# US 5,708,860 A · Distance measurement apparatus and optical system using the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,708,860 A - Document ID: US5708860A - Status: Granted - Kind: A - Application number: 08/521,032 - Filed: 1995-08-29 - Granted: 1998-01-13 - Earliest claimed: 1994-08-31 - Assignees: Olympus Optical Co., Ltd. - Inventors: Osamu Nonaka; Kazunori Mizokami - Web page: https://patentgrep.com/patent/US5708860A ## CPC - G03B 17/08: Waterproof bodies or housings - G02B 7/32: using active means, e.g. light emitter {(including both an active and a passive focus detecting device G02B7/285; using ultrasound G02B7/40)} - G03B 7/16: in accordance with both the intensity of the flash source and the distance of the flash source from the object, e.g. in accordance with the "guide number" of the flash bulb and the focusing of the camera - G03B: APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D) - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract A CPU causes a Xe tube to emit light by charging a charging capacitor through an emission control circuit. Flash light from the Xe tube is projected toward an object to be measured through a mask, a visible light cutting filter, and a projection lens. Light reflected by the object is incident on a light-receiving element through a light-receiving lens and the visible light cutting filter. An output from the light-receiving element is input to a light position detection circuit. The CPU then calculates the distance to the object in accordance with an output from the light position detection circuit. A camera which can be used in water includes an electronic flash section capable of controlling its light amount. An underwater detection section detects whether the camera is used in water, and sends the detection result to a CPU. A distance measurement section projects a distance measurement light beam onto an object to be photographed, and measures the amount of light reflected by the object. The CPU estimates a light attenuation ratio in the environment where the camera is used on the basis of the detection result and the reflected light amount measurement result, and sets the amount of light to be emitted from the electronic flash section. With this operation, the electronic flash section is caused to emit light, and exposure in the camera is controlled by an exposure control section. ## Claims ### Claim 1 A camera comprising: underwater discrimination means for discriminating whether said camera is used in water; an electronic flash device for projecting auxiliary illumination light toward an object to be photographed in a photographing operation; and exposure control means for changing control of an exposure amount of flash light from said electronic flash device with respect to a film surface in accordance with a discrimination result obtained by said underwater discrimination means; and wherein said exposure control means controls an amount of light to be emitted from said electronic flash device in consideration of a light absorption coefficient .alpha. in water when said underwater discrimination means discriminates that said camera is in water, and wherein the light absorption coefficient .alpha. is predetermined in accordance with the light absorption characteristics of the water and is preset in the camera. ### Claim 2 A camera comprising: underwater discrimination means for discriminating whether said camera is used in water; an electronic flash device for projecting auxiliary illumination light toward an object to be photographed in a photographing operation; and exposure control means for changing control of an exposure amount of flash light from said electronic flash device with respect to a film surface in accordance with a discrimination result obtained by said underwater discrimination means; and wherein said exposure control means decides an f-number of a photographing lens in a light-emitting operation in consideration of a light absorption coefficient e in water when said underwater discrimination means discriminates that said camera is in water, and wherein the light absorption coefficient .alpha. is predetermined in accordance with the light absorption characteristics of the water and is preset in the camera. ### Claim 3 (depends on 1) A camera according to claim 1, further comprising photometric means for measuring a luminance of ambient light; and wherein said exposure control means compares a photometric value obtained by said photometric means with a determination level, and inhibits emission of light from said electronic flash device when the photometric value is higher than the determination level, and changes the determination level in accordance with a discrimination result obtained by said underwater discrimination means. ### Claim 4 (depends on 1) A camera according to claim 1, further comprising a magnetic recording apparatus which, and magnetically records a discrimination result obtained by said underwater discrimination means. ### Claim 5 (depends on 1) A camera according to claim 1, wherein said electronic flash device emits light containing a large amount of red-light components. ### Claim 6 (depends on 2) A camera according to claim 2, further comprising photometric means for measuring a luminance of ambient light; and wherein said exposure control means compares a photometric value obtained by said photometric means with a determination level, and inhibits emission of light from said electronic flash device when the photometric value is higher than the determination level, and changes the determination level in accordance with a discrimination result obtained by said underwater discrimination means. ### Claim 7 (depends on 2) A camera according to claim 2, further comprising a magnetic recording apparatus which magnetically records a discrimination result obtained by said underwater discrimination means. ### Claim 8 (depends on 2) A camera according to claim 2, wherein said electronic flash device emits light containing a large amount of red-light components.