GB2078935A - Colour-separating optical system with positioned photodetector - Google Patents

Abstract

An optical system 210 comprising an optical member 240, 250, 260 having an axis, a detector 225 disposed adjacent to said optical member along said axis and having an image area thereon for receiving light rays emitted from said optical member, and positioning means 270A, 270B and 270C including a rigid body disposed between said optical member and said detector and secured to each fixedly to hold said detector in a predetermined position with respect to said optical member and said axis, said rigid body having an opening 272 therethrough to accommodate uninterrupted passage of light rays from said optical member to said image area of said detector. <IMAGE>

Description

SPECIFICATION Colour-separating optical system The present invention relates to optical systems such as video color cameras in which it is imperative that individual detectors be very accurately positioned with respect to associated optical members.

More particularly, each detector must be carefully positioned without tilt with respect to a certain optical axis of the optical system, must be carefully positioned in directions parallel to and perpendicular to that axis, and the three detectors must be positioned without rotation relative to each other.

This positioning is particularly critical and delicate in connection with very small solid-state detectors such as charge-injection devices. In conventional video cameras expensive and complicated detector mountings have been necessary to insure maintenance of each detector in its predetermined position.

According to the invention there is provided an optical system comprising an optical member having an axis, a detector disposed adjacent to said optical member along said axis and having an image area thereon for receiving light rays emitted from said optical member, characterized by positioning means including a rigid body disposed between said optical member and said detector and secured to each fixedly to hold said detector in a predetermined position with respect to said optical member and said axis, said rigid body having an opening therethrough to accommodate uninterrupted passage of light rays from said optical member to said image area of said detector.

Figure 1 is a schematic side elevational view of the prism system of the present invention, illustrating the relationship of the prism system with the associated solid-state detectors of a video camera; Figure 2 is a graph of the color transmission characterisics of the prism system of Figure 1; Figure 3 is a view similar to Figure 1 of a prism system using dichroic plates cemented to the prisms to form the dichroic layers; Figure 4 is a view similar to Figure 1, and illustrating means for mounting the detectors with respect to the prism system; and Figure 5 is a view in vertical section taken along the line 5-5 in Figure 4.

Referring to Figure 1 of the drawings, there is illustrated an optical system, generally designated by the numeral 10, constructed in accordance with and embodying the features of the present invention for separating color components of incident light and directing those color components respectively to three solid-state detector units 20A, 20B and 20C of a small portable color video camera. The detector 20A-C are substantially identical in construction, each being in the form of a charge injection device comprising a detector element 25 embedded in a ceramic substrate 26, the obverse face of which is covered with a glass plate 27. The dimensions of the detector element 25 are such as to afford a sensitive image area having a height of .343 inch (8.7 mm) and a width of .457 inch (11.6 mm).The video camera also preferably includes a zoom objective lens (not shown) disposed to the left of the optical system 10, as viewed in Figure 1, which directs light rays to the optical system 10, the objective lens system preferably being Fix .4, substantially telecentric and vignetting-free for the image height.

The optical system 10 has a non-reflecting optical axis 30, and includes three prisms, respectively designated by the numerals 40, 50 and 60, each of which prisms is preferably formed of SF4 glass having an index of refraction of 1.755 and a dispersive constant of 27.6. The prism 40 has a flat entrance face 41 disposed substantially normal to the non-reflecting optical axis 30, an exit face 42 inclined with respect to the entrance face 41 at an angle of 23 30', and an exit face 43 inclined with respect to the entrance face 41 at an angle of substantially 47". The exit face 43 is preferably fitted with a blue absorption filter 44. Coating the exit surface 42 is a dichroic layer 45, the characteristic of which is such that it reflects the blue component of incident light and passes the remaining component of the light.The orientation of the exit face 42 is such that it reflects the blue component of the light back toward the entrance face 41 which, in turn, totally internally reflects the blue light toward the exit face 43, so that the blue light is emitted from the exit face 43 and through an absorption filter 44 generally along an exit path, the axis of which has been designated by the numeral 47.

The prism 50 has a flat entrance face 51 which is disposed parallel to the exit face 42 of the prism 40 and is spaced therefrom by an air gap, generally designated by the numeral 56. The prism 50 has an exit face 52 which is inclined at an angle of 36 to the entrance face 51 and an exit face 53 which is inclined with respect to the entrance face 41 of the prism 40 substantially at an angle of 72". Disposed on the exit face 52 of the prism 50 is a dichroic layer 55, the characteristic of which is such that it reflects the red component of incident light and passes the remaining component.

From the foregoing it is apparent that the dichroic layer 45 is disposed at an angle of 23.5 with respect to a plane perpendicular to the non-reflecting optical axis 30, while the dichroic layer 55 is inclined at an angle of 12.5 with respect to a plane perpendicular to the non-reflecting optical axis 30. The orientation of the dichroic layer 55 is such that the incident red light component is reflected toward the entrance face 51 which, because it forms a boundary with the air gap 56, totally internally reflects the red light component toward the exit face 53 for emission therefrom generally along an exit path, the axis of which has been designated by the numeral 57.

The prism 60 has an entrance face 61 which is cemented to the exit face 52 of the prism 50, with the dichroic layer 55 being disposed therebetween. The prism 60 also has a flat exit face 63 which is disposed perpendicular to the non reflecting optical axis 30.

Provided along the peripheral edges of the prism 60 is a plurality of baffle notches 64 of varying depths.

In Figure 1 there are depicted a plurality of oblique incident light rays, including the rays aO, bo, c0, do, eO, and fO. The rays aO and do are in the cone of rays which form a point at the upper edge of the object image, the rays bo and eO are in the cone of rays which form the point at the center or axis of the object image, and the rays c0 and f0 are in the cone of rays forming a point at the lower edge of the object image. The rays aO and f0 are limiting oblique rays, while the rays bo and eO are in the axial bundle of rays. Axial and oblique bundles are substantially equal.

By way of example, the path of the ray bo will be traced through the optical system 10. It will be understood that the other rays undergo similar reflections, although only a few of the rays have been traced to the exit faces of the system in the interest of simplicity of the drawing. The ray bo is incident on the entrance face 41 of the prism 40 and is refracted, the refracted ray being incident on the first dichroic layer 45, with the blue component bb being reflected back toward the entrance face 41, while the remaining component b1 of the ray passes through the dichroic layer 45 and the air gap 56 and is incident on the prism 50 at the entrance face 51 thereof.The blue component bb of the ray is totally internally reflected at the entrance face 41 of the prism 40 and exits through the exit face 43 and the blue absorption filter 44 thereof for transmission to the detector unit 20A at the center thereof.

The remaining component b1 of the ray is incident on the second dichroic layer 55, the red component brthereof being reflected back toward the entrance face 51, while the remaining green component: bg thereof passes through the dichroic layer 55 and enters the prism 60 at the entrance face 61 thereof.

The red component br of the ray is totally internally reflected at the entrance face 51 and exits through the exit face 53 for transmission to the detector unit 208 at the center thereof. The remaining green component bg of the ray exits the prism 60 at the exit face 63 thereof for transmission to the detector unit 20C at the center thereof.

Thus, it can be seen that at the first dichroic layer 45 the blue component of the incident light is separated and is reflected for emission from the optical system 10 at the exit face 43 to form the image on the blue light detector unit 20A, while the red component of the incident light is reflected at the second dichroic layer 55 for forming the image on the red light detector unit 208, and the green light component is transmitted directly and unreflected through the optical system 10 for emission therefrom at the exit face 63 to form an image on the green light detector unit 20C.

In a constructional model ofthe optical system 10, the overall length D between the entrance face 41 of the prism 40 and the exit face 63 of the prism 60 is 1.1 (27.94 mm) inches. The effective height H of the entrance face 41 of the prism 40, i.e., the vertical distance between the point at which the uppermost limiting oblique ray aO is incident on the front thereof and the point at which the blue component fb of the lowermost limiting oblique ray is internally reflected at the rear thereof is substantially .99 inch (25.15 mm). It will be appreciated that each of the overall length D and the effective height H is approximately three times the detector height (.343 inch) (8.71 mm).

Each of the exit faces 43,53 and 63 has an effective height, i.e., the distance between the exit points thereon of the uppermost and lowermost limiting oblique image-forming rays, which effective height is substantially .4 inch (10.16 mm). Thus, it can be appreciated that the effective heights of the exit faces 43, 53 and 63 are, respectively, slightly larger than but comparable to the corresponding heights (.343 inch (8.71 mm) of the associated detectors 25.

The equivalent air track of the optical system 10 is .626 inch (15.9 mm).

Figure 2 illustrates the color transmission characteristics of the optical system 10. This graph is a plot ofthewave-length of the light in nanometers, along the horizontal axis; against the percentage of incident light emitted from the system along the vertical axis. The lines 70 and 71 indicate the blue light emitted from the exit face 43, the lines 72 and 73 indicate the red light emitted from the exit face 53, and the lines 74 and 75 indicate the green light which is emitted from the exit face 63.

The graph of Figure 2 illustrates that the halfpower points are at 40% amplitude and, therefore, at 90% ofthefull-power peaks at least 72% of the blue component of the incident light in the wavelengths between about 395 nanometers and 480 nanometers is emitted from the optical system 10 at the exit face 43, at least 72% of the green component of the incident light in the wavelengths between about 500 nanometers and 570 nanometers is emitted from the exit face 63, and at least 72% of the red component of the incident light in the wavelengths between 590 nanometers and 645 nanometers is emitted from the system 10 at the exit face 53. It will also be noted that the system has fairly sharp cutoff between the color components, with the transmittance curve for each component rising from 90% of peak transmittance over a spectral range of only about 20 nanometers.

While the dichroic layers 45 and 55 have been disclosed above as coatings directly on the associated exit faces of the prisms 40 and 50, it will be understood that these dichroic layers could also be in the form of dichroic plates cemented to the associated prism faces. Referring to Figure 3 of the drawings, there is illustrated an optical system 110 which is substantially similar to the optical system 10, and includes three prisms, respectively generally designated by the numerals 140,150 and 160, and respectively substantially identical to the prisms 40, 50 and 60 described above. The prism 140 has an exit face 142 to which is attached a first glass dichroic plate 145, the dichroic plate 145 having an entrance face 144 which is cemented to the exit face 142 of the prism 140, and an exit face 146 on which is coated a dichroic coating or layer 147. The exit face 146 of the dichroic plate 145 is spaced by an air gap 148 from the entrance face 151 of the prism 150.

A dichroic plate 155 is secured to the exit face 152 of the prism 150, the dichroic plate 155 having an entrance face 154 on which is coated a dichroic coating or layer 157, and which is cemented to the exit face 152 of the prism 150. The dichroic plate 155 also has an exit face 156 which is cemented to the entrance face 161 of the prism 160.

It will be appreciated that the dichroic plates 145 and 155 could be made in any shapes, and it can be seen that the dichroic layer may be applied to either the entrance face or the exit face of the plate, depending upon the requirements of the particular system. However, the path length must remain equal for all three colors.

The use of such dichroic plates affords important manufacturing advantages. When dichroic coatings are applied directly to the faces of prisms, careful handling of the optical components is required during the coating process to prevent damage from chipping, and custom-made expensive tooling is necessary. Also, since the surfaces to be coated must be laid into holders, some margins of the surfaces will not receive coating. If the coatings turn out to be unacceptable, prisms must be stripped and recoated, a procedure which is very expensive and which subjects the prisms to the risk of additional damage.

The dichroic plate substrates, on the other hand, are preferably of commercially available thin sheet glass, and can be coated in large sizes and be cut to size afterwards. Thus, fewer workpieces are handled and spectophotometric testing is greatly simplified.

Should a coating be unacceptable, the substrate may simply be discarded since it is relatively inexpensive.

Coated plates are cut to exact size and cemented directly to the appropriate prism faces. Thus, coating extends over the entire face area with no voids.

Accordingly, the advantages of lower manufacturing cost and improved quality control are realized.

Referring now to Figures 4 and 5 of the drawings, there is illustrated an optical system 210 which is substantially identical to the optical system 10, and includes three prisms, respectively generally designated by the numerals 240,250 and 260 which are respectively provided with exit faces 243, 253 and 263. Respectively emitted from the exit faces 243, 253 and 263 along exit paths having axes 247, 257 and 267, are the blue, red and green color components which are separated at dichroic layers 245 and 255, the exit face 243 being provided with an absorption filter 244. Respectively disposed adjacent to the exit faces 243, 253 and 263 are three solidstate color detector units 220A, 2208 and 220C, each having a solid-state detector 225 and being respectively identical in construction to the detectors 20A-20C illustrated in Figure 1.The detector units 220A-220C are respectively fixedly held in position with respect to the associated prism exit faces (or associated absorption filter) by mounting and positioning bodies 270A, 270B and 270C, which are preferably of identical construction, whereby only one will be described in detail.

Referring in particulartothe mounting and positioning body 270C, it is in the form of a rectangular gasket 271 which has a rectangular opening 272 therethrough. Preferably, the gasket 271 is formed of a flexible, resilient, foamed body of material such as foamed rubber or the like dimensioned to be disposed between the detector unit 220C and the associated prism exit face 263 in contact with each and in surrounding relationship with the detector 225, the dimensions of the opening 272 being such as to permit uninterrupted transmission of imageforming light rays from the exit face 263 to the detector 225.

In assembling the detector 220C in the optical system 10, the porous, resilient gasket 271 is first inserted between the detector unit 220C and the associated prism exit face 263, in contact with each, and in surrounding relationship with the detector 225, which is the sensitive image area of the detector unit 220C. The detector unit 220C is then accurately positioned with respect to the exit face 263 and with respect to the exit path axis 267 thereof by the use of suitable micropositioners or the like. More particularly, the detector unit 220C is positioned so that the detector 225 is precisely located in the associated one of the three conjugate lens focal planes in order to process the sharpest possible image.It is, therefore, necessary to position the detector unit 220C without tilt, i.e., so that the optical axis 267 is perpendicular to the detector surface, in proper X-Y-Z location, i.e., at the proper distance from the exit face 263 and in the proper position in the focal plane, and without rotation relative to the other detector units 220A and 220B, i.e., with all rows and columns of the charge-injection devices mutually parallel.

When the detector unit 220C has been accurately positioned in the predetermined proper position with respect to the exit face 263 and the axis 267, an adhesive and hardening cement, such as epoxy or the like, is applied around the gasket 271 or injected thereinto so as to impregnate the porous gasket, while the detector unit 220C is held in its proper position. Thus, after the epoxy hardens it forms a rigid body which provides a secure, rigid bond between the detector unit 220C and the prism 260 for maintaining the predetermined proper positions thereof with respect to each other.

It will be understood that the detector units 220A and 220B are positioned and mounted in the same manner. Because of the different sizes of the exit faces 243, 253 and 263, the mounting and positioning bodies 270A-270C may be of slightly different sizes, as long as the opening 272 is sufficiently large to permit uninterrupted passage of light rays to the detectors 225. In a constructional model of the optical system 220, the detector units 220A-220C are respectively spaced from the associated prism exit faces (or associated absorption filter) by a distance of approximately 1 millimeter. Thus, the foamed gaskets 271 will initially have a thickness slightly greater than 1 millimeter to accommodate movement of the associated detector unit 220 during the positioning operation.

Thus, it can be seen that there has been provided a unique color-separating prism system of extremely small dimensions which is uniquely suitable for use with the minute injection device color detectors in small, hand-held video color cameras.

While there have been described what are at present considered to be the preferred embodiments of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

Claims (9)

1. An optical system comprising an optical member having an axis, a detector disposed adjacent to said optical member along said axis and having an image area thereon for receiving light rays emitted from said optical member, characterized by positioning means including a rigid body disposed between said optical member and said detector and secured to each fixedly to hold said detector in a predetermined position with respect to said optical member and said axis, said rigid body having an opening therethrough to accommodate uninterrupted passage of light rays from said optical memberto said image area of said detector.

2. The optical system of claim 1, characterized in that said rigid body effectively closes the area between said optical member and said detector in surrounding relationship with said image area of said detector.

3. The optical system of Claim 1 or Claim 2, characterized in that said rigid body comprises a porous body impregnated with a hardening and adhesive agent.

4. The optical system of claim 3, characterized in that said porous body is formed of foamed rubber and said hardening and adhesive agent is epoxy.

5. The optical system of Claims 1,2,3 or 4 adapted for use in a small portable video color camera further characterized by means for separating color components of light directed along a non-reflecting optical axis, said system comprising a prism assembly including first and second and third prisms and having a light entrance face on said first prism, a first dichroic plate fixedly secured to said first prism and spaced from said second prism by an air gap for receiving light entering said first prism through said input face and selectively reflecting a first color component while transmitting remaining light components to said second prism, a second dichroic plate disposed between said second and third prisms and fixedly secured to each for selectively reflecting a second color component while transmitting the remaining light component to said third prism, three exit faces respectively disposed on said three prisms for respectively emitting light components therefrom along three exit paths each having an axis, three detectors respectively disposed adjacent to said three exit faces and each having an image area thereon for receiving light rays emitted from the associated exit face, and three of said positioning means each including a rigid body disposed between the associated detector and the corresponding exit face and secured to each fixedly to hold the associated detector in a predetermined position with respect to the associated exit face and its axis, each said rigid body having an opening therethrough to accommodate uninterrupted passage of light rays from the corresponding exit face to said image area of said associated detector.

6. A method for making the optical system of any of Claims 1 through 5, characterized by the steps of placing between and in contact with the optical member and the detector a flexible body having an opening therethrough sufficient to permit uninterrupted passage of light rays from the optical mem berto the image area of the detector, adjusting the detector to a predetermined position with respect to the optical member and the axis thereof while maintaining the body in contact with the optical member and the detector, fixedly securing the body to the optical member and to the detector, and rigidifying the flexible body while holding the detector in said predetermined position thereby to form an assembly rigidly holding the detector in said predetermined position.

7. The method of Claim 6, characterized in that.

said flexible body comprises a porous resilient body and said rigidifying step comprises impregnating the porous body with a hardening and adhesive agent while holding the detector in said predetermined position, and allowing the agent to harden while holding the detector in the predetermined position.

8. The method of Claim 7, wherein said porous body is formed of foamed rubber and said hardening and adhesive agent is epoxy.

9. The features as herein disclosed, or their equivalents, in any novel selection.

9. An optical system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. The features as herein disclosed, or their equivalents, in any novel selection.

New claims or amendments to claims filed on 20 August1981.

Superseded Claims 1-10.

New or amended claims: CLAIMS

1. A method for making an optical system, characterized by the steps of placing between and in contact with an optical member and an optical detector a flexible body having an opening therethrough sufficient to permit uninterrupted passage of light rays from the optical member to the image area of the detector, adjusting the detector to a predetermined position with respect to the optical member and the axis thereof while maintaining the body in contact with the optical member and the detector, fixedly securing the body to the optical member and to the detector, and rigidifying the flexible body while holding the detector in said predetermined position thereby to form an assembly rigidly holding the detector in said predetermined position.

2. The method of Claim 1, characterized in that said flexible body comprises a porous resilient body and said rigidifying step comprises impregnating the porous body with a hardening and adhesive agent while holding the detector in said predetermined position, and allowing the agent to harden while holding the detector in the predetermined position.

3. The method of Claim 2, wherein said porous body is formed of foamed rubber and said hardening and adhesive agent is epoxy.

4. The method of any one of Claims 1,2 or 3 wherein the rigidification of the flexible body is permanent and irreversible.

5. An optical system comprising an optical member having an axis, a detector disposed adjacent to said optical member along said axis and having an image area thereon for receiving light rays emitted from said optical member, positioning means including a rigid body disposed between said optical member and said detector and secured to each fixedly to hold said detector in a predetermined position with respect to said optical member and said axis, said rigid body having an opening therethrough to accommodate uninterrupted passage of light rays from said optical member to said image area of said detector, and effectively enclosing the area between said optical member and said detector in surrounding relationship with said image area of said detector, characterized in that said rigid body comprises a porous body impregnated with a hardening and adhesive agent.

6. The optical system of Claim 5, characterized in that said porous body is formed of foamed rubber and said hardening and adhesive agent is epoxy.

7. The optical system of Claims 5 or 6 adapted for use in a small protable video color camera further characterized by means for separating color components of light directed along a non-reflecting optical axis, said system comprising a prism assembly including first and second and third prisms and having a light entrance face on said first prism, a first dichroic plate fixedly secured to said first prism and spaced from said second prism by an air gap for receiving light entering said first prism through said input face and selectively reflecting a first color component while transmitting remaining light components to said second prism, a second dichroic plate disposed between said second and third prisms and fixedly secured to each for selectively reflecting a second color component while transmitting the remaining light component to said third prism, three exit faces respectively disposed on said three prisms for respectively emitting light components therefrom along three exit paths each having an axis, three detectors respectively disposed adjacent to said three exit faces and each having an image area thereon for receiving light rays emitted from the associated exit face, and three of said positioning means each including a rigid body disposed between the associated detector and the corresponding exit face and secured to each fixedly to hold the associated detector in a predetermined position with respect to the associated exit face and its axis, each said rigid body having an opening therethrough to accommodate uninterrupted passage of light rays from the corresponding exit face to said image area of said associated detector.

8. An optical system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.