Since there seems to be a lot of interest in OM/Minolta OTF and
Flash patents here are a few references I dug up a while back when looking
into this for my own purposes. I have more references but don't have space
here. You can follow up more for yourself on the IBM or US patent office web
sites. Minolta has a number of fundamental patents but Olympus/Maitani/Cannon
etc have various enhancements and Olympus is still actively patenting a
variety of flash related ideas (including underwater photography recently).
Some of the more recent patents are for IS series cameras with dual tubes to
act as zoom etc. I have annoted the patents a bit (see sections in
parenthesis) here and included the first line of the claims but I may have
missed some so there may be other fundamental patents. Some of the Olympus
flash patents are interesting in that they give substantial circuit detail
and description in the patents specification section, and you realise FP
flash is not so easy to do.
Patents :
US3730063: DUAL LIGHT-RESPONSIVE AUTOMATIC EXPOSURE CONTROL APPARATUS
May. 1, 1973 / May. 11, 1971 (Minolta )
We claim :
1. In a photographic camera having light-responsive means for measuring scene
light through an objective lens, a capacitor connected to said light
responsive means to form an integrating circuit, a switching circuit
responsive to said integrating circuit, and means driven by said switching
circuit to initiate shutter closing after a delay period determined by said
integrating circuit, the improvement wherein said light-responsive means
comprises: a first photoconductive element mounted outside of the direct
light path from said objective lens to the light sensitive film surface and
responsive to light reflected from at least said light sensitive surface, and
a second photoconductive element mounted for receiving light transmitted
through said film.
US3687026: A LIGHT REFLECTIVE SHUTTER CONTROL APPARATUS
(OTF Minolta)
Aug. 29, 1972 / Nov. 13, 1970
A light scattering surface is mounted facing the objective lens to direct
light to a photoelectric detector during movement of a shutter curtain so
that shutter control is provided during the exposure. An integrating circuit
formed by a condenser and the photoelectric detector actuate a switching
circuit to control movement of a second shutter curtain to terminate the
exposure.
US3726197: APPARATUS FOR AUTOMATIC ELECTRONIC FLASH PHOTOGRAPHY
April 10, 1973 / March 26, 1970 (Cannon)
In the apparatus disclosed a photocell is mounted inside the camera and
directed toward the film of the camera. After the shutter of the camera is
snapped a flash is set off. A control system responds to the output of the
photocell to control the amount of light produced by the flash.
US3864699: AUTOMATIC EXPOSURE CONTROL SYSTEM FOR TTL METERING TYPE
SINGLE-LENS REFLEX CAMERA
( Cannon)
Feb. 4, 1975 / Sept. 6, 1973
In the TTL metering type single-lens reflex camera, a photoelectric converter
element disposed for receiving light from a viewfinder's optical system and a
photoelectric converter element disposed outwardly of such optical system for
receiving light reflected from a shutter curtain or a film surface after
flip-up of the viewing mirror are parallel-connected and have characteristics
selected to be substantially equal so that the rising and falling electrical
properties of these elements are utilized to accomplish a smooth transition
of exposure control.
US3842424: EXPOSURE CONTROL DEVICE IN SINGLE-LENS REFLEX CAMERA
Oct. 15, 1974 / April 11, 1973 (Cannon )
This invention relates to an exposure control device for automatically
controlling the shutter speed in a camera, especially a single-lens reflex
camera. It utilizes the reset time characteristic of a light receiving
element such as photoconductive cell or the like having a slow response
characteristic to control the camera shutter to a high shutter speed, and
utilizes light reflected from the surface of a film to control the shutter to
an intermediate or a lower shutter speed.
US3994001: Photometric apparatus for single lens reflex camera
Nov. 23, 1976 / Sept. 13, 1974 (OTF/ Maitani/Olympus)
What is claimed is:
1. A photometric apparatus for a single lens reflex camera and of the type in
which an exposure value is determined by photometry of light which is
transmitted through a photographic optical system and reflected by at least
one of the surfaces of a shutter blind and a film, comprising a photoelectric
transducer element for receiving reflected light from at least one of the
surfaces of a shutter blind and the film;
US4064517: Photometric apparatus for single lens reflex camera
Dec. 20, 1977 / Aug. 24, 1976
A photometric apparatus for single lens reflex camera and of the type in
which an exposure value is determined by photometry of light which is
transmitted through a photographic optical system and is reflected by at
least one of the surfaces of a shutter blind and a film, said apparatus
comprising a photoelectric transducer element for receiving light reflected
by at least one of the surfaces of a shutter blind and a film, and an
operational amplifier for biasing the photoelectric transducer element to
maintain the voltage applied thereacross substantially null, thereby enabling
a photometric output of the photoelectric transducer element to be
effectively derived even when the amount of light received is minimal. The
photometric apparatus, including a photoelectric transducer element, a
photometry switch and associated circuitry are mounted upon a printed circuit
board mounted within the camera to position the transducer element to receive
reflected light from the film or the shutter.
US4072961: Light measuring circuit for automatic exposure control
Feb. 7, 1978 / Aug. 5, 1976 ( Minolta)
Light measuring circuit for camera automatic exposure control measures scene
light passing through the objective and reflected at the film surface and/or
the shutter curtain surface located at the exposre aperture of the camera.
The measuring circuit is provided with a compensating circuit for
compensating the light responsive output for the difference of light
reflecting power of the surfaces of the film and the shutter curtain. The
compensating circuit is actuated in a predetermined timing relationship with
the travel of a shutter curtain.
US4295720: Apparatus for determining light reflection from a focal plane
shutter
Oct. 20, 1981 / Jan. 7, 1980 (Olympus)
An apparatus for determining the amount of light reflected from a focal plane
shutter includes a photoelectric transducer element which determines light
reflection from the shutter blind surface and the film surface. The
transducer element produces a photocurrent which charges an integrating
capacitor. A correcting capacitor is disposed so as to be connected in
parallel with the integrating capacitor during a part of the exposure time in
order to correct the output voltage thereof for different reflectivities of
the film surface and the shutter blind surface. The correcting capacitor is
charged to the same voltage as that appearing across the integrating
capacitor at the time the correcting capacitor is connected in parallel with
the integrating capacitor.
US4459007: Apparatus for reflection photometry of a single lens reflex camera
July 10, 1984 / June 7, 1982
( Olympus)
An apparatus for reflection photometry of a single lens reflex camera
includes a first shutter blind, the surface of which exhibits a reflectivity
which is nearly one-half the reflectivity of a film surface. During the time
a photoelectric transducer element, used for photometry, receives light
reflection from the surface of the first blind, an output from a photometric
circuit is doubled so as to be substantially equal to the output produced
when the transducer element receives light reflection from the film surface
during the running of the first blind.
US4367022: Exposure control circuit for camera of TTL reflective photometry
type
Jan. 4, 1983 / Jan. 25, 1982
(Olympus )
An exposure control circuit for camera of TTL reflective photometry type
includes a shutter blind of a lower reflectivity than that of a film. The
circuit is arranged such that until a given proportion of the film surface
becomes exposed as a result of running of a first shutter blind, a correction
semiconductor element is rendered conductive to supply a current, which
represents a magnified version of minimal current from a photoelectric
transducer element when reflected light from the surface of a first blind is
incident on the transducer element, the current being supplied to an
integrating operation. However, after the given proportion of the film
surface has been exposed to increase the magnitude of the photocurrent, the
correction semiconductor element is rendered non-conductive, thus allowing an
integrating operation of only the photocurrent.
US5184174: Photographic system with off-the-film exposure metering
Feb. 2, 1993 / Nov. 19, 1991 (Kodak)
Off-the-film metering in a photographic film camera is improved by measuring
actual film reflectivity at the time of film manufacture and recording a film
adjusted exposure constant on a magnetic recording layer on the film. Camera
apparatus is provided to read this film adjusted exposure constant value and
generate an adjustable reference level representative of actual film
reflectivity which is then used in confunction off-the-film metering
apparatus to control exposure of the film in accordance with actual film
reflectivity values rather than a fixed or assumed value. Measured film
exposure aim may also be recorded at film production and used to control film
exposure in the camera.
Tim Hughes
Hi100@xxxxxxx
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