Photoelectric exposure meters

Claim 2

For a photoelectric exposure meter comprising a first casing having a first light entry aperture in a wall thereof, attachment holding means in the vicinity of the said first light entry aperture, a first photosensitive device located within said casing for exposure to light entering through said first light entry aperture, an electrical measuring instrument calibrated in light or equivalent photographic values, electric circuit means connecting said measuring instrument with said first photosensitive device to be energized by a current which varies in amplitude in accordance with the degree of illumination of said first photosensitive device by light entering said first light entry aperture and external electric connector means on said casing and connecting to said electrical measuring instrument, the improvement comprising an attachment for extending the measurement range of said meter to light values of lower intensity, which attachment comprises a second casing having a second light entry aperture in a wall thereof, a second photosensitive device located within said second casing for exposure to light entering through such second light entry aperture, external electrical connector means connected to said second photosensitive device and attachment means for cooperating with said attachment holding means on said first casing to hold said attachment in a position which closes said first light entry aperture against the passage of light therethrough onto such first photosensitive device and with said external electric connector means cooperating with the external electrical connector means of said first casing to connect said second photosensitive device to said electrical measuring instrument in an electric circuit by means of which said measuring instrument is energized in accordance only with the degree of illumination of said second photosensitive device.

Claim 3

An arrangement for measuring a plurality of different ranges of light intensity values which comprises a photoelectric exposure meter including a first casing having a first light entry aperture in a wall thereof, a first photosensitive device located within said casing for exposure to light entering through said light entry aperture, an electrical measuring instrument calibrated in light or equivalent photographic values, electric circuit means connecting said measuring instrument with such first photosensitive device to cause energization of such measuring instrument by a current which varies in amplitude in accordance with the degree of illumination of said first photosensitive device by light entering said light entry aperture, attachment holding means on said first casing in the vicinity of said first light entry aperture and external electric connector means electrically connected to said electrical measuring instrument and an attachment arranged for deTachable mounting on said first casing and comprising a second photosensitive device, attachment means cooperating with said attachment holding means of said first casing to secure said attachment to said first casing in a position completely obscuring said first light entry aperture from the entry of light therethrough onto said first photosensitive device and external electric connector means cooperating with said external electric connector means connecting said second photosensitive device into the circuit of said electrical measuring instrument whereby said measuring instrument is energized solely in accordance with the illumination incident upon said second photosensitive device when said attachment is in position and whereby said measuring instrument is energized only in accordance with the degree of illumination incident upon said first photosensitive device when said attachment is removed from said meter.

Claim 4

An arrangement for measuring a plurality of different ranges of light intensity values which comprises a photoelectric exposure meter including a first casing having a first light entry aperture in a wall thereof, a first photosensitive device located within said casing for exposure to light entering through said light entry aperture, an electrical measuring instrument calibrated in light or equivalent photographic values, electric circuit means connecting said measuring instrument with such first photosensitive device to cause energization of such measuring instrument by a current which varies in amplitude in accordance with the degree of illumination of said first photosensitive device by light entering said light entry aperture, attachment holding means on said first casing in the vicinity of said first light entry aperture and external electric connector means electrically connected to said electrical measuring instrument and an attachment arranged for deTachable mounting on said first casing and comprising a second photosensitive device, attachment means cooperating with said attachment holding means of said first casing to secure said attachment to said first casing in a position completely obscuring said first light entry aperture from the entry of light therethrough onto said first photosensitive device and external electric connector means cooperating with said external electric connector means connecting said second photosensitive device into the circuit of said electrical measuring instrument whereby said measuring instrument is energized solely in accordance with the illumination incident upon said second photosensitive device when said attachment is in position and whereby said measuring instrument is energized only in accordance with the degree of illumination incident upon said first photosensitive device when said attachment is removed from said meter.

Claim 5

An attachment according to claim 1 in which said second photosensitive device is of the photoresistive type and in which said attachment also carries a current source.

Claim 6

An attachment in accordance with claim 3 in which said second photosensitive device is a cadmium sulfide cell.

Claim 7

An attachment in accordance with claim 3 in which said attachment includes manually operable switch means by which said current source may be connected into operative circuit relationship with said second photosensitive device, disconnected or connected into a voltage test circuit which includes said electrical measuring instrument.

Claim 8

An attachment according to claim 1 which includes a transistor current amplifier for amplifying the output from said second photosensitive device.

Claim 9

An attachment according to claim 1 which carries an exposure calculator mechanism for dealing with the additional illumination measurement range provided thereby.

Claim 10

An attachment according to claim 1 in which said attachment holding means on said first casing and said attachment means on said second casing comprise a bayonet-type coupling.

Claim 11

An attachment according to claim 8 in which said bayonet-type coupling includes projecting metal parts which serve also as said external electric connector means on said first and second casings.

Claim 12

An arrangement according to claim 2 in which said second photosensitive device is of the photoresistive type and in which said attachment also includes a current source.

Claim 13

An arrangement according to claim 10 in which said second photosensitive device is a cadmium sulfide cell.

Claim 14

An arrangement according to claim 10 in which said attachment includes manually operable switch means for connecting and disconnecting said current source into and from operative circuit relationship with said second photosensitive device and for connecting such current source into a voltage test circuit which includes said electrical measuring instrument.

Claim 15

An arrangement according to claim 2 in which said attachment comprises a transistor current amplifier operative to amplify the output from said second photosensitive device.

Claim 16

An arrangement according to claim 2 in which said attachment comprises an exposure calculator mechanism for dealing with the additional illumination measurement range provided thereby.

Claim 17

An arrangement according to claim 2 in which said attachment holding means on said first casing and said attachment means on said second casing comprise a bayonet-type coupling.

Claim 18

An arrangement according to claim 15 in which said bayonet-type coupling includes cooperating metal parts which serve also as said external electric connector means on said first and second casings.

Claim 19

An arrangement according to claim 16 in which the operative circuit within said exposure meter is altered when said attachment is applied thereto and in which the application of said attachment is arranged automatically to effect the necessary circuit alteration.

Claim 20

An arrangement according to claim 17 in which the required circuit alteratiOn is effected by bridging at least two contacts of said external electric connector means of said exposure meter with one of said bayonet-type connector members.