Abstract:
An inter-lens baffles unit for an imaging system is provided. The inter-baffle lens unit comprises at least two lens elements; a plurality of baffles positioned between the two lens elements, wherein the baffles are contoured to fit between the two lenses and to fill a volume between the lenses such that the baffles are parallel to an optical path of an imaging system.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    This disclosure relates generally to imaging systems, and more particularly, to optical imaging systems using baffles. 
         [0003]    2. Related Art 
         [0004]    Optical instruments are typically used to generate images of objects and may include cameras or telescopes. Both cameras and telescopes may be used for general everyday use or may be used in space vehicles (for example, satellites, space shuttles, nano-satellites, international space station and others). 
         [0005]    Optical instruments typically use imaging systems (also referred to as optical systems) to generate images. However, sometimes these images may have flare. Flare is the collective name for colored spots, ghost images or veils that impair or distort an image. Flare is typically caused by stray light from a source of light (for example, the sun) impinging on a frontal lens of an imaging system. Typically, stray light is propagated between lens elements before finally reaching an imaging film or a digital sensor. 
         [0006]    Controlling flare is desirable especially in imaging systems for space vehicle optical instruments because space vehicle optical instruments are exposed to extreme and intense illumination due to the absence of atmosphere in space. To form a clear and sharp image, it is desirable to block stray light rays from reaching a lens (or glass elements) of the imaging systems. Typically, imaging systems use sunshields (shades or hoods) for shielding a lens from stray light. The sunshields protrude from the imaging system. In addition, imaging systems may use a plurality of baffles (or vanes, used interchangeably) outside the optical path. Typically, baffles are placed perpendicular to the optical path of an imaging system for blocking the propagation of stray light. 
         [0007]    However, in conventional systems, baffles placed perpendicular to the optical path, and sunshields fail to effectively block stray light because stray light may still propagate and clutter (or degrade) a final image. 
         [0008]    Therefore there is a need for an optical imaging system for use in optical instruments that reduces flare and produces sharp and clear images. 
       SUMMARY 
       [0009]    In one embodiment, an inter-baffle lens unit for an imaging system is provided. The inter-baffle lens unit comprises at least two lens elements; and a plurality of baffles positioned between the two lens elements, wherein the baffles are contoured to fit between the two lenses and to fill a volume between the lenses such that the baffles are parallel to an optical path of the imaging system. 
         [0010]    In another embodiment, an optical system is provided. The optical system comprises at least a first lens and a second lens; an array of baffles positioned between the first lens and the second lens, forming a baffled lens unit; wherein the array is contoured to fit between the first and the second lens. 
         [0011]    In yet another embodiment, an optical system is provided. The optical system comprises a plurality of lenses; and an array of baffles positioned between two lenses, forming a baffled lens unit; wherein the array is contoured to fit between the two lenses, and each baffle is substantially parallel to an optical path of the optical system. 
         [0012]    This brief summary has been provided so that the nature of the disclosure may be understood quickly. A more complete understanding of the disclosure may be obtained by reference to the following detailed description of the preferred embodiments thereof in connection with the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The foregoing features and other features of the present disclosure will now be described with reference to the drawings of a preferred embodiment. In the drawings, the same components have the same reference numerals. The illustrated embodiment is intended to illustrate, but not to limit the disclosure. The drawings include the following Figures: 
           [0014]      FIG. 1  shows an imaging system with a lens hood and baffles perpendicular to an optical path; 
           [0015]      FIGS. 2A and 2B  show effects of stray light on images formed by the imaging system of  FIG. 1 ; 
           [0016]      FIG. 3A  shows an imaging system, according to an embodiment; 
           [0017]      FIG. 3B-3D  shows a schematic of a baffle structure according to one embodiment; and 
           [0018]      FIGS. 4A-4B  and  5 A- 5 B show a comparison of an image formed by a conventional imaging system and the imaging systems of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    In one aspect of the present disclosure an imaging system with an inter lens baffle system is provided. According to one embodiment, the imaging system of the present disclosure effectively rejects stray light and forms sharp and clear images. 
         [0020]    To facilitate an understanding of an imaging system of the present disclosure, first an overview of a typical imaging system will be described. The specific structural components of the imaging system of the present disclosure will then be described with specific reference to general structure. 
         [0021]      FIG. 1  shows an example of a conventional imaging system  100  with a plurality of lenses (or lens elements)  102 ,  104  and  106 . The incident light includes a chief ray (R,  111 ) and some unwanted light rays R′ ( 112 ,  113 ) (also referred to as stray light or stray light rays) The incident light rays (R  111 , R′  112  and R′  113 ) enter the imaging system  100  from a range of predetermined directions generally parallel to the axis of the imaging system. 
         [0022]    The chief ray ( 111 ) is generally the ray that starts at the end of an object that is imaged (not shown) and passes through the center of an aperture to form an image at image plane  120 . Some unwanted rays (R′,  112 ,  113 ) may be blocked by sunshields  110  (hood) from propagating within imaging system  100 . 
         [0023]    However, sunshield  110  may not prevent all of unwanted rays ( 112 ,  113 ) from making contact with lens elements ( 102 ,  104 ,  106 ), especially if some of these rays enter at an exclusion angle for imaging system  100 . Exclusion angle is an angle that barely blocks a ray of light and some light rays still propagate within imaging system  100 . Exclusion angle is inversely proportional to the length of sunshields  110 , i.e., longer the sunshield, smaller the exclusion angle, and smaller the chance of stray light entering and propagating in imaging system  100 . Ray R′  113  is an example of stray light ray at the exclusion angle, where the lens is not protected by the sunshield  110 . Stray light ray  113  strikes the first lens element  102  of imaging system  100  and propagates within imaging system  100  to form undesired spots. Therefore, imaging system  100  with sunshield  110  is still prone to stray light propagation, which adversely affects the image quality. It is desirable to minimize propagation of stray light and allow passage of chief ray (R,  111 ) to form a clear, sharp, and well defined image. 
         [0024]    It is to be understood that a lens may be made of plurality of lens elements. For the purposes of this disclosure, the term “lens elements” and “lens(es)” is used interchangeably. 
         [0025]    Imaging system  100  may also use a plurality of baffles  108  which are placed outside and substantially perpendicular to the designed optical path ( 110 A,  110 B). Even after the combined use of baffles  108  and sunshield  110 , stray light ( 112  and  113 ) may still propagate and degrade the final image. Also, sunshield  110  is long, fragile and hence maybe inconvenient, especially on space vehicle imaging systems. Furthermore, it may not be possible to use sunshields on imaging systems for missiles and other applications. It is to be understood that the term baffle (or baffle-vanes) may refer to a single annular ring or a plurality of annular rings. The term baffles or baffle-vanes may be used interchangeably throughout the description. 
         [0026]      FIGS. 2A and 2B  show images  210  and  212  formed by the imaging system  100 . Spots  210 A and  212 A on images  210  and  220  respectively are formed as a result of stray light propagation within the imaging system  100 . Spots  210 A and  212 A are undesirable. 
         [0027]    The adaptive embodiments described below minimize the effect of stray light  112  and  113 . 
         [0028]    In one embodiment, an imaging system is provided that forms a clear and sharp image even when the system is exposed to extreme illumination by a source of light (for example, the sun). The imaging system of the present disclosure effectively reduces stray light propagation within an imaging system. 
         [0029]      FIG. 3A  shows an imaging system  300 , according to an embodiment of the disclosure. The imaging system  300  includes a plurality of lens elements ( 302 ,  304 , and  306 ) and a plurality of baffles  308  placed between the lens elements ( 302  and  304 ) substantially parallel to an optical path. Baffles  308  block passage and propagation of stray light ( 312  and  313 ) within the imaging system  300 . Baffles  308  may be placed in the space between lens elements  302  and  304 . Preferably, baffles  308  may be contoured to fit between the lens elements ( 302  and  304 ). 
         [0030]    In one embodiments, baffles  308  are optically absorbing members. Baffles  308  may be constructed from carbon composite, plastic, thin black metallic material and similar other material. These optically absorbing baffles prevent propagation of unwanted stray light rays within the imaging system. 
         [0031]    The number of baffles  308  used in an imaging system  300  depends on the nature and type of lens ( 302 ,  304 ,  306 ) used in imaging system  300 . 
         [0032]    Baffles  308  are substantially parallel to an optical path of the incident rays ( 311 ,  312 , and  313 ). The parallel placement of baffles ( 308 ) helps in controlling the amount of light rays that reaches the film  310 . If the baffles went across the optical path, light may be lost from the desired target. Therefore, parallel placement of baffles keeps the baffles from removing too much desired light from the target. The chief ray R ( 311 ) passes through the center of pupil aperture  304 A, while the rays ( 312  and  313 ) pass through the edges of the pupil aperture  304 A. 
         [0033]    Further, for a portion of a field of view (V′), rays  312  and  313  are parallel to the optical path ( 311 ) of the incident light. Thus over a portion of the field of view, lens elements ( 302 ,  304 ) act as telecentric lenses having constant viewing angle at any point across pupil aperture  304 A. This enables elimination of stray light and formation of sharp and accurate images. 
         [0034]    In another embodiment, an array ( 320 ) of baffles (also referred to as “baffle array”  320 ) is formed (as shown in  FIGS. 3B and 3D ). Baffle array  320  comprises a plurality of planar baffles  308  arranged in rows and columns ( FIG. 3D ). Each planar baffle  308  is roughly parallel to the optical path of imaging system  300  ( FIG. 3A ). The number of baffles  308  in a baffle array  320  may vary depending on the type of lens in an optical system. As an example,  FIG. 3D  shows ten baffles in the baffle array  320 . In one embodiment, the baffle array may be formed of baffles having co-axial conical sections (not shown). 
         [0035]    Array  320  is disposed (sandwiched) between lenses  302  and  304 , to form a baffled lens unit  340  ( FIG. 3C ). Array  320  may be contoured in a shape conforming to the structure of lens  302  and  304 . Baffles  308  in the array  320  are made from optically absorbing material in one embodiment. Baffles may also be coated with an optically absorbing material in another embodiment. The optically absorbing baffles prevent propagation of stray light within the imaging system  300 . 
         [0036]    Array  320  has planar baffles which when placed between the lens elements  302  and  304  of imaging system  300  are substantially parallel to the optical path. As explained with respect to  FIG. 3A , planar baffles  308  placed in the imaging system  300  have lens elements ( 302  and  304 ) acting as telecentric lenses thereby preventing propagation of stray light. Imaging system  300  having an array  320  of planar baffles  308  positioned between consecutive lenses is able to effectively provide sharp and accurate images. 
         [0037]      FIG. 4A  shows an image  410  formed by a conventional imaging system  100 . Image  410  is cluttered due to the stray light effect.  FIG. 4B  shows an image  420  formed by imaging system  300  of the present disclosure. Image  420  is sharper than image  410 . Imaging system  300  substantially reduces the effect of stray light on an image, according to one embodiment. 
         [0038]    In one embodiment, imaging system  300  forms a sharp image of targets that may be close to a source of light. As an example,  FIGS. 5A-5B  show images of a target which is proximal to the sun.  FIG. 5A  shows an image  510  formed by a conventional imaging system  100 . In image  510 , the target is not clearly visible because proximity to the sun causes flare in the image.  FIG. 5B  shows an image  520  formed by the imaging system  300  where the target is clearly seen. Imaging system  300  according to one embodiment provides sharp and clear images even when exposed to intense illumination by a source of light. 
         [0039]    The imaging system of the present disclosure is especially useful for use in missile and aircraft applications, where a sunshield or hood is undesirable or may not possible. Use of imaging systems with inter-lens baffle unit, significantly improves target visibility. The imaging system of the present disclosure may also be used in cameras where lens hoods are not preferred, for example single use disposable cameras. 
         [0040]    Although the present disclosure has been described with reference to specific embodiments, these embodiments are illustrative only and not limiting. Many other applications and embodiments of the present disclosure will be apparent in light of this disclosure and the following claims.