Autofocus system

Abstract: An autofocus system employing a slave lens (33) which is so shaped or configured as to produce a strip of radiation (48) on a pair of detectors (45, 46) used in the autofocus system thus enabling an attractive and useful arrangement for photographic or video camera apparatus (Fig. 1).

Description: The present invention relates to an autofocus system according to the preamble of claim 1. In US-A-4 481 413 an improvement for autofocus devices used in, for example, video cameras is shown and described, wherein a totally reflecting strip mirror, rather than a larger partially reflecting mirror used in the prior art is provided, to divert a portion of the radiation from the camera taking lens to the autofocus circuitry for use in determining the correct position of the taking lens. The strip mirror produces a band of radiation which falls across a portion of the radiation detectors that are used in the autofocus system. In US-A-4 309 603 a system is shown wherein an auxiliary lens is mechanically connected to the camera taking lens and means are provided to move both the taking lens and the auxiliary lens simultaneously. The auxiliary lens is used to provide a path for radiation to the autofocus detectors rather than using any mirror to redirect a portion of the radiation from the taking lens thereto. The use of an auxiliary lens for autofocus has the advantage that all of the light going through the taking lens reaches the video electronics or film rather than diverting part of it to the autofocus circuitry. The use of the strip mirror also has certain advantages since 1) the detectors no longer have to be shaped in any particular configuration and are thus more easily manufactured 2) the percentage of the surface of the detectors covered by radiation is greater and there is less wasted light and 3) the adjustment of the optics so as to cause the radiation to fall on the detectors is more easily accomplished. One disadvantage of the slave lens system is that the additional lens configuration on the face of the camera is often unsightly. A disadvantage of the strip mirror is that some light is lost on reflection and the mirror physically takes up space in the camera which is often quite limited by the optical and elelctronic packages. An automatic focusing device for cameras which combines the advantages of the strip mirror system with those of the auxiliary lens system can be taken from US-A-3 682 071. There, a taking lens and an auxiliary lens both are displaceable by drive means. The image produced by the auxiliary lens is split-up by two wedges into two images which are received by two detectors via cylindrical lenses and field of view defining masks. Departing from this prior art device it is the object of the present invention to devise an autofocus camera where the front face of said camera is involved in the forming of the auxiliary image and the number of the used components is reduced. This object is achieved by the characterizing features of the independent claim. The present invention overcomes the problems in the prior art by providing, instead of a strip mirror, a regular lens having a mask thereover to form a slit aperture for the lens is provided. Thus a band of radiation for the detectors is provided without using a strip mirror and the slit mask can be placed on the exterior surface of the camera face in a variety of attractive arrangements not possible with a circular lens. A more complete understanding of the present invention will result from an examination of the following specification taken in connection with the attached drawings, where: Figure 1 is a perspective and diagramatic view of an arrangement not embodying the invention; Figure 2 is a perspective and diagramatic view of an embodiment of the present invention; Figure 3 is an enlarged view of a pair of detectors showing the band of radiation falling thereon; Figure 4 is a front view of a camera face utilizing the present invention; and Figure 5 is an enlarged view of a pair of detectors useful in connection with Figure 4. In Figures 1 and 2, the diagrams show a slave lens system similar to that described and claimed in the above-referred to patent 4,309,603. In Figure 1, the taking lens 10 of a photographic or video camera is shown which receives light from a remote object (not shown) to form an image thereof on a CCD detector array 12 of a video camera. It should be understood that in lieu of a CCD detector array as used in a video camera, the film of a photographic camera may be placed in the same position in which event a shutter which is shown in phantom by dash line 14 in Figure 1 would be employed so that after the taking lens 10 was moved to the proper focus position, the shutter would be opened or moved out of the way to thus expose the film. The CCD detector array 12 produces an output shown by arrow 18 to the video electronics 20 which processes the signals to produce an output shown by arrow 22 for storage on a magnetic tape or for use by the CRT of a video monitor. The taking lens 10 is shown in Figure 1 coupled by a mechanical connection shown as dash line 25 to a drive 28 by means of a second mechanical connection shown as dash line 30. Drive 28 will, as explained hereinafter, operate to position lens 10 at the proper focus position so that the image received by the CCD array 12 (or the film of a camera) will be in proper focus. An auxiliary or slave lens 33 is shown in Figure 1 connected to the drive 28 by the mechanical connection 30 and a third mechanical connection shown as dash line 35. Slave lens 33 is shown to be an elongated strip which may be cut from a normally circular lens shown in phantom by dash line 37. The purpose of the elongated configuration of lens 33 is to produce an elongated exit pupil which will then produce a band of radiation for use by the autofocus detectors as will be better explained hereinafter. Light from the remote object passes through the slave lens 33 to form an image on a lenslet array 40 having a plurality of tiny lenslets such as 42 formed therein. While only seven lenslets 42 have been shown in Figure 1, a much larger number (approximately 48) are normally employed. Mounted behind each of the lenslets 42 is a pair of detectors such as shown by lines 45 and 46. As will be more clearly understood by reference to 4,185,191, the individual detectors such as 45 and 46 each "see" an image of the exit pupil of the lens through which radiation from the object passes, in this case, lens 33. Since lens 33 is in an elongated strip shape, the image thereof will appear as an elongated strip image or band of radiation similar to that produced by the strip mirror of the above-mentioned patent 4,481,413. This image will be better described in connection with Figure 3 and is shown in Figure 1 by vertical line 48 lying across each of the detector pairs such as detectors 45 and 46. The outputs of the detector pairs such as 45 and 46 are presented by a connection shown as arrow 50 to the autofocus circuitry 52 which may be like that shown in the above-referred to patent 4,185,191. The output of the autofocus circuitry 52 is shown by an arrow 55 connected to the drive 28 which then operates through the mechanical connections 30, 25 and 35 to position lenses 10 and 33 at the proper focus position for the remote object. Figure 2 is substantially the same as Figure 1, except that instead of a strip shaped lens 33 as was shown in Figure 1, a regular lens 33′ is shown with a mask 60 located in front thereof. Mask 60 has a slit aperture 62 therethrough so that light from the remove object passes through the slot 62 to the lens 33′ and then onto the lenslet array 40. The slot 62 operates to produce an apparent exit pupil of lens 33 to be an elongated strip so that the detectors such as 45 and 46 will, again, "see" a strip of radiation such as shown by line 48. The remainder of Figure 2 is the same as Figure 1 and will not be further described here. Figure 3 shows one pair of detectors identified by reference numerals 70 and 72 spaced a short distance apart and being substantially square although their shape is a matter of design choice. Being of simple shape makes these detectors relatively easy to manufacture and to match. The elongated slit of radiation identified by reference numeral 75 is shown vertically lying across both of the detectors 70 and 72 at approximately the middle thereof. It is, however, not necessary that this be exactly In the middle so long as the band of radiation covers substantially the same area on both of the detectors. This also makes adjustment of the optics much easier as is more completely described in the above-mentioned patent 4,481,413. In Figure 4, the front of a video camera is shown having a normal circular taking lens 80 in the upper left-hand portion thereof. The slave lens is shown in Figure 4 as a diagonal slit 82 in the lower right-hand portion thereof which, is made to attractively cooperate with the letters "AF" that may be inscribed thereon for identifying the camera as an autofocus camera. Lens 82 can, of course, be either a lens formed into the desired elongated shape or may be circular with a slit in the front face of the camera as described in Figures 1 and 2 above. It will be understood that the slit or strip lens 82 can have all manner of different configurations in order to attractively fit within the necessary area of the camera face. Figure 5 shows the slit of radiation 87 which might be produced by the exit pupil shape of lens 82 of Figure 4 falling across a pair of detectors 89 and 90 which in Figure 5 are at an angle to one another so that the slit of radiation 87 falls across equal areas of both. It should be clear that the slit of radiation need not even be straight lines and that other shapes, for example the figure "S" could be used if desired, so long as the same amount of radiation from different portions of the "S" shape falls across both detectors.

Claims: An autofocus camera comprising: a taking lens (10,80); drive means (28,30,25) for driving the taking lens to a position where the image of a remote object is in proper focus; at least a pair of radiation detectors (45,46); an auxiliary lens (33) connected to the drive means to be movable with the taking lens; lenslet means (40,42) positioned between the detectors and the auxiliary lens means to form an image (48) of the exit pupil or the auxiliary lens on each of the at least one pair of detectors; and means (33',60) to configure the image of the exit pupil of the auxiliary lens into an elongated band (48,75,87), characterized in that said configuration means comprises a mask (60,82) adjacent the auxiliary lens, said mask being formed as a slit (82) in a front face of said camera.

Inventors: WILWERDING DENNIS J, WILWERDING, DENNIS J.
Applicants: HONEYWELL INC, HONEYWELL INC.
Application year: 1988
Main classification: G03B3
IPC codes: G02B7, G03B13