GB2516098A

GB2516098A - Viewfinders

Info

Publication number: GB2516098A
Application number: GB1312479.7A
Authority: GB
Inventors: Richard Simpson; Craig Whitehill
Original assignee: EYEFINDER Ltd
Current assignee: EYEFINDER Ltd
Priority date: 2013-07-12
Filing date: 2013-07-12
Publication date: 2015-01-14
Also published as: GB201312479D0

Abstract

A viewfinder arrangement 70 is configured to be removably attached to a camera. The viewfinder arrangement 70 comprises an optical arrangement in an afocal configuration. The optical arrangement comprises an objective lens arrangement 24 which is configured to provide a discontinuous change in a field of view seen through the viewfinder arrangement. The viewfinder may be attached to a hot shoe on a camera via an attachment plate 32.

Description

Title of Invention: Viewfinders

Field of the Invention

The present invention relates to a viewfinder arrangement and in particular but not exclusively to an optical viewfinder arrangement which is configured to be removably attached to a camera. The present invention also relates to a camera arrangement comprising a camera, such as a digital camera, and such a viewfinder arrangement.

Background Art

Viewfinders are used by photographers to compose pictures. An optical viewfinder (OVE) forms part of the long used twin-lens reflex (TLR) camera and the more recently introduced single-lens reflex (SLR) camera. TLR and SLR cameras comprise a mirror. The mirror is operative in the TLR camera such that a scene is viewed and a picture of the scene is taken by way of separate lenses whereas in the SLR camera the mirror is operative such that a scene is viewed and the picture is taken by way of the same lens. Development of electronic imaging technology led to the introduction of the digital camera and the electronic viewfinder (EVE). An EVE comprises a lens arrangement and an electronic display device such as a small LCD or OLED display which are operative to display the scene being viewed to the photographer and which is viewed when the camera is held close to the eye. An EVF is either integrated with or removably attached to the camera. Many photographers consider the OVF to be superior to the EVF on account of certain advantages including the OVF providing "full resolution" (i.e. the resolution of the photographer's eye).

The mirror-less interchangeable lens camera (MILC) or compact system camera (CSC) is an increasingly popular class of digital system camera. The CSC comprises an interchangeable lens mount and lacks a through-the-lens OVF. A picture is often composed in such a CSC by way of a large LCD display on the rear of the camera which can be viewed when the camera is held at arm's length. Some CSCs, however, comprise an integrated EVE whereby a picture can be composed without the inconvenience of viewing the LCD at arm's length. The interchangeable lens mount of the CSC provides for mounting of lenses of different focal lengths, i.e. fixed focal length (or prime) lenses and variable focal length (or zoom) lenses.

Although the lens selection for CSCs is limited at present compared with the digital SLR lens market, the increase in popularity of the CSC is accompanied by an increase in the selection of CSC lenses.

Mindful of the disadvantages of EVFs compared with OVFs, the present inventors have become appreciative of the change in the field of view required of a viewfinder when lenses of different focal lengths are mounted on a CSC. The present invention has been devised in the light of this appreciation. It is therefore an object for the present invention to provide a viewfinder arrangement which is configured to be removably attached to a camera, such as a compact system camera (CSC), and which is configured to accommodate a change in the focal length of a taking lens arrangement of the camera.

Statement of Invention

According to a first aspect of the present invention there is provided a viewfinder arrangement which is configured to be removably attached to a camera, the viewfinder arrangement comprising an optical arrangement in an afocal configuration, the optical arrangement comprising an objective lens arrangement which is configured to provide a discontinuous change in a field of view seen through the viewfinder arrangement.

The optical arrangement comprised in the viewfinder arrangement comprises an objective lens arrangement which is configured to provide a discontinuous change in a field of view seen through the viewfinder arrangement. A photographer may therefore change the field of view seen through the viewfinder arrangement when a taking lens having one focal length is changed for a taking lens having a second focal length. For example a lens having a focal length of 28mm may be changed for a lens having a focal length of 38mm. The present invention may therefore applied to advantageous effect where prime lenses are used or where zoom lenses which are set by the photographer to a specific focal length are used. The field of view of the camera to which the viewfinder arrangement is removably attached depends on the width of the camera's optical sensor as well as the focal length of the taking lens.

Changing the field of view seen through the viewfinder arrangement may therefore accommodate a change in optical sensor width, for example when the viewfinder arrangement is removably attached in turn to a first camera having a 35 mm wide optical sensor and to a second camera having a 23.5 mm wide optical sensor. The objective lens arrangement is configured to provide a discontinuous change in a field of view seen through the viewfinder arrangement. The objective lens arrangement may provide for a change between spaced apart field of view figures such as between a horizontal field of view of 500 and a horizontal field of view of 65°. The objective lens arrangement may therefore be configured such that there is no continuous change in the field of view seen through the viewfinder arrangement.

The viewfinder arrangement may be an optical viewfinder and thus may lack electro-optic components present in EVEs. A physical path of the optical arrangement may be substantially the same as a length of the optical path defined by the optical arrangement. An axis of the optical path defined by the optical arrangement may therefore be substantially straight. A viewfinder arrangement in which the physical path and the optical path are of substantially the same length may be more compact and less expensive than a viewfinder arrangement which employs folded optics. The configuration of a viewfinder arrangement in which the physical path and the optical path are of substantially the same length and which accommodates a relatively wide

field of view is described below.

The objective lens arrangement may comprise a plurality of objective lenses having different optical characteristics. Each of the plurality of objective lenses may be configured to removably attach to a main body of the viewfinder arrangement with one of the plurality of objective lenses being attached at any one time to the main body. In use, only one of the plurality of objective lenses may be attached at any one time to the main body. The different characteristics of the plurality of objective lenses may provide for different fields of view seen through the viewfinder arrangement. More specifically the plurality of objective lenses may consist of two objective lenses. Each of the objective lenses may be held in an objective lens holder. An objective lens may be removably attached to the main body by way of at least one pair of magnets, such as a pair of neodymium magnets. Each of the plurality of objective lenses may be a negative lens. Each of the plurality of objective lenses may be an aspheric lens. At least one of the plurality of objective lenses may be a negative meniscus lens. At least one of the plurality of objective lenses may be a piano-concave lens. Where the plurality of objective lenses consists of two objective lenses, a first objective lens may be a negative meniscus lens and a second objective lens may be a piano-concave lens. A negative meniscus lens may provide for a wider field of view than a piano-concave lens. Each of the plurality of objective lenses may be disposed such that its concave surface is directed away from the objective end of the viewfinder arrangement.

The viewfinder arrangement may comprise a field of view arrangement which is operative to provide for a discontinuous change in a field of view seen through the viewfinder arrangement. The field of view arrangement may provide for a change in the field of view in addition to the change provided by the objective lens arrangement. The field of view arrangement may be operative to provide for a smaller step change in field of view compared with the step change in field of view provided by the objective lens arrangement. The objective lens arrangement may therefore be operative to provide a crude change in the field of view and the field of view arrangement may be operative to provide a fine change in the field of view. For example the objective lens arrangement may provide for a change between a horizontal field of view of 50° and a horizontal field of view of 65° and the field of view arrangement may provide for three step reductions of about 4° from each of the 50° and 65° field of view figures. The field of view arrangement may be configured to define plural apertures of different dimensions and may be disposed in the optical path defined by the optical arrangement to thereby provide a restricted field of view.

The field of view arrangement may comprise plural field of view apparatus which define different respective apertures. Each of the plural field of view apparatus may be configured to removably attach to a main body of the viewfinder arrangement with one of the plurality of field of view apparatus being attached at any one time to the main body. The different apertures defined by the plural field of view apparatus may provide for different fields of view seen through the viewfinder arrangement. A field of view apparatus may be attached to the main body by being held between the main body and a holding arrangement. The field of view apparatus may be attached towards an ocular end of the main body. The holding arrangement may be a unitary member which defines an aperture. Where the optical arrangement comprises an ocular lens arrangement, as described below, the ocular lens arrangement may be comprised in the holding arrangement. The field of view apparatus may therefore be disposed in the optical path between the ocular lens arrangement and the objective lens arrangement. The holding arrangement may be removably attached to the main body by way of at least one pair of magnets, such as a pair of neodymium magnets.

The plurality of field of view apparatus may consist of four field of view apparatus.

A field of view apparatus may be unitary. A field of view apparatus may comprise a frame formed, for example, from injection moulded thermoplastic, which holds a transparent member formed, for example, from optical grade polycarbonate. The transparent member may be disposed in the optical path of the viewfinder arrangement. The transparent member may be configured to define a desired optical aperture, i.e. an aperture which allows the passage of light. Different transparent members may therefore define different desired apertures to thereby provide for a discontinuous change in the field of view seen through the viewfinder arrangement.

The viewfinder arrangement may be configured to make use of the Albada principle.

It is known to use the Albada principle to superimpose features, such as frame lines, on a scene viewed through optical apparatus while maintaining sharp focus of the superimposed features and the scene. In the present invention the Albada principle may be used to determine a field of view seen through the viewfinder arrangement.

More specifically the field of view apparatus may comprise a surface in the optical path of the viewfinder arrangement, the surface having a reflective periphery which surrounds a non-reflective part of the surface. The reflective periphery may be defined by a silvered coating. The surface having the reflective periphery may be directed away from the ocular end of the viewfinder arrangement. The surface having the reflective periphery may be disposed in the viewfinder arrangement towards the ocular end of the viewfinder arrangement. The reflective periphery may therefore be out of focus to a user who views a scene through the ocular end of the viewfinder arrangement. The non-reflective part may be operative to define the field of view of the viewfinder arrangement. The surface having a reflective periphery may be comprised in the field of view apparatus and more specifically may be a surface of a transparent member comprised in the field of view apparatus.

The viewfinder arrangement may further comprise a further surface in the optical path of the viewfinder arrangement, the further surface being operative to reflect a portion of light impinging on the further surface and to transmit a portion of light impinging on the further surface. The further surface may be configured, such as by way of a partially reflective coating, to transmit at least 50%, 60%, 70% or 80% of the impinging light. The further surface may be configured, such as by way of a partially reflective coating, to reflect no more than 50%, 40%, 70% or 20% of the impinging light. The further surface may be directed towards the ocular end of the viewfinder arrangement. The further surface may be disposed in the viewfinder arrangement towards the objective end of the viewfinder arrangement. The surface having the reflective periphery and the further surface may thus face each other. The further surface may be comprised in the intermediate lens arrangement, which is described below, and more specifically may be a surface of a second lens of the intermediate lens arrangement which of the lenses of the intermediate lens arrangement is closer to the ocular end of the viewfinder arrangement of the other lens or lenses of the intermediate lens arrangement. The surface having the reflective periphery and the further surface may be operative together to superimpose an image of the reflective periphery on the scene viewed by the user through the viewfinder arrangement.

Disposition of the further surface towards the objective end of the viewfinder arrangement may be such that the image of the reflective periphery is observed by the user to be in focus. More specifically an image of the reflective periphery may be reflected off the further surface towards the user's eye. A scene viewed through the viewfinder arrangement may therefore have an area around the periphery of the scene which is obscured yet discernible with the rest of the scene being at least less obscured if not substantially un-obscured. The field of view of the viewfinder arrangement may therefore be defined by the extent of the reflective periphery of the further surface. Where a field of view arrangement comprises plural field of view apparatus which define different respective apertures, the reflective peripheries on the plural field of view apparatus may be of different extents to thereby define the different respective apertures. In respect of each field of view apparatus, the part of the scene corresponding to the aperture defined by the field of view apparatus may be substantially un-obscured whereas the part of the scene corresponding to the part of the surface of the field of view apparatus having the reflective periphery may be obscured yet discernible.

The optical arrangement may comprise an ocular lens arrangement. The ocular lens arrangement may consist of an ocular lens. The ocular lens may be a positive lens.

Where the objective lens is a negative lens, the optical arrangement may therefore have a reverse Galilean configuration. The optical characteristics of the ocular lens arrangement may substantially match the other optical components in the optical path, such as the objective lens arrangement and the intermediate lens arrangement. The ocular lens may be an aspheric lens. The ocular lens may be a piano-convex lens. The ocular lens may be disposed such that its convex surface is directed towards the objective end of the viewfinder arrangement. The ocular lens arrangement may be comprised in the holding arrangement.

The optical arrangement may comprise an intermediate lens arrangement. The intermediate lens arrangement may be configured to determine the field of view seen through the viewfinder arrangement. Determination of the field of view may therefore depend on the optical characteristics of the objective lens arrangement and the intermediate lens arrangement. The viewfinder arrangement may however be configured to change the field of view in dependence on a change in the optical characteristics of the objective lens arrangement only of the objective lens arrangement and the intermediate lens arrangement. The optical characteristics of the objective lens arrangement and of the intermediate lens arrangement may be determined to minimise the contribution of the optical arrangement to aberrations.

Where the optical arrangement comprises an ocular lens arrangement, the intermediate lens arrangement may be disposed in the optical path between the ocular lens arrangement and the objective lens arrangement. Where the viewfinder arrangement comprises a field of view arrangement, the intermediate lens arrangement may be disposed in the optical path between the field of view arrangement and the objective lens arrangement. The intermediate lens arrangement may consist of first and second intermediate lenses. More specifically the first intermediate lens may be a negative meniscus lens. The second intermediate lens may be a bi-concave lens. The concave surfaces of the first and second negative meniscus lenses may face each other. An intermediate lens arrangement consisting of first and second lenses may be preferred to an intermediate lens arrangement consisting of a single lens because the former may provide a lower aberration contribution than the latter on account of the larger radius of curvature of the former.

The optical arrangement may comprise a subjective filter arrangement. The subjective filter arrangement may comprise a plurality of subjective filter apparatus.

Each of the plurality of subjective filter apparatus may be configured to provide a different effect, such as polarisation, colour or neutral density. Each of the plurality of subjective filter apparatus may be configured to removably attach to a main body of the viewfinder arrangement with one of the plurality of subjective filter apparatus being attached at any one time to the main body. A subjective filter apparatus may be attached to a main body of the viewfinder arrangement by being held between the main body and a filter holding arrangement. The subjective filter apparatus may be attached towards an objective end of the main body. The filter holding arrangement may be a unitary member which defines an optical aperture. The filter holding arrangement may be the objective lens arrangement described above.

Where the optical arrangement comprises an ocular lens arrangement, the subjective filter apparatus may be disposed in the optical path between the objective lens arrangement and the ocular lens arrangement. Where the viewfinder arrangement comprises an intermediate lens arrangement, the subjective filter apparatus may be disposed in the optical path between the objective lens arrangement and the intermediate lens arrangement. A subjective filter apparatus may be unitary. A subjective filter apparatus may comprise a frame formed, for example, from injection moulded thermoplastic, which holds a transparent member formed, for example, from optical grade polycarbonate. The transparent member may be disposed in the optical path of the viewfinder arrangement. The transparent member may comprise a coating which is operative to provide a required effect such as polarisation.

The optical arrangement may be configured to substantially maintain focus of scenes seen through the viewfinder arrangement greater than 5 metres, 2 metres, 1 metre or 0.5 metres from the objective end of the viewfinder arrangement. The eye relief of an optical arrangement is the greatest distance between the ocular end of the optical arrangement and the viewer's eye at which the full viewing angle of the optical arrangement can be used by the viewer. The present inventors were mindful that users of the viewfinder arrangement may wear spectacles and may therefore be unable to locate their eye close to the ocular end of the viewfinder arrangement. The optical arrangement may therefore be configured to provide for eye relief of up to 10 mm, 15 mm, 20 mm or 25 mm.

The viewfinder arrangement may comprise a main body. The main body may hold at least one of the ocular lens arrangement, the intermediate lens arrangement and the field of view arrangement. The main body may comprise a housing which is configured to support at least one component of the optical arrangement.

As mentioned above, the viewfinder arrangement is configured to be removably attached to a camera. The viewfinder arrangement may define a profile which is configured to engage with a corresponding profile on a camera. The profile defined by the viewfinder arrangement may be configured to engage with a profile often provided on different cameras. More specifically the profile defined by the viewfinder arrangement may be configured to engage with a mounting location such as a hot shoe on a camera.

The viewfinder arrangement may comprise an attachment arrangement which is configured for removable attachment to a camera, such as by way of a hot shoe connector. The attachment arrangement may be configured to allow for rotation of a main body of the viewfinder arrangement relative to the camera to which the viewfinder arrangement is attached. The attachment arrangement may comprise a rotation arresting arrangement which is operative to arrest rotation of the main body of the viewfinder arrangement relative to the camera. The rotation arresting arrangement may be configured to provide for free movement of the main body relative to the camera over plural spaced apart arcs and to provide for resistance to free movement between adjacent spaced apart arcs. More specifically relatively rotating first and second parts of the attachment arrangement may be configured to releasably interlock with each other between adjacent spaced apart arcs. One of the first and second parts of the attachment arrangement may comprise at least one recess and the other of the first and second parts may comprise at least one movable protrusion which is biased so as to be retractably received in a corresponding recess. Alternatively or in addition, the rotation arresting arrangement may comprise a rotatable ring which is rotatable between a first position which allows for free rotation and a second position in which rotation of the main body of the viewfinder arrangement relative to the camera is arrested. The attachment arrangement may comprise a spacer arrangement which is removable from the rest of the attachment arrangement and which when comprised in the attachment arrangement increases a separation between a main body of the viewfinder arrangement and a location at which the viewfinder arrangement removably attaches to a camera.

The viewfinder arrangement may be configured such that it defines a field of view having an aspect ratio of one of 16:9, 4:3 and 3:2. External dimensions of the viewfinder arrangement may correspond generally with the aspect ratio. A width of the viewfinder arrangement may thus be about 1.5 times a height of the viewfinder arrangement. A housing of the viewfinder arrangement may have an aspect ratio of 3:2. An aperture defined by the viewfinder arrangement may have an aspect ratio of 3:2. The housing of the viewfinder may be configured to define an aperture of aspect ratio of 3:2. For example the housing may extend from a periphery of lenses comprised in the optical arrangement in a direction perpendicular to an axis of the 0 optical path and towards the axis of the optical path to define the aperture. The viewfinder arrangement and more specifically a main body of the viewfinder arrangement may have a width between 20 mm and 60 mm, between 30 mm and 50 mm or between 35 mm and 45 mm. More specifically the viewfinder may have a width of about 42 mm. The viewfinder arrangement and more specifically a main body of the viewfinder arrangement may have a height between 10 mm and 50 mm, between 20 mm and 40 mm or between 25 mm and 35 mm. More specifically the viewfinder arrangement may have a height of about 29 mm. The viewfinder arrangement and more specifically a main body of the viewfinder arrangement may have a length (i.e. in a direction of the optical path) between 20 mm and 70 mm, between 30 mm and 60 mm or between 40 mm and 55 mm. More specifically the viewfinder arrangement may have a length of about 44 mm or 50 mm depending on the configuration of the objective lens arrangement in respect of a desired field of view. The length may be determined by the thickness of optical components comprised in the viewfinder arrangement and by the separation of the optical components from each other.

The viewfinder arrangement may be configured to provide a horizontal field of view of at least 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65° or 70°. The objective lens arrangement may be configured to provide for a step change in the horizontal field of view of at least 5°, 100 or 15°. The objective lens arrangement may be configured to provide for a step change in the horizontal field of view of no more than 20°, 15° or 10°. Where the viewfinder arrangement comprises a field of view arrangement, the field of view arrangement may be configured to provide for a step change in the horizontal field of view of at least 2°, 30, 4°, 5°, 6° or 7°. The field of view arrangement may be configured to provide for a step change in the horizontal field of view of no more than 8°, 7°, 6°, 5°, 4° or 3°.

At least one lens comprised in the viewfinder arrangement may be formed trom at least one of optical crown glass, high-index plastics material (thiourethanes) and optical plastics material, such as polycarbonate, PMMA or polystyrene. At least one face of at least one lens comprised in the viewfinder arrangement may have an anti-reflective coating such as a coating comprising magnesium fluoride.

The viewfinder arrangement may be configured to be attached to cameras of different classes. More specifically the viewfinder arrangement may be configured to be attached to different classes of digital cameras, such as compact system cameras (CSCs), or even different classes of non-digital cameras. According to a second aspect of the present invention there is therefore provided a camera arrangement comprising a camera, for example a digital system camera such as a compact system camera (CSC), and a viewfinder arrangement according to the first aspect of the present invention. Embodiments of the second aspect of the present invention may comprise one or more features of the first aspect of the present invention.

According to a further aspect of the present invention there is provided a viewfinder arrangement which is configured to be removably attached to a camera, the viewfinder arrangement comprising an optical arrangement, the viewfinder arrangement being configured to change a field of view seen through the viewfinder arrangement. Embodiments of the further aspect of the present invention may comprise one or more features of the first aspect of the present invention.

Brief Descrirtion of Drawings Further features and advantages of the present invention will become apparent from the following specific description, which is given by way of example only and with reference to the accompanying drawings, in which: Figure 1A is a perspective view from above, one side and the objective end of a first embodiment of the viewfinder arrangement of the present invention; Figure 1 B is a perspective view from below, one side and the ocular end of the first embodiment shown in Figure 1A; Figure 1 C is a perspective view from below, one side and the ocular end of a second embodiment of the viewfinder arrangement of the present invention; Figure 2 is an exploded perspective view from above, one side and the ocular end of the first embodiment shown in Figures 1 A and 1 B; Figure 3A is a representation of optical components comprised in a viewfinder arrangement according to the present invention configured to have a first field of view; Figure 3A is a representation of optical components comprised in a viewfinder arrangement according to the present invention configured to have a second field of view; Figure 4A is a view seen through the viewfinder arrangement when the viewfinder arrangement is configured to have a wide field of view; and Figure 4A is a view seen through the viewfinder arrangement when the viewfinder arrangement is configured to have a narrower field of view.

Description of Embodiments

A perspective view 10 from above, one side and the objective end of a first embodiment of the viewfinder arrangement is shown in Figure 1A. A perspective view 50 from below, one side and the ocular end of the first embodiment is shown in Figure 1 B. An exploded perspective view 70 from above, one side and the ocular end of the first embodiment is shown in Figure 2. The components of the first embodiment will now be described with reference to Figures 1A, 1 B and 2. The first embodiment of the viewfinder arrangement comprises a housing 12 of generally rectangular outline when viewed from each of the objective end and the ocular end of the viewfinder arrangement. The housing tapers between the objective end and the ocular end such the rectangle defined by the ocular end is smaller than the rectangle defined by the objective end. The housing is formed from an injection moulded thermoplastic material. The interior of the housing defines shaped profiles to accommodate and hold optical components of the viewfinder arrangement. The housing thus constitutes a main body of the viewfinder arrangement.

The first embodiment of the viewfinder arrangement also comprises a field of view apparatus 14 and an ocular lens arrangement 16. The ocular lens arrangement 16 is removably attached to the ocular end of the housing 12 by way of first and second pairs of neodymium magnets 18, 20. One of the first pair of magnets 18 is attached to one side of the ocular end of the housing 12 and the other of the first pair of magnets 18 is attached to one side of an end of the ocular lens arrangement 16.

One of the second pair of magnets 20 is attached to the other side of the ocular end of the housing 12 and the other of the second pair of magnets 20 is attached to the other side of the end of the ocular lens arrangement 16. The opposing ends of the housing 12 and the ocular lens arrangement 16 define recesses which are shaped to receive a protrusion 22 which extends from each of the top and the bottom of the field of view apparatus 14. The field of view apparatus 14 and the ocular lens arrangement 16 are attached to the housing 12 by positioning the field of view apparatus 14 between the ocular end of the housing 12 and the recessed and magnet bearing end of the ocular lens arrangement 16. Then the ocular lens arrangement 16 is attached to the housing by way of the magnets such that the field of view apparatus 14 is sandwiched between the ocular end of the housing 12 and the ocular lens arrangement 16 to thereby hold the field of view apparatus 14 in place.

The first embodiment of the viewfinder arrangement further comprises an objective lens arrangement 24 and a subjective filter arrangement 26. The objective lens arrangement 24 is removably attached to the objective end of the housing 12 by way of two pairs of neodymium magnets (not shown) which are disposed on opposite sides of the end of the objective lens arrangement 24 and the objective end of the housing 12 in the same fashion as described above with reference to the ocular lens arrangement 16. The objective end of the housing 12 and the magnet bearing end of the objective lens arrangement 24 define recesses which are shaped to receive a protrusion 28 which extends from each of the top and the bottom of the subjective filter arrangement 26. The objective lens arrangement 24 is attached to the housing 12 by way of the magnets such that the subjective filter arrangement 26 is sandwiched between the objective end of the housing 12 and the objective lens arrangement 24 to thereby hold the subjective filter arrangement 26 in place. The housing with the objective lens arrangement 24 in place is 41.2 mm wide and 28.9 mm high. When the objective lens arrangement 24 comprising the first objective lens 82, which is represented in Figure 3A, is attached to the housing the length of the viewfinder apparatus along the optical path is 50.4 mm. When the objective lens arrangement 24 comprising the second objective lens 102, which is represented in Figure 3B, is attached to the housing the length of the viewfinder apparatus along the optical path is 44.3 mm.

The first embodiment of the viewfinder arrangement yet further comprises an attachment arrangement 30 which is configured to provide for removable attachment of the viewfinder arrangement to a camera. Considering the attachment arrangement 30 further, the attachment arrangement 30 comprises a distal portion 32 which is shaped to mate with a hot shoe on a camera. The attachment arrangement 30 is formed at least in part from machined aluminium. The height of the viewfinder arrangement with the attachment arrangement 30 is 37.5 mm.

The ocular lens arrangement 16 comprises an ocular lens holder 34 formed from an injection moulded thermoplastic material which defines an aperture. The aperture is 19.8 mm wide and 12.87 mm high. The ocular lens holder 34 has an interior surface profile which holds an ocular lens. The ocular lens is described below with reference to Figures 3A and 3B. The field of view apparatus 14 comprises a frame 36 and a transparent member 38. The frame 36 is formed from an injection moulded thermoplastic material and defines an aperture. The transparent member 38 is formed from optical grade polycarbonate and is secured to the frame 36 such that it is disposed in the aperture defined by the frame 36. Field of view apparatus according to the invention consists of four different frames holding a respective transparent member with one of the frames being held in place on the housing 12 at any one time. The form of the different transparent members 38 is described further below with reference to Figures 3A and 3B.

The subjective filter arrangement 26 comprises a filter frame 40 and a filter member 42. The filter frame 40 is formed from an injection moulded thermoplastic material and defines an aperture. The filter member 42 is formed from optical grade polycarbonate and is secured to the filter frame 40 such that it is disposed in the aperture defined by the filter frame 40. The viewfinder arrangement comprises several different subjective filter arrangements. The filter member 42 of each subjective filter arrangement is configured to perform a different optical function. For example one filter member is configured to provide for polarisation, another is configured to filter one or more colours and yet another is configured to provide a neutral density effect. One of the several different subjective filter arrangements is held in place in the optical path of the viewfinder arrangement to match the optical effect of the viewfinder arrangement to the camera with which the viewfinder arrangement is being used, although no subjective filter arrangement is held in place if it is so desired. The objective lens arrangement 24 comprises an objective lens holder 44 which is formed from extruded aluminium and which defines an aperture.

The interior of the objective lens holder 44 is shaped to receive a frame member 46 which is formed from an injection moulded thermoplastic material. The frame member 46 defines an aperture which defines the greatest width and height of the optical path through the viewfinder arrangement. The objective lens arrangement 24 further comprises an objective lens. The viewfinder arrangement according to the present invention comprises two objective lens arrangements 24 having different optical characteristics which are determined by their respective objective lenses.

The optical characteristics of the two objective lens arrangements are described below with reference to Figures 3A and 3B.

A second embodiment of viewfinder arrangement 60 is shown in Figure 1 C. The second embodiment of the viewfinder arrangement 60 is the same in form and function as the first embodiment of viewfinder arrangement described with reference to Figures 1A, lB and 2 except as is described below. Features of the second embodiment in common with the first embodiment are indicated by like reference numerals. The reader's attention is therefore directed to the description provided above with reference to Figures 1A, lB and 2 for a description of such common features. Further to the first embodiment, the second embodiment 60 comprises a spacer arrangement 62 which is configured to releasably mate at a proximal end of the spacer arrangement with the distal portion 32 of the attachment arrangement 30.

The spacer arrangement 62 comprises a spacer distal portion 64 which is shaped to mate with a hot shoe on a camera. The spacer arrangement 62 is operative to increase the separation between the housing 12 of the viewfinder arrangement and the camera to provide for ease of use of the viewfinder arrangement or to provide for clearance between the housing 12 and components of a camera which might protrude from the camera in the vicinity of the hot shoe and otherwise impede proper use of the viewfinder arrangement. The spacer arrangement 62 is configured to provide for rotation of the housing 12 relative to the distal portion 62 by way of a rotation arrangement similar to a watch bezel rotation mechanism. More specifically the rotation arrangement comprises sprung ball bearings supported on a first part which are received in spaced apart recesses which define a circular path and are defined in a second part, the rotation arrangement being configured such that the first and second parts rotate relative to each other. The spacer arrangement 62 has a height of 18.5 mm, a width of 32 mm and a length of 32 mm.

The optical arrangement of the viewfinder apparatus will now be described with reference to Figures 3A and 3B. As stated above the viewfinder apparatus comprises two objective lens arrangements having different optical characteristics.

Figure 3A represents a first optical arrangement 80 comprising one of the objective lens arrangements and Figure 3B represents a second optical arrangement 100 comprising the other of the objective lens arrangements. The first and second optical arrangements 80, 100 are each configured to substantially maintain focus of views seen through the viewfinder arrangement greater than 0.5 metres from the objective end of the viewfinder arrangement. In addition the first and second optical arrangements 80, 100 are each configured to provide for eye relief of 25 mm from the ocular end of the viewfinder arrangement.

The first optical arrangement 80 comprises a first objective lens 82, a first intermediate lens 84, a second intermediate lens 86, a field of view arrangement 88 and an ocular lens 90. The first and second intermediate lenses 84, 86 together constitute an intermediate lens arrangement. The first objective lens 82 is an aspheric negative meniscus lens. The first intermediate lens 84 is a negative meniscus lens and the second intermediate lens 86 is a bi-concave lens which are disposed in relation to each other such that their concave surfaces are opposing.

The ocular lens 90 is an aspheric piano-convex lens with the convex surface directed towards the first objective lens 82. The first optical arrangement 80 is operative to provide a 65° horizontal field of view to a user viewing a scene through the viewfinder arrangement from the ocular end. The length of the first optical arrangement 80 is 48.4 mm from the objectively directed surface of the objective lens 82 to the surface of the ocular lens 90 closer to the eye when in use. The prescription for the first optical arrangement 80 is provided in Table 1 below. In column one of Table 1 the second surface refers to the objectively directed surface of the first objective lens 82.

Surf Radius (mm) Thickness (mm) Glass Diameter (mm) Conic 2 86 2 PMMA 44 0 3 25 10 36 -1.4 4 E 200 E 2 PMMA 32 E 0 22.8 8 28 0 6 -60 25 PMMA 27 7 7 150 19.9 30 0 8 Infinity 1 PMMA 21 0 9 Infinity 0 21 0 29 3 POLYCARBONATE 22 -0.2 11 Infinity 25 22 0

Table 1

The second optical arrangement 100 has the same form and function as the first optical arrangement 80 described above except as is described below. Features of the second optical arrangement 100 in common with the first optical arrangement 80 are indicated by like reference numerals. The reader's attention is therefore directed to the description above of the first optical arrangement 80 for a description of such common features. The second optical arrangement 100 comprises a second objective lens 102 instead of the first objective lens 82 of the first optical arrangement 80. The second objective lens 102 is an aspheric piano-concave lens with its concave surface directed towards the first intermediate lens 84. The second optical arrangement 100 is operative to provide a 5Q horizontal field of view to a user viewing a scene through the viewfinder arrangement from the ocular end. The length of the second optical arrangement 100 is 42.9mm from the objectively directed surface of the second objective lens 102 to the surface of the ocular lens 90 closer to the eye when in use. The prescription for the second optical arrangement is provided in Table 2 below. In column one of Table 2 the second surface refers to the objectively directed surface of the second objective lens 102.

Surf Radius (mm) Thickness (mm) Glass Diameter (mm) Conic 2 Infinity 2 PMMA 34 0 3 38 4 30 -8 4 200 2 PMMA 32 0 228 8 28 0 6 -60 25 PMMA 27 7 7 150 199 30 0 8 Infinity 1 PMMA 22 0 9 Infinity 0 22 0 29 3 POLYCARBONATE 22 -0 2 11 Infinity 25 22 0

Table 2

All the optical surfaces of the lenses of the first and second optical arrangements 80, 100 have an anti-reflection coating. The ocular end directed surface of the second intermediate lens 86 of each of the first and second optical arrangements 80, 100 has a partially reflective and partially transmissive coating. The coating is configured to transmit no less than 50% of the incident light. The transparent member of the field of view arrangement 88 of each of the first and second optical arrangements 80, 100 has a reflective coating on a part of the surface that is directed towards the objective end of the viewfinder arrangement. As described above the viewfinder arrangement comprises four different field of view arrangements with one of the four field of view arrangements being held in place on the housing 12 of the viewfinder arrangement at any one time. The reflective coating on each of the four field of view arrangements extends from an edge of the transparent member towards a centre of the transparent member with the reflective coating on different transparent members extending by a different amount. Each transparent member therefore comprises a peripheral area which reflects incident light and an area surrounded by the peripheral area which transmits light. The surrounded area is of different dimensions in the four different field of view arrangements. The reflective peripheral area and the partially reflective coating on the second intermediate lens 86 are operative together in accordance with the Albada principle to superimpose an image of the reflective peripheral area on the scene viewed by the user through the viewfinder arrangement. Each of the four field of view arrangements provides for a view which is obscured yet discernible where the image of the reflective peripheral area is superimposed, with the rest of the view being at least less obscured if not substantially un-obscured such that the rest of the view constitutes an effective field of view. The different sizes of the reflective peripheral areas of the four field of view arrangements provide for four different effective fields of view. The four field of view arrangements comprise further reflective portions in the central area that provides the effective field of view. Such further reflective portions define the like of cross-hairs.

Table 3 below specifies the Albada frame width (i.e. the width of the central non-reflective area) for eight different field of view arrangements. The first column in Table 3 specifies the focal length of the optical arrangement in mm, the second column specifies the full horizontal field of view in degrees, the third column specifies the horizontal field of view in mm at the surface of the ocular lens 90 closer to the user when the viewfinder arrangement is in use and the fourth column specifies the Albada frame width in mm. The first four rows in Table 3 relate to a first four different field of view arrangements when used with the first objective lens 82 and the fifth to eighth rows relate to a second tour different field of view arrangements when used with the second objective lens 102. The eight different field of view arrangements are therefore selectively used to provide for a fine step reduction in the effective field of view with the first and second lenses 82, 102 being selectively used to provide a

crude step change in the field of view.

Focal Length (mm) Full HF0V (deg) HF0V(mm at lens) Albada Frame Width (mm) 28 65.46 15.00 21.00 61.92 14.00 20.00 5443 1200 1660 38 5069 1105 1500 4845 1500 2100 43.60 13.33 18.60 39.59 12.00 14.60 33.40 10.00 12.60

Table 3

In the invention as described above, the same four different field of view arrangements are used with each of the first and second objective lenses 82, 102 and the sizes of the peripheral areas defined by the field of view arrangements are changed from the dimensions shown in Table 3 to provide for appropriate fine step

reductions in the effective field of view.

Figure 4A shows a scene seen through the viewfinder arrangement when using a field of view arrangement that provides for a small reduction in the effective field of view. Figure 4B shows the scene seen through the viewfinder arrangement when using a field of view arrangement that provides for a larger reduction in the effective field of view. As is evident from Figures 4A and 4B the part of the scene in the central, effective field of view is substantially un-obscured whereas the part of the scene in the peripheral area is obscured yet discernible.

Claims

Claims 1. A viewfinder arrangement which is configured to be removably attached to a camera, the viewfinder arrangement comprising an optical arrangement in an afocal configuration, the optical arrangement comprising an objective lens arrangement which is configured to provide a discontinuous change in a field of view seen through the viewfinder arrangement.
2. A viewfinder arrangement according to claim 1 in which the viewfinder arrangement is an optical viewfinder.
3. A viewfinder arrangement according to claim 1 or 2 in which a length of a linear physical path of the optical arrangement is substantially the same as a length of an optical path defined by the optical arrangement.
4. A viewfinder arrangement according to any one of the preceding claims in o which the objective lens arrangement comprises a plurality of objective lenses having different optical characteristics, each of the plurality of objective lenses being configured to removably attach to a main body of the viewfinder arrangement with one of the plurality of objective lenses being attached at any one time to the main body.
5. A viewfinder arrangement according to claim 4 in which the plurality of objective lenses consists of two objective lenses.
6. A viewfinder arrangement according to claim 4 or 5 in which each of the plurality of objective lenses is a negative lens.
7. A viewfinder arrangement according to any one of claims 4 to 6 in which each of the plurality of objective lenses is an aspheric lens.
8. A viewfinder arrangement according to any one of claims 4 to 7 in which a first objective lens is a negative meniscus lens and a second objective lens is a pIano-concave lens.
9. A viewfinder arrangement according to any one of the preceding claims comprising a field of view arrangement which is operative to provide for a discontinuous change in a field of view seen through the viewfinder arrangement.
10. A viewfinder arrangement according to claim 9 in which the field of view arrangement is operative to provide for a smaller step change in field of view compared with a step change in field of view provided by the objective lens arrangement.
11. A viewfinder arrangement according to claim 9 or 10 in which the field of view is arrangement is configured to define plural apertures of different dimensions and is disposed in an optical path defined by the optical arrangement to thereby provide arestricted field of view.

C.. . .
12. A viewfinder arrangement according to any one of claims 9 to 11 in which the field of view arrangement comprises plural field of view apparatus which define different respective apertures, each of the plural field of view apparatus being configured to removably attach to a main body of the viewfinder arrangement with one of the plurality of field of view apparatus being attached at any one time to the main body.
13. A viewfinder arrangement according to claim 12 in which the field of view apparatus is attached to the main body towards an ocular end of the main body.
14. A viewfinder arrangement according to claim 12 or 13 further comprising an ocular lens arrangement, the viewfinder arrangement being configured such that the field of view apparatus is disposed in an optical path of the viewfinder arrangement between the ocular lens arrangement and the objective lens arrangement.
15. A viewfinder arrangement according to any one of claims 12 to 14 in which a field of view apparatus comprises a frame holding a transparent member which is disposed in the optical path of the viewfinder arrangement, different transparent members of the plural field of view apparatus defining different apertures to thereby provide for a discontinuous change in the field of view seen through the viewfinder arrangement.
16. A viewfinder arrangement according to any one claims 12 to 15 in which the field of view apparatus comprises a surface in the optical path of the viewfinder arrangement, the surface having a reflective periphery which surrounds a non-reflective part of the surface, the surface having the reflective periphery being directed away from the ocular end of the viewfinder arrangement and the surface having the reflective periphery being disposed in the viewfinder arrangement towards the ocular end of the viewfinder arrangement.
17. A viewfinder arrangement according to claim 16 further comprising a further o surface in the optical path of the viewfinder arrangement, the further surface being operative to reflect a portion of light impinging on the further surface and to transmit a portion of light impinging on the further surface, the further surface being directed towards the ocular end of the viewfinder arrangement and the further surface being disposed in the viewfinder arrangement towards the objective end of the viewfinder arrangement.
18. A viewfinder arrangement according to any one of the preceding claims in which the optical arrangement comprises an ocular lens arrangement.
19. A viewfinder arrangement according to claim 18 in which the ocular lens arrangement consists of an ocular lens.
20. A viewfinder arrangement according to claim 19 in which the objective lens arrangement comprises an objective lens, the ocular lens being a positive lens and the objective lens being a negative lens whereby the optical arrangement has a reverse Galilean configuration.
21. A viewfinder arrangement according to claim 20 in which the ocular lens is a piano-convex lens, the ocular lens being disposed such that its convex surface is directed towards the objective end of the viewfinder arrangement.
22. A viewfinder arrangement according to any one of the preceding claims in which the optical arrangement comprises an intermediate lens arrangement which is configured to determine the field of view seen through the viewfinder arrangement, the viewfinder arrangement being configured to change the field of view in dependence on a change in the optical characteristics of the objective lens arrangement only of the objective lens arrangement and the intermediate lens arrangement.
23. A viewfinder arrangement according to claim 22 in which the intermediate lens is arrangement consists of first and second intermediate lenses, the first intermediate lens being a negative meniscus lens and the second intermediate lens being a bi-concave ens. C.. .
24. A viewfinder arrangement according to any one of the preceding claims configured to substantially maintain focus of scenes seen through the viewfinder arrangement greater than one of 5 metres, 2 metres, 1 metre and 0.5 metres from an objective end of the viewfinder arrangement.
25. A viewfinder arrangement according to any one of the preceding claims configured to define a field of view having an aspect ratio of one of 16:9, 4:3 and 3:2.
26. A camera arrangement comprising a camera and a viewfinder arrangement according to any one of the preceding claims.