Patent GB-905242-A (GB)
Title: Improvements in or relating to combination exposure meter and/or filter selector devices
IPC: G01J1/42
Filed: 1959-05-25
Abstract: 905,242. Exposure meters and filter selectors. INGBER, O. H. May 25, 1959 [May 27, 1958], No. 17688/59. Classes 97 (1) and 98 (1). An exposure meter and filter selector for determining the exposure setting and colour filter for a camera comprises an objective for forming an image of the object to be photographed, means for producing auxiliary luminous images which can be compared with the object image, and means for adjusting the relative photometric and colorimetric characteristics of the object image and the auxiliary images, whereby the different adjustments will provide readings for the camera exposure and filter settings, and means for rendering the characteristics of visual accommodation of the observer's eye fixed during viewing. In the embodiment shown in Figs. 1, 2 an image of an object is formed by objective 2 on a ground glass screen 6a and is viewed through an eyepiece 32. The objective is provided with a stop (not shown) and a detachable light-absorbing screen 3 for varying the intensity of the object image. The colour may be altered by one of a series of filters on a rotatable frustrum 4 (which could be a disc or cylinder). This adjustment enables the camera objective filter to be chosen. A grid 12 is provided adjacent screen 6a and is illuminated by lamps 10, 11 which are provided with adjustable filters 22a. By varying the relative lumination of the grid and the object image the intensity of the grid can be made to correspond to different parts of the object image and the range of allowable camera exposure times and diaphragm apertures can be determined. The grid could alternatively comprise reflecting strips, incandescent filaments or spots of phosphorescent paint, and could be illuminated with ultra-violet light. To allow three separate exposure determinations for three trichromatic components of the colour image to be made three adjustable monochromatic filters 33a are provided in front of the eyepiece. A bright frame comprising windows 13, 14 illuminated by lamps 10, 11 is produced adjacent screen 6a and by varying filters 22a the brightness of the frame is varied to take into account the film sensitivity since the accommodation of the eye is affected by this frame. A series of comparative images are formed on a film 26 and one of them which corresponds in subject to the object is projected by lamp 15 on to a screen 6b adjacent the object image. Lamp 15 may give intermittent illumination. By adjusting either the stop on objective 2 or a series of lightabsorbing filters 16 the relative intensities of the images on screen 6 can be varied to get a desired effect and the camera diaphragm aperture and exposure time determined from these adjustments. The comparative images could be mounted on cylinders, discs or frusti of cones. An absorbing wedge 34a is removably mounted in front of the eyepiece 32 so that in an alternative method the wedge can be moved in front of the eyepiece and by varying the stop on objectives 2 and determining when the darkest details on the object image are no longer distinguishable the correct exposure can be determined. The various adjusting means described above may be coupled to corresponding parts in the camera so that these parts are automatically set when the exposure meter is adjusted. In another embodiment, several comparative images of varying photometric and colorimetric characteristics may be viewed simultaneously. In a further embodiment the intensity of the lamps illuminating the grid 12 is varied by means of an adjustable resistance in their electrical circuit and converging lenses may be placed adjacent screen 6.