, and, zoom position Z8 and focus position F3 respectively. The liquid cell LC of zoom lens system 60 is shown in FIGS. 3A and 3B, demonstrating the two extreme radii of curvature from TABLE 1 of the variable shape optical surface 21 between the liquids. In FIGS. 3A and 3B the two radii of curvature of surface 21 are −33.99 and +115.80 mm respectively. The two extreme focal lengths of the liquid cell LC, in FIGS. 3A and 3B, are −185.20 and 630.97 mm respectively. This difference happens at zoom position Z1 and focus position F1, and, zoom position Z8 and focus position F3. In this embodiment the volume of the two liquids between surfaces 20, 21 and 21, 22 varies as the shape of the variable surface changes. However, it is also possible to maintain a constant volume for each liquid by applying small, equal but opposite, changes to the axial separation between surfaces 20, 21 and 21, 22.

[0066] Referring now to FIGS. 4A, 4B, and 4C, the zoom lens system 60 is shown with the zoom lens group in various positions, the shape of the variable surface in the liquid cell in various positions and with light ray traces for those positions. FIG. 4A represents the focus position F1 and zoom position Z1 for which data is set forth above in TABLE 1 with infinity focus and a small focal length of about 5.9 mm. FIG. 4B represents the focus position F2 and zoom position Z3 from TABLE 1 with an intermediate focus and a focal length of about 11.3 mm. FIG. 4C represents the focus position F3 and zoom position Z8 from TABLE 1 with close focus and a focal length of about 44.8 mm.

[0067] FIGS. 4A, 4B and 4C show three axial locations of the zoom lens group G2 with corresponding three surface shapes for the variable optical surface 21 for the respective zoom and focus positions; Z1, F1 and Z3, F2 and Z8, F3.

[0068] The optical performance of zoom lens system 60 is give in FIGS. 5A, 5B and 5C wherein the diffraction based polychromatic modulation transfer function (“MTF”) data (modulation versus spatial frequency) is shown in percent (%) for five different Field Positions in three different combinations of the zoom and focus positions set forth in TABLE 1, namely Z1, F1, Z3, F2 and Z8, F3 which are representative examples. The Field Positions are set forth in two values, both the normalized image height (mm) and the actual object space angle (degree) from the optical axis. The MTF percentages are at the wavelengths and weightings set forth in the top right-hand corner of FIGS. 5A, 5B and 5C and are graphically shown for tangential (T) and radial (R) directions of measurement at the image plane 36. Note that the tangential and radial values are equal at the axial field position (AXIS) and are depicted with only one plot. The maximum spatial frequency shown is 90 cycles/mm which given the image diameter of about 6 mm and choice of detector pixel size may provide high quality images at least up to high definition television (HDTV) resolution, namely 1920 pixels horizontally by 1080 pixels vertically. MTF at a spatial frequency is a relatively standard measurement of optical performance, wherein the value “90 cycles/mm” means 90 pairs of black and white lines per millimeter on a chart from which the clarity is determined. The highest MTF value is about 89% at the full radial field for zoom position Z1 and focus position F2. The lowest MTF value is about 58% at the full tangential field for zoom position Z2 and focus position F3. The minimum relative illumination is about 75% at zoom position Z1 and focus position F1. In general, higher relative illumination values are better, because a low number means that light is falling off in the corners of the picture. High full field relative illumination is preferred for state of the art detectors, which have a constant response to light in all areas and will faithfully reproduce shading in the corners of the image along with changes to the image during zooming. Illumination less than 50% may result in shading in an electronic detector, but will likely be acceptable for film. The highest positive distortion is +3.04% at zoom position Z3 and focus position F1 and the lowest negative distortion is −2.98% at zoom position Z1 and focus position F3. The so-called “breathing” problem of lenses in general (but which may be more prevalent in zoom lenses) wherein the image changes size from long to short focus is virtually absent in zoom lens system 60 at the short focal length of the zoom range where it is most noticeable due to the large depth of field. The lowest breathing is −0.2% at zoom position Z1 and focus position F3 and the highest breathing is −19.5% at zoom position Z8 and focus position F3. Note that at infinity focus (F1), breathing is zero because that is the reference field of view.

[0069] All of the performance data is given at a temperature of 25° C. (77° F.), standard atmospheric pressure (760 mm Hg), and at the full apertures available in the zoom lens system 60. However, the zoom lens system 60 does provide substantially constant performance, as for example the MTF values, over a temperature range of 0° to 40° C. (32° to 104° F.) and, if a small degradation in performance (MTF) is acceptable, the operable temperature range can be extended to −10° to 50° C. (14° to 122° F.) or more. For a change in temperature the optimum performance may be achieved by further axial adjustment of the zoom lens group G2 or further change of shape of the contacting optical surface 21 or a combination of both together. This may happen at all zoom and focus positions. At low temperatures of about 0° C. (32° F.) or below, to avoid freezing (forming a solid), the liquids may need to be heated or be replaced with doped liquids in a similar way to anti-freeze being added to water in a car radiator for low temperature operation. However, note that these material temperature changes preferably should not significantly change the optical characteristics of the liquids.

[0070] While the described embodiment using zoom lens system 60 is of the appropriate dimensions for use with a 6 mm diameter (so called third inch chip sensor), the dimensions of this zoom lens system may be appropriately scaled up or down for use with various film and electronic detector image formats.

[0071] Among the many advantages of the zoom lens system 60 is that of providing zooming over a wide range of focal lengths utilizing only one axially moving zoom lens group. The design of the zoom lens system 60 creates a high performance and mechanically less complex lens system than most conventional high performance zoom lens systems which require at least two axially movable zoom lens groups and corresponding mechanics. The unique lens design of the zoom lens system 60 provides focusing over a large region of focus distance without additional movable lens groups and corresponding mechanics. The disclosed design of zoom lens system 60 is exemplary, and other designs will fall with the scope of the invention. Other features and advantages of the zoom lens system 60 will appear to those skilled in the art from the foregoing description and the accompanying drawings.

[0072] It is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the invention as defined by the appended claims.