Exposure control device for camera

Claim 2

An exposure control device for a camera comprising: at least three read contacts for reading film speed information indicated on a film cartridge in the form of a binary code comprising at least three digits; an adjustable reference voltage setting circuit including at least three automatic presetting resistors having their one end connected to a separate one of the at least three read contacts for developing at their other ends, which are connected in common, a reference voltage in accordance with the film speed information which causes the read contacts to be selectively turned on and off for use in the decision of an exposure level; a photometric circuit for generating an output signal which is a function of the photoelectric conversion coefficient γ c of the photometric circuit; a comparator having a first input to which said other end of the at least three resistors is connected in common and a second input to which the output of the photometric circuit is directly connected; and an exposure controlling member operative in response to an output signal from the comparator, the value of the photoelectric conversion coefficient γ c being chosen so that the reference voltage app1ied to the first input of the comparator for more than four different values of film speed which are spaced apart at least by 1 EV are kept with in a permissible range of exposure errors so that the magnitude of the exposure errors is minimized; at least three of the read contacts which are used to read the three most significant digits of the binary code being allocated to read typical film speeds, each of such contacts and an associated resistor being connected in series between the first input of the comparator and the ground, whereby when a plurality of read contacts are turned on, a composite resistance formed by a parallel combination of the resistors which are connected to those contacts which are turned on define a reference voltage applied to the first input in accordance with the particular value of film speed designated by the film cartridge.

Claim 3

An exposure control device according to claim 1 in which there are three automatic presetting resistors having resistances which are chosen in the ratio of 1:2 - γ.sbsp.c :2 -3 γ.sbsp.c.

Claim 4

An exposure control device according to claim 1 in which there are three automatic presetting resistors having resistances which are chosen in the ratio of 2 -4 γ.sbsp.c /(1-2 - γ.sbsp.c):2 - γ.sbsp.c :2 -3 γ.sbsp.c.

Claim 5

An exposure control device according to claim 1 in which one of the at least three read contacts which is allocated to read a digit which is less significant than the three most significant digits of the binary code is adapted to detect that a film cartridge carrying a binary code is loaded into a camera, the device including a manual presetting circuit comprising a plurality of manual presetting resistors having their one end connected to the first input of the comparator, and a changeover switch for manually selecting one of the manual presetting resistors, the device also including an automatic selection circuit including said one contact and a switching circuit which enables or disables the manual presetting circuit when said one contact is turned on or off, respectively.

Claim 6

An exposure control device according to claim 4 in which the plurality of manual presetting resistors have resistances which are chosen to change from one to the next by a factor of 2 - γ.sbsp.c, for each change in film speed of 1 EV, as referenced to a selected resistance which corresponds to a particular film speed.

Claim 7

An exposure control device according to claim 1 in which the photometric circuit includes a light receiving element in the form of a photoelectric transducer element as may be formed by a cadmium sulfide (CdS) element, the transducer element determining the value of the photoelectric conversion coefficient γ c .

Claim 8

An exposure control device according to claim 1 in which the photometric circuit includes a light receiving element in the form of a photoelectric transducer element as may be formed by a silicon photodiode, the output of the transducer element being connected to a voltage divider, the division ratio of which determines the photoelectric conversion coefficient γ c .

Claim 9

An exposure control device according to claim 7 in which the voltage divider is adjustable to adjust the output of the photometric circuit applied to the comparator.

Claim 10

An exposure control device according to claim 7 in which the photometric circuit includes a charging capacitor which is charged at a rate determined by the silicon photodiode; said voltage divider being comprised of series connected resistors receiving the current output of the silicon photodiode, the charging capacitor being coupled to the common terminal therebetween; one of said series connected resistors being adjustable for adjusting the photoelectric conversion coefficient in order to maintain the aforesaid exposure errors within the aforementioned permissible range.

Claim 11

An exposure control device according to claim 1 in which the exposure controlling member comprises an electromagnet which controls the operation of a shutter.

Claim 12

An exposure control device according to claim 1 wherein the value of the coefficient γ c is selected so that the preferred range of error ΔEV is -1 EV≦ΔEV≦+1 EV.

Claim 13

An exposure control device according to claim 11 wherein the preferred range of ΔEV is -2/3 EV≦ΔEV≦+2/3 EV.

Claim 14

An exposure control device according to claim 1 in which the output of the photometric circuit is logarithmically compressed by logarithmic compression means before application to the comparator, while the output of said adjustable reference voltage setting circuit is directly applied to said comparator without undergoing logarithmic compression.

Claim 15

A logarithmic conversion circuit according to claim 1 further including a manually adjustable reference voltage setting circuit having a plurality of resistors each having one end connected in common to an output terminal coupled to the common connection of said adjustable reference voltage setting circuit; electronic switch means; manually operable switch means, for selectively coupling one of the resistors in said manually adjustable reference voltage setting circuit to said electronic switch means; means responsive to the presence of a film cartridge having binary coded film speed information provided thereon for deactivating said electronic switch and for activating said electronic switch when the film cartridge has no binary coded film speed information provided thereon so as to selectively connect only one of said automatic and manual reference voltage setting circuits to said comparator.

Claim 16

An exposure control device according to claim 1 wherein said photometric conversion circuit further includes a photometry element; means for logarithmically compressing the output of the photometry element; voltage divider means for adjusting the logarithmically compressed photometric element signal; and means for coupling the adjusted output of the voltage divider means to said comparator, said voltage divider means being adjusted to adjust the photometric conversion coefficient of the photometric circuit.

Claim 17

An exposure control device according to claim 1 wherein the decision voltage levels generated by the voltage setting circuit are greater in number then the number of presetting resistors.

Claim 18

An exposure control device for a camera comprising: at least three read contacts for reading film speed information indicated on a film cartridge in the form of a binary code comprising at least three digits; a switching element which is turned on as a film cartridge carrying a binary code is loaded into the camera; at least four automatic presetting resistors having their one end connected to the switching element and to that least three read contacts for developing at their other ends, which are connected in common, a reference voltage in accordance with a film speed read from the film cartridge which causes the contacts to be selectively turned on and off, for use in the decision of an exposure level; a photometric circuit for generating an output signal which is a function of the photoelectric conversion coefficient γ c of the photometric circuit; a comparator having a first input to which the other end of the at least four resistors is connected and a second input to which the output of the photometric circuit is connected; an exposure controlling member operative in response to an output signal from the comparator, the value of the photoelectric conversion coefficient γ c being chosen so that each of the reference voltages applied to the first input of the comparator for five or more values of film speed which are separated apart by at least 1 EV be kept within a permissible range of exposure errors so that the magnitude of the exposure errors is minimized; and at least three of the read contacts which are associated with the three most significant digits of the binary code are allocated to read typical film speeds (ISO 50, 100 and 400), each of the switching elements and the read contacts being connected in series with an associated automatic presetting resistor between the first input of the comparator and the ground so that when a plurality of read contacts are turned on, a composite resistance formed by a parallel combination of automatic presetting resistors which are connected to the switching element and those read contacts which are turned on establishes a reference voltage applied to the first input in accordance with the particular value of film speed.

Claim 19

An exposure control device for a camera comprising: at least three read contacts for reading film speed information indicated on a film cartridge in the form of a binary code comprising at least three digits; a switching element which is turned on as a film cartridge carrying a binary code is loaded into the camera; at least four automatic presetting resistors having their one end connected to the switching element and to that least three read contacts for developing at their other ends, which are connected in common, a reference voltage in accordance with a film speed read from the film cartridge which causes the contacts to be selectively turned on and off, for use in the decision of an exposure level; a photometric circuit for generating an output signal which is a function of the photoelectric conversion coefficient γ c of the photometric circuit; a comparator having a first input to which the other end of the at least four resistors is connected and a second input to which the output of the photometric circuit is connected; an exposure controlling member operative in response to an output signal from the comparator, the value of the photoelectric conversion coefficient γ c being chosen so that each of the reference voltages applied to the first input of the comparator for five or more values of film speed which are separated apart by at least 1 EV be kept within a permissible range of exposure errors so that the magnitude of the exposure errors is minimized; and at least three of the read contacts which are associated with the three most significant digits of the binary code are allocated to read typical film speeds (ISO 50, 100 and 400), each of the switching elements and the read contacts being connected in series with an associated automatic presetting resistor between the first input of the comparator and the ground so that when a plurality of read contacts are turned on, a composite resistance formed by a parallel combination of automatic presetting resistors which are connected to the switching element and those read contacts which are turned on establishes a reference voltage applied to the first input in accordance with the particular value of film speed.

Claim 20

An exposure control device according to claim 17 in which the switching element is formed by a transistor which is turned on in response to the closure of a contact which is allocated to detect the loading of a film cartridge carrying a binary code.

Claim 21

An exposure control device according to claim 10 in which the automatic presetting resistors connected to the switching element and the read contacts have resistances which are chosen in the ratio of ##EQU36##