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Photoelectric Exposure Meter
Photographers judged exposure by eye, by printed tables, or with extinction meters that asked them to read the dimmest visible number. Edward Weston (the instrument maker, not the photographer) used a photovoltaic cell that generates its own current in light and fed it straight into a sensitive meter marked in exposure terms. No battery, no judgement.
**US 2,016,469**, "Exposure meter", Weston, assigned to Weston Electrical Instrument, filed 31. December 1931, granted 8. October 1935: an instrument "for the direct determination of the correct exposure conditions", improving on earlier current-generating cell meters whose output was too small and whose construction was impractical.
**You build the same thing** from a small solar cell and a multimeter, calibrate it against a lux meter, and turn its readings into shutter speeds.
Beginner
90 minutes
Instructions
1
1
Cell and meter
Cell and meter
Clip the solar cell's two leads to the multimeter set to DC milliamps (or microamps). This short-circuits the cell through the meter - the current is what you read.
Materials for this step:
Solar Cell Mini - 350mV1 pieceTools needed:
Multimeter
Alligator to Alligator Cables2
2
A hood
A hood
Glue a black card tube 30 mm long around the cell so it sees only light from in front, as Weston's meter did.
Materials for this step:
Black Card Stock1 sheetTools needed:
Craft Knife
Hot Glue Gun3
3
Calibrate
Calibrate
Hold the cell and the lux meter side by side, facing the same way, in four very different lights: a dim room, a lamp, a window, open shade outdoors. Note both readings each time.
Tools needed:
Lux Meter4
4
Current to exposure
Current to exposure
Loading Jupyter Notebook...
5
5
Use it
Use it
Stand at the subject, point the hood back towards the camera, read the current, and set the camera manually from the notebook's table. Compare with the camera's own meter.
Tools needed:
Multimeter6
6
History & Context
History & Context
**What the patent specifies:** a light-sensitive current-generating cell connected to a measuring instrument reading directly in exposure terms. **Modern build (derived):** a silicon solar cell and a multimeter.
Weston's selenium-cell meters, sold from 1932, made metering routine; cameras later built the cell in. Its limits: selenium cells lose sensitivity in dim light and age, and any meter averages the scene - a snowfield or a black cat still fools it.
Materials
2- Solar Cell Mini - 350mV10% commission1 piece$2.22
- 1 sheetPlaceholder
Tools Required
5- Placeholder
- Alligator to Alligator Cables10% commission$3.58
- Placeholder
- Placeholder
- Placeholder
Estimated Total
What the maker bought. Materials shown without a price are sourced wherever you buy them.
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