Patent ID: 12204087

DETAILED DESCRIPTION

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details set forth in the following description or exemplified by the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

The terms “comprises”, “comprising”, “includes”, “including”, and “having” together with their conjugates mean “including but not limited to”.

The term “consisting of” has the same meaning as “including and limited to”.

The term “consisting essentially of” means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a compound” or “at least one compound” may include a plurality of compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

In discussion of the various figures described herein below, like numbers refer to like parts. In some cases, pluralities of similar or identical elements are marked with same numbers followed by letters, in some cases; same number without the letter refers to any of these elements. The drawings are generally not to scale. For clarity, non-essential elements were omitted from some of the drawing.

The optical setup for endoscopes typically used in the prior art requires a relatively large overall optical length (total optical track) of the entire optical system, which is disadvantageous for endoscopes, in particular those used as colonoscopes and gastroscopes, particularly if used in endoscopes having side-viewing camera or cameras, such as endoscopes according to embodiments of the present invention.

In addition, in sensors (such as CCD sensors) used in endoscopes of the prior art, the pixels are partially covered by a photo-shielding film, so that the light energy is concentrated in the center of the pixel, where there is a “window” in the photo-shielding film. This improves the signal-to-noise ratio and increases the light utilization efficiency. However, this also causes the sensor to be sensitive to incident angles between the light rays which have passed the micro-lenses of the sensor and the optical axis of the system. Thus, light rays having relatively small incident angles may reach the pixel, while light rays having relatively large incident angles (between the light rays which have passed the micro-lenses of the sensor and the optical axis of the system) may not reach the “window” and thus the pixel, leading to significant energy losses. The losses are maximized at the edges of the field of view, i.e. for light rays having incident angles close to that of the chief ray.

There is thus provided herein, according to some embodiments, a lens system (assembly) configured for use in an endoscope, such as colonoscope, particularly for use in a multi-sensor endoscope/colonoscope. The lens system, (optionally together with the sensor) according to some embodiments of the invention, has a short total optical length (track), for example, 5 mm or less. The lens system, according to some embodiments of the invention, is configured to provide a large incident angle, for example, a chief incident angle (for example the incident angles forming by rays R6inFIGS.4a-4c) larger than 20°, larger than 25°, larger than 30° or between about 20-40°. The lens system, according to some embodiments of the invention provides minimal distortion (for example, less than 80%).

According to some embodiments, the sensor which is used together with the lens system, is configured to have a window in the photo-shielding film configured to allow rays having large incident angle (for example, a chief incident angle larger than 20°, larger than 25°, larger than 30° or between about) 20-40° to reach the pixel and thus improve the distortion. According to some embodiments, the width of the window (or any other dimensional parameter) may be about 30-60% of the width of the corresponding pixel. According to some embodiments, the micro-lenses of the sensor may be configured to provide substantially aplanatic conditions. In other words, the sensor may be configured to provide an image substantially free of aberrations.

FIG.1aschematically depicts an external isometric view of an endoscope (for example, a colonoscope)200having multiple fields of view according to an exemplary embodiment of the current invention.

According to an exemplary embodiment of the current invention, head230of endoscope200comprises at least a forwards looking camera (such as a TV camera) and at least one side looking camera (such as a TV camera).

FIG.1ashows front camera element236of forwards looking camera116(seen inFIG.2c) on the front face320of head230. The term “camera element” may generally refer to a camera and the optical system/assembly related to the camera. Optical axis of forwards looking camera116(seen for example inFIG.2a) is substantially directed along the long dimension of the endoscope. However, since forwards looking camera116is typically a wide angle camera, its Field of View (FOV) may include viewing directions at large angles to its optical axis. Additionally, optical windows242aand242bof discrete light sources such as Light Emitting Diodes (LEDs)240aand240bare also seen on front face320of head230. It should be noted that number of LEDs used for illumination of the FOV may vary. Distal opening340of working channel262(seen for example inFIG.2d) may preferably be located on front face320of head230, such that a surgical tool inserted through working channel262and deployed beyond front face320may be viewed by forwards looking camera116.

Distal opening344of a fluid channel may preferably also be located on front face320of head230. The fluid channel leading to distal opening344may be used as a jet channel for cleaning the colon.

Liquid injector346having a nozzle348aimed at front camera element236is used for injecting fluid to wash contaminants such as blood, feces and other debris from front camera element236of forwards looking camera. Optionally the same injector is used for cleaning both front camera element236and one or both optical windows242aand242b. Injector346may receive fluid (for example, water and/or gas) from the fluid channel or may be fed by a dedicated cleaning fluid channel.

Visible on the side wall362of head230is the front camera element256of side looking camera220(two such cameras are seen inFIG.2a) and optical window252of a discrete light sources such as LED250. It is noted that the number of the discrete light sources may vary. Optical axis of side looking camera220may be substantially directed perpendicular to the long dimension of the endoscope. However, since side looking camera220is typically a wide angle camera, its field of view may include viewing directions at large angles to its optical axis.

Liquid injector366having a nozzle368aimed at front looking camera element256is used for injecting fluid to wash contaminants such as blood, feces and other debris from front camera element256of side looking camera. Optionally the same injector is used for cleaning both front camera element256and optical windows252. Preferably, injectors346and366are fed from same channel. An optional groove370helps directing the cleaning fluid from nozzle368towards front camera element256. Groove370may be beneficial when side wall362is near or pressed against the rectal wall. Optionally, injector366may be at least partially recessed in groove370, thus reducing the maximum diameter of head230and reduce the risk of injury to the rectal wall due to friction with injector366.

In the depicted embodiment, flexible shaft260is constructed of a plurality of links382connected to each other by pivots384. Links382allows pushing, pulling and rotating the endoscope while pivots384provide limited flexibility. The shaft is preferably covered with an elastic sheath (removed for clarity in this figure). The lumen in links382holds the working channel262. Not seen in this figure are the fluid channel connected to opening344, optional cleaning fluid channel and electrical cables supplying power to the LEDs and cameras and transmitting video signals from the camera. Generally, the shaft may also comprise mechanical actuators (not seen), for example cables attached to the links for directing and aiming the head during use.

It should be noted that while only one side looking camera is seen inFIG.1a, optionally, according to some embodiments, two or more side looking cameras may be located within head230. When two side looking cameras are used, the side looking cameras are preferably installed such that their field of views are substantially opposing. According to some embodiments, Different configurations and number of side looking cameras are possible and covered within the general scope of the current invention.

FIG.1bschematically depicts a front view of head230of endoscope200having multiple fields of view according to an exemplary embodiment of the current invention.

According to an exemplary embodiment of the current invention, head230of endoscope200comprises at least a forwards looking camera and at least one side looking camera.FIG.2bshows a front camera element236of forwards looking camera116on the front face320of head230. Additionally, optical windows242aand242bof LEDs240aand240bare also seen on front face320of head230. Distal opening340of working channel and distal opening344of a fluid channel are preferably also located on front face320of head230. Liquid injector346having a nozzle348is also visible in this view.

Additionally, Liquid injectors366aand366baimed at side looking camera element256aand256brespectively are used for injecting fluid to wash contaminants such as blood, feces and other debris from front camera element256of side looking cameras.

FIG.1cschematically depicts a side view of endoscope200having multiple fields of view according to an exemplary embodiment of the current invention.

FIG.1cshows front camera element256of side looking camera220, groove370and optical window252on the side wall362of head230. Liquid injectors346and366are also visible in this view.

FIG.2aschematically depicts a cutout isometric view of an endoscope400having multiple fields of view according to another exemplary embodiment of the current invention.

According to an exemplary embodiment of the current invention, head230of endoscope200comprises at least a forwards looking camera116and two side looking cameras220aand220b.

Optical windows242aand242bof LEDs used for forward illumination are also seen on front face of head230.

Distal opening340of working channel is preferably located on front face of head230such that a surgical tool inserted through the working channel262and deployed beyond front face may be viewed by forwards looking camera116.

Distal opening344of a fluid channel is preferably also located on front face of head230. The fluid channel leading to distal opening344may be used as a jet channel for cleaning the colon.

Liquid injector346having a nozzle aimed at front camera element of camera116is used for injecting fluid to wash contaminants such as blood, feces and other debris from front camera element of forwards looking camera116. Optionally the same injector is used for cleaning the front camera element and one or both optical windows242aand242b. Injector346may receive fluid from the fluid channel or may be fed by a dedicated cleaning fluid channel.

Visible on right hand side of head230is the front camera element256bof side looking camera220band optical window252bof side illuminating LED.

Liquid injector366bhaving a nozzle aimed at front camera element256bis used for injecting fluid to wash contaminants such as blood, feces and other debris from front camera element256bof side looking camera220b. Optionally the same injector is used for cleaning both front camera element256band optical windows252b. An optional groove370bhelps directing the cleaning jet from injector366btowards front camera element256b.

Although not seen in this figure, it is understood that equivalent elements366a,370a,256aand252aare present on the left hand side of head230.

Preferably, all the injectors346and366are fed from same channel.

In the depicted embodiment, flexible shaft260is constructed of a plurality of links382(only one is marked for clarity). Electrical cable396within shaft260is seen connected to cameras116,220aand220b. The same or separate electrical cable is used to power the LEDs.

FIG.2bschematically depicts a cross section of an endoscope200having multiple fields of view showing some details of the head230according to an exemplary embodiment of the current invention.

According to the current invention, head230of endoscope200comprises at least a forwards looking camera116and two side looking cameras220aand220b. Each of cameras116and220is provided with an optical imaging system such as lens assemblies (systems)132and232respectively and solid state detector arrays134and234respectively. Front camera elements236and256of cameras116and220respectively may be a flat protective window, but optionally an optical element used as part of the imaging systems such as solid state detector arrays134and234respectively. Optionally, cameras116and220are similar or identical, however different camera designs may be used, for example, field of views118and218may be different. Additionally or alternatively, other camera parameters such as: resolution, light sensitivity, pixel size and pixel number, focal length, focal distance and depth of field may be selected to be same or different.

Light is provided by Light Emitting Diodes (LED) that illuminates the field of views. According to some embodiments, white light LEDs may be used. According to other embodiments, other colors of LEDs or any combination of LEDs may be used (for example, red, green, blue, infrared, ultraviolet).

In the depicted embodiment, field of view118of forwards looking camera116is illuminated by two LEDs240aand240blocated within the endoscope head230and protected by optical window242aand242brespectively.

Similarly, in the depicted embodiment, field of views of side looking camera220is illuminated by a single LED250located within the endoscope head230and protected by optical window252. It should be noted that number of LED light sources and their position in respect to the cameras may vary within the scope of the current invention. For example few LEDs may be positioned behind the same protective window, a camera and an LED or plurality of LED may be located behind the same protective window, etc.

Head230of endoscope200is located at the distal end of a flexible shaft260. Similarly to shafts of the art, shaft260comprises a working channel262for insertion of surgical tools. Additionally, shaft260may comprises channels for irrigation, insufflation, suction and supplying liquid for washing the colon wall.

FIG.2cschematically depicts a cross section cutout of an endoscope200showing some details of the head230according to an exemplary embodiment of the current invention. For simplicity, details of one of the two side looking cameras are marked in the figure.

According to the current invention, head230of endoscope200comprises at least one side looking camera220. Each of cameras220is provided with an optical imaging system such as lens assemblies232and solid state detector arrays234. Front camera element256of camera220may be a flat protective window or an optical element used as part of the imaging system232.

FIG.2dschematically depicts a cross section of an endoscope200having multiple fields of view showing some details of the head230according to an exemplary embodiment of the current invention.

According to some embodiments of the current invention, the interior of the head230comprises forward looking and side looking cameras116and220, respectively. Cameras116and/or220comprise lens assemblies132and232(not shown), respectively, having a plurality of lenses430to434and protective glass436(not shown) and a solid state detector arrays134and234(not shown) connected to a printed circuit board135and235(not shown) respectively. It is noted that cameras116and220or any element related to them (such as lens assemblies132and232, lenses430to434and protective glass436, solid state detector arrays134and234and/or printed circuit board135and235) may be the same or different. In other words the front looking camera and the side looking camera(s) may be the same or different in any one or any combinations of their components or other element related to them (such as optical elements).

FIG.3schematically depicts a cross section of cameras116or220, showing some details of lens assemblies132and232according to an exemplary embodiment of the current invention. It should be noted that according to some embodiments of the invention, cameras116and220may be similar or different. Optionally, the focusing distance of camera116is slightly different than that of camera220. Differences in focusing distances may be achieved, for example, by (slightly) changing the distance between the lenses that comprise the lens assemblies132and/or232, or between the lens assembly and the detector array.

Air gap “S” between lenses431and432acts as a stop. Air gap S may affect the focal range (the distance between the closest object and farther objects that can be imaged without excessive blurring caused by being out of optimal focusing of the lens system).

According to an exemplary embodiment of the current invention, cameras116and220comprise lens assemblies132and232respectively. The lens assemblies comprise a set of lenses430to434and protective glass436.

Lenses430to434are situated within a (optionally metallic) barrel410and connecter thereto (for example, glued in barrel410). Any one of lens assemblies132and/or232may also include an adapter411, optionally, as shown inFIG.3, positioned within barrel410. Adapter411is configured to adjust the location of one or more of the lenses and adjust the distance between lenses. Adapter411may also be configured to function as a stop (in this case, between lenses432and433. Protective glass436is situated in proximity to the solid state detector arrays134or234and is optionally attached thereto.

Focal distance (the distance to the object to be optimally focused by the lens system) may be changed by changing the distance between lenses434and protective glass436. As lens434is fixed to the barrel, and protective glass436is fixed to lens holder136(236), this distance may be varied by changing the relative positioning of lens holder136(236) with respect to barrel410. The space between the lenses434and protective glass436may be an empty space or may be filled with glass or other transparent material, or a tubular spacer may be inserted to guarantee the correct distance between these lenses. Optionally, optical filters may be placed within the space. Cameras116and220further comprise solid state detector arrays134and234respectively. Solid state detector arrays134and234may each be connected to printed circuit boards. An electrical cabling may connect the printed boards to a central control system unit of the endoscope.

Solid state detector arrays134and234are attached to lens holders136and236respectively. Lens holder136or236are attached to lens assemblies132or232respectively by attaching detector array cover to barrel410.

In some applications, protective glass436may be a flat-flat optical element, acting primarily as a protection of the detector array (such as detector arrays134and234), and may optionally be supplied with the array. However, optical properties of protective glass436need to be accounted for in the optical design.

In order to assemble lens assemblies132or232, lens430may first be inserted from left, then431, and432from right. Lenses433and434which may be glued together (or separated for example by air) are then inserted from right. The complete set is now assembled in a barrel. The assembled detector (such as detector arrays134and234), protective glass436and cover136(236) are then added.

FIGS.4a,4band4cillustrate three examples for the lens assemblies such as lens assemblies132and232according to the present invention, having objective lens systems510,520and530respectively. The sensor used in the lens assemblies132and232, according to this exemplary embodiment, may be a Charge Coupled Device sensor (CCD) having an array of micro-lenses but other sensors, such as CMOS, may also be used.

In an exemplary embodiment of the invention, a color CCD camera having resolution of approximately 800×600 pixels were used with total active area of approximately 3.3×2.95 mm. The optical resolution of the lens, according to exemplary embodiments of the current invention, was designed to match the resolution of the sensor. The objective lens system510(520/530) are preferably corrected for chromatic; spherical and astigmatism aberrations. In an exemplary embodiment of the invention, objective lens system510(520/530) is approximately 4.60 mm (4.62) total length, measured from front face of front lens to the front surface of the sensor. In an exemplary embodiment of the invention, objective lens systems510and520are wide angle objectives having approximately 170 degrees acceptance angle. In an exemplary embodiment of the invention, objective lens system510(520/530) has a short focal distance of measured from the front surface of the front lens to the imaged object. In an exemplary embodiment of the invention objective lens system510(520/530) has Depth of Focus (DOF) allowing to effectively image objects between 4-110 mm (or between, 3.5-50 mm). In an exemplary embodiment of the invention, objective lens system510,520and530has maximum diameter of about 2.5 mm, defined by the diameter of the front lens, and is housed in a barrel having maximum outer diameter of approximately 3.6 mm. It should be noted that other design parameters may be selected within the general scope of the current invention.

The objective lens system510(520/530) has an optical axis “O” depicted by the dashed line. The lens system comprises a front sub-system510a(520a/530a) and a rear sub-system510b(520b/530b).

Front sub-system510a(520a) (FIGS.4a(4b)) comprises a front lens430(430′) located closest to the object to be viewed, having a negative power and lens431(431′) having a positive power.

Front lens430(430′) is oriented with its concave surface facing toward the optical image formed and away from the object to be viewed and optionally having a diameter substantially greater than the largest dimension of the rear sub-system510bin the direction perpendicular to the optical axis. Lens431(431′) has a positive power.

Rear sub-system510b(520b) comprises lenses432,433;434; and protective glass436(lenses432′;433′;434′; and436′), wherein432(432′), has a positive power.433(433′) has a positive power,434(434′) has a negative power, and436(436′) has essentially no optic power. It is noted that protective glass436(436′) may be a part of the sensor or a part of the rear sub-system510b(520b). Lenses433and434(433′ and434′) of the rear sub-system510b(520b) compose an achromatic sub-assembly (a compound achromatic sub-assembly as seen inFIG.4a, where lenses433and434are cemented or non-compound achromatic sub-assembly as seen inFIG.4b, where lens433′ and lens434′ are separated). Lens433(433′) may be biconvex with radius of curvature of its front surface being smaller than radius of curvature of its rear surface, as indicated in Tables T1, T2below.

Lens432of the objective lens systems510may have a focal length f432satisfying the following condition: f432≤1.8f, where f is the composite focal length of the total system. Particularly, for the data indicated in Table T1f432=2.05 and f=1.234 mm, the condition: f432≤1.8f is satisfied.

Lens432′ of the objective lens systems520may have a focal length f432satisfying the following condition: f432≤1.8f.

Particularly, for the data indicated in Table T2f432=2.05 and f=1.15 mm, the condition: f432≤1.8f is satisfied.

The lenses may be coated with an anti-reflection coating (AR coating) for further improving the efficiency of the lens assemblies132(232).

An effective aperture stop S1(S2) is formed between lenses431and432(431′ and432′). Effective aperture stop S1(S2) may separate between front sub-system510a(520a) and rear sub-system510b(520b).

Front sub-system530a(FIG.4c) comprises a front lens430″ located closest to the object to be viewed, having a negative power and lens431″, having a positive power. Front sub-system530a(FIG.4c) further comprises an additional front positive lens (such as the meniscus lens429) disposed between the first front negative lens430″ and the second front positive lens431″. Front lens430″ is oriented with its concave surface facing toward the optical image formed and away from the object to be viewed and optionally having a diameter substantially greater than the largest dimension of the rear sub-system530bin the direction perpendicular to the optical axis.

Rear sub-system530bcomprises lenses432″,433″,434″; and protective glass436″, wherein432″, has a positive power,433″ has a positive power,434″ has a negative power, and436″ has essentially no optic power. It is noted that protective glass436″ may be a part of the sensor or a part of the rear sub-system530b. Lenses433″ and434″ compose an achromatic sub-assembly of the rear sub-system530band may or may not be cemented to each other. Lens433″ may be biconvex with radius of curvature of its front surface being smaller than radius of curvature of its rear surface, as indicated in Table T3below.

Lens432″ of the objective lens systems530may have a focal length f432satisfying the following condition: f432″≤1.8f, where f is the composite focal length of the total system. Particularly, for the data indicated in Table T3f432″=2.26 and f=1.06 mm, the condition: f432″≤1.8f is satisfied.

The lenses may be coated with an anti-reflection coating (AR coating) for further improving the efficiency of the lens assemblies132(232).

An effective aperture stop S3is formed between lenses431″ and432″. Effective aperture stop S3may separate between front sub-system530aand rear sub-system530b.

Tables T1T2and T3summarize the parameters of lenses in the objective lens systems510,520and530, respectively, according to some embodiments of the current invention:

TABLE T1(FOV = 164°, DOF = 3-110 mm. f = 1.234 mm, total optical track 4.09 mm)Semi-DiameterSemi-DiameterLensTypeR1R2ThDGlassd1/2d2/2fmm430Negative150.70.20.18N-LASF31.20.64−0.837431Plano-convex0.9Infinity0.560.27N-LASF30.80.81.02S1Stop0.050.104432Plano-convexInfinity−1.00.750.09FK50.80.82.05433Biconvex1.93−4.20.750.005N-LAK221.11.12.13434Biconcave−4.24.440.30.65N-SF661.11.2−2.3436Protection GlassInfinityInfinity0.30N-BK71.51.5Infinity

TABLE T2(FOV = 164°, DOF = 3-110 mm, f = 1.15 mm, total optical track 4.09 mm)Semi-DiameterSemi-DiameterLensTypeR1R2ThDGlassd1/2d2/2fmm430Negative60.70.20.3N-LASF31.20.66−0.91431Plano-convex1.26Infinity0.500.27N-LASF30.80.81.43S1Stop0.050.105432Plano-convexInfinity−1.00.600.15FK50.80.82.05433Biconvex1.67−1.650.700.30FK50.950.951.83434Meniscus−1.33−12.00.350.40N-SF661.01.2−1.65436Protection GlassInfinityInfinity0.30N-BK71.51.5Infiniy

Table 3, shows an example of a six-component system also comprising an additional positive lens429(for example, as indicated in Table 3, a meniscus lens).

TABLE T3(FOV = 164°, DOF = 3-110 mm, f = 1.06 mm, total optical track 4.69 mm)Semi-DiameterSemi-DiameterLensTypeR1R2ThDGlassd1/2d2/2fmm430″Negative4.30.750.20.22N-LASF31.30.72−1.06429Meniscus0.950.90.440.18N-SF660.80.655.75431″Plano-convex2.0Infinity0.750.02N-LASF30.80.82.26S3Stop0.020.116432″Plano-convexInfinity−1.00.780N-PSK570.80.81.69433″Biconvex2.52−2.00.500.154YGH520.80.81.49434″Biconcav−1.4411.00.250.91PBH560.80.9−1.50436″Protection GlassInfinityInfinity0.30N-BK71.51.5InfiniyR?- radius of curvature of the lens front surface (front surface is the surface facing the direction of the object);R2- radius of curvature of the lens rear surface (facing away from the object);Th - thickness of the lens - from center of front surface to center of rear surface;Glass - lens glass type;d1- radius of the front optical surface of the lens;d2- radius of the rear optical surface of the lens;D - distance between components such as lenses, measured front center of rear surface of the component, such as lens to the front surface of the next optical element (in the case of a stop, S, the distance is measured front center of rear surface of a component on the front side of the stop, to the front surface of the next component),As commonly used, radius of curvature equal to infinity is interpreted as planar. All lenses are optionally spherical.

FIGS.4a,4band4calso show the propagation of five incident rays of light R1to R6through the objective lens system510,520and530respectively, from the front lens430(FIG.4a),430′ (FIG.4b) or430″ (FIG.4c) till the creating of an image of the object at an image plane.

Rays R1to R6, enter the lens assembly at angles α1(alpha 1) to α6(alpha 6), respectively, for example, essentially equal to the following angles: α1=0°, α2=45°, α3=60°, α4=75° and α5=84°. The corresponding incident angles (the angles between the light rays which have passed the micro-lenses of the sensor and the optical axis of the system) are1(beta 1)-6(beta 6). According to some embodiments, the chief incident angle (for example the incident angles forming by rays R6inFIGS.4a-4c) is larger than 20°, larger than 25°, larger than 30° or between about 20-40°. The lens system, according to some embodiments of the invention provides minimal distortion (for example, less than 80%).

The optical system assembly132(232) may be assembled by a method comprising the step of:Optionally, cementing the rear doublet of lenses433-434(433′-434′);and:Assembling in the barrel the front lenses430(430′);Assembling lens431(431′) in the barrel;Assembling lens432(432′) in the barrel;Assembling in the barrel, the rear doublet433-434(433′-434′); andNote that front lens430(430′) may be assembled last.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.