Abstract:
An optical macro adaptor assembly comprising two or more lens components arranged successively along the optical axis thereof, configured to be mounted in front of the objective lens of a telescope, and acting to reduce the minimum focus distance of the telescope to permit the telescope to be used in environments requiring a close focus. The optical macro assembly can be a Galilean-type optical system of approximately unit magnification with adjustable spacing between the lens elements to allow for focusing.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an optical macro accessory that reduces the minimum focus distance of a telescope system. 
       BACKGROUND 
       [0002]    Telescopic systems, such as spotting scopes and riflescopes, as well as astronomical and other telescope systems, typically do not have very close focus capability since this is not a requirement for the intended use of the device. For example, many astronomical telescopes cannot be focused on targets that are closer than several meters away. Likewise many spotting scopes used for various sport, hobby, and commercial applications lack close focus ability. Another telescope device is a riflescope. These are frequently designed to focus from infinity to about 50 meters and typically have only a very limited ability to adjust the focus. Even specialty rifle scopes which have adjustable objective lenses are not designed to focus on nearby targets only a few meters away. 
         [0003]    As a result, these telescopes cannot be used for applications in which a close focus capability is needed. Such close focus applications may include visual close-ups of nearby birds, insect studies in the field, and close inspection of equipment in nearby hazardous or inaccessible environments. In addition, the lack of a close focus capability makes testing or training uses of the telescope more cumbersome since a target placed nearby cannot be brought into focus. One example is telescopic photography system testing during which the optical system must be focused on a target. A different example is marksman “dry-fire” training during which various aspects of riflery can be practiced, such as trigger training during which a marksman observes the target through the scope while pulling the trigger to try and minimize the motion of the gun. The lack of a close-focus capability limits indoor applicant and training uses because many indoor facilities do not have very a long clear line of sight where the telescope and target can be set up. Similarly, the lack of a close-focus capability may prevent repurposing of existing telescope equipment for alternative applications requiring a close-focus. 
         [0004]    It is known to use a fixed single-element conversion lens attached to the front of a conventional camera lens to increase or decrease the lens&#39; focal length and allow for an increased zoom capability, such as a 2× tele-converter for converting a 3× zoom to a 6× zoom lens or a 0.5× wide angle converter providing a wide angle or even a “fisheye” field of view. However, it is not always desired to substantially alter the magnification or field of view of a lens system Accordingly, it would be beneficial to provide an optical macro adaptor which can be coupled to the objective end of a telescope and provide the telescope system with a closer than normal telescopic focus range while preserving the telescope&#39;s magnification and field of view. 
         [0005]    It is known to attach a single lens stopped down by about ⅔ of its diameter to the front of rifle scope to provide for a limited close-focus capability. The stopping is a conventional way to avoid introducing optical aberrations which would otherwise be caused by the portions of the lens far from its optical center. The extensive stopping provides a significant reduction in light gathering capability. As a result, this lens is suitable for use only in very bright conditions. 
         [0006]    It would be a further benefit to provide an adaptor that introduced minimal optical aberrations without requiring the lenses in the adaptors to be stopped down so that as much of the telescope&#39;s original aperture as possible can be utilized. 
         [0007]    It would be a further benefit if such an adaptor itself could be focused to provide additional flexibility of the telescope system in close-focus applications. 
       SUMMARY 
       [0008]    These and other issues are addressed by aspects of the present invention which provides an optical macro accessory that can be attached to the objective, end of a telescope to permit very close-focus. The macro adapter is comprised of a housing with two or ore lens modules arranged successively along the optical axis. The lens modules cooperate to form an optical assembly with approximately unit power and which operates to reduce the minimum focus distance of the telescope to which it is attached. In one embodiment, the optical modules of the adaptor are configured as a Galilean-type optical system in which the first lens module is a converging optical element and the second lens module is a diverging optical element. For example, the first lens module can be a single double convex lens and the second lens module can be a single double concave lens. 
         [0009]    The adaptor has a telescope mount that can connect the back of the adaptor to the objective side of the telescope. The mount can comprise threads on the adaptor which permit it to be screwed to the telescope directly or connected indirectly through the use of threaded rings of appropriate diameters. Alternatively, the telescope mount can include a metal, plastic, or rubber cylinder that slips over the end of the telescope tube. 
         [0010]    The simple function and compact design of the adaptor allows for convenient addition or removal from the telescope&#39;s front housing. The optical elements in the adaptor can be selected and arranged to provide the telescope with close focus capability without substantial alteration to the telescopic instrument&#39;s magnification, preserving the field of view of the instrument, and minimizing axial and lateral chromatic aberration and other optical aberrations over the focus range. Use of low cost, common glass types such as BAK4 and BK7, combined with anti-reflective coatings assure reasonable cost and retention of the telescopic instrument&#39;s inherent contrast. 
         [0011]    The adaptor can also he configured to allow for independent focusing as well by mounting the lens modules so as to allow their spacing to be varied axially between, for example about 4 mm to about 20 mm. When attached to the front of a telescopic system set to infinity focus, the adaptor can be used, for example, to bring objects from 50 meters to as close as 2 meters or less into focus. 
         [0012]    In one application, the adaptor can be attached to the end of an astronomical telescope lacking close focus capability so as to permit indoor testing of or practice in the use of the telescope for applications in which the operator must be able to bring an object into focus. In another application, the adaptor can be attached to the end of a riflescope to allow the scope to focus on a nearby target for trigger training and other applications. When used with a riflescope, the ability to focus the adaptor is particularly useful since rifle scopes often have limited or no applicable focusing ability. The adaptor&#39;s focus can thus be used to adjust the focus on the target instead of the operator having to change the distance between the entire rifle and the target to get a good focus. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0013]    These and other features and advantages of the invention, as well as structure and operation of various implementations of the invention, are disclosed in detail below with references to the accompanying drawings: 
           [0014]      FIG. 1  is a block diagram showing a cross section of a general embodiment of the adaptor according to aspects of the present invention and a telescope; and 
           [0015]      FIG. 2  is a schematic cross-sectional diagram of a particular embodiment of the adaptor according to aspects of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]    Turning to  FIG. 1 , there is shown a block diagram of a cross section of a general embodiment of the macro adaptor  10  according to the present invention. The adaptor  10  is shown adjacent a telescope  12  having an objective lens  14 , an eyepiece  16 , and an optical axis  18 . The telescope  12  has a typical focus distance from infinity to 50 meters. Telescope  12  can be any type of telescope such as a telescope for visual or photographic astronomy or observation, a rifle or other scope, or other type of instrument. The adaptor  10  and telescope  12  are conventionally cylindrical, with a circular cross-section, and this configuration is addressed herein. However, the invention is not so limited and the macro adaptor  10  can be used with telescopes of other configurations. 
         [0017]    The macro adaptor  10  has a housing  20  with first and second portions  22  and  24  and a central optical axis  26 . A first lens module  28  is mounted in the first portion of the housing  22  and second lens module  30  is mounted in the second portion of the housing  24 . Both lens modules  28 ,  30  are aligned with the optical axis  26 . The first and second tens modules cooperate to form an optical assembly with approximately unit power and which, when the second portion  30  of the adaptor  10  is mounted to the objective end of the telescope  12 , operate to reduce the minimum focus distance of the telescope. In a more specific embodiment, the first and second lens modules form a Galilean-type optical system in which the first lens module is a converging optical element and the second lens module is a diverging optical element. Even more specifically, the first lens module can be a single double convex lens and the second lens module can be a single double concave lens. One or more doublet or other compound lenses can be used instead and other alternative lens configurations are also possible. A Galilean optical assembly allows for a compact configuration that preserves image orientation and can be configured to maintain the telescope&#39;s field of view without requiring the lenses in the adaptor  10  to be stopped down to reduce optical aberrations. Non-Galilean optical configurations may also be used, although they may be less suitable for the applications discussed herein. One such alternative may include two widely spaced positive lenses with a focal point between them. 
         [0018]    The second portion  24  of the adaptor  10  has a mounting part which can be used to attach the adaptor  10  directly or indirectly to the objective end of the telescope  12  so that the optical axis  26  of the adaptor is aligned with the optical axis  18  of the telescope. Various configurations can be used for this purpose and mounting part will typically include a threaded portion on the second portion  24  adaptor  10 . In  FIG. 1 , a metal, plastic, or rubber cylinder  32  that is sized to slip snugly over the end of the telescope tube is removably attached to the end of the second portion  24  of adapter  10 , although it could be permanently mounted instead. Screws (not shown) can be provided to hold the cylinder  32  in place on the telescope. Alternatively, and as discussed further with respect to  FIG. 2 , the adaptor  10  can be attached to the telescope by a threaded assembly on second portion  24  that can be screwed into corresponding threads on the end of the telescope  12  directly or by means of one or more threaded rings. A wide variety of threaded mounting rings are commercially available permitting a single sized adaptor  10  to be easily coupled to a variety of differently sized telescopes. Other mounting configurations can also be used. 
         [0019]    The adaptor  10  can also be configured to allow for focusing by mounting the lens modules  28 ,  30  so that their axial spacing can easily be adjusted by a user. The range of adjustable spacing for focusing can be selected based on the specific optical parameters of the adaptor  10  and the type of device to which it may be intended to connect and whether that device has its own focusing ability which may be used when the adaptor  10  is mounted. A variety of focusing mechanisms known to those of skill in the art can be used, such as a rack and pinion, Crayford, or helical focuser designs. In particular embodiments, the focusing mechanism used can be similar to that in the TeleVue® Paracorr™ coma corrector with a slidable barrel and clamping screw or the TeleVue® DeLite™ eyepiece with a slidable barrel and locking ring. 
         [0020]      FIG. 2  shows one specific embodiment of the adaptor  10  configured as a Galilean-type optical system in which the first lens module is a converging optical element and the second lens module is a diverging optical element. In the illustrated embodiment of  FIG. 2 , the first lens module is a single double convex lens  48  with an outer radius R 1  and an inner radius R 2 . The second lens module is a single double concave lens  50  with an inner radius R 3  and an outer radius R 4 . 
         [0021]    In one configuration of the embodiment of  FIG. 2 , lens  48  has an axial thickness of about 4 mm, an outer Radius R 1  of about 150 mm and an inner Radius R 2  of about −290 mm. Lens  48  is formed of a material with a refractive index of about 1.5, such as 1.517, and an Abbe number of about 64, such as 64.2. A suitable material is BK7 glass. Lens  50  has an axial thickness of about 3 mm, an inner Radius R 3  of about −220 mm and an outer Radius R 4  of about 220 mm. Lens  50  is formed of a material with a refractive index of about 1.6, such as 1.569, and an Abbe number of about 56, such as 56.3. A suitable material is BAK4 glass. Anti-reflection coatings may also be applied to the lenses. 
         [0022]    The mounting part shown in  FIG. 2  is comprised of a threaded portion  60  along the outside of the end of the second portion  24  which permits the adaptor  10  to be connected directly or indirectly to the objective end of the telescope  12 .  FIG. 2  shows a mounting ring  62  screwed onto the threaded portion  60 . The mounting ring  62  has additional threads  64  which can be engaged to a corresponding threaded portion of the telescope or to other differently sized rings as needed to fit the adaptor to the objective end of the telescope  12 . In addition, as noted above, instead of rings, a suitably sized mounting cylinder that fits over the objective end of the telescope  12  can be provided. 
         [0023]    The spacing between lens  48  and  50  can be varied by moving the second portion  24  axially relative to the first portion  2  of the adaptor  10 . The second portion  24  is supported within the first portion  22  by a frictional bushing  70 . The focus can be locked by a locking ring  72  which can be turned to increase or decrease the pressure on the frictional bushing  70 . A felt ring  74  can be provided to help maintain axial alignment of the second portion  24  as it is moved in and out of the first portion  22 . In this most specific embodiment, the lens spacing can be varied across a range of from about 4 mm to about 20 mm. When attached to the front of a telescopic system set to infinity focus, the adaptor can be used, for example, to bring objects from 50 meters to as close as 2 meters distance into focus. This generally unit-power Galilean arrangement avoids introducing aberrations that might compromise instrument resolution, axial and lateral chromatic aberration or field of view of the instrument. Its simple function and compact design allows it to be conveniently added to or removed from telescope&#39;s front housing. Use of low cost, common glass types and multi-coatings assure reasonable cost and retention of the instrument&#39;s inherent contrast. 
         [0024]    Various aspects of the invention have been disclosed and described herein. However, various modifications, additions and alterations may be made by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.