- Subject
- Photography
- Item type
- Object
- Makers
- Francis Watkins
- Provenance
- Lent by the Royal Microscopical Society with their collection. Presented to the society by Mrs C. Evan-Thomas, 19 March 1952.
- Primary inscriptions
- "Watkins Exposure Meter Patent Sole Makers, R. Field & Co. Birmingham" is engraved on the top of the cylinder.
- Dimensions
- Diameter: 40mm Height: 63mm Weight: 105g
- Inventory No
- 85576
Description
A brass copper alloy "tintmeter" where the time is measured for a piece of photosensitive paper to darken to a standard tint when exposed to light falling on the subject. The exposure is then found from the rotary calculator. The
actinic paper is in the form of a disc (none present) that is placed behind a blue glass at one end; this is called the actinometer. The other end has a pull off cap attached to the cylinder by a chain (250 mm) which forms a half-second pendulum to time the darkening of the paper. The calculator has indicators marked: P, D, A, E, standing for: speed of plate, diaphragm f stop, light and enlarging. The Watkins "Standard" exposure meter was patented in 1890 (No. 1388) by A Watkins of Hereford.
