1897 PHOTOMETRE J. Decoudun Extinction Meter in Original Box

Description

1897 PHOTOMETRE J. Decoudun Extinction Meter in original box.  "Decoudun's 1897 meter was placed against the camera's focusing screen; the photographer had his head under a black cloth.  A knob on the other side of the meter was turned until the three small holes (a) disappeared, while the larger hole (b) remained visible.  The letter that had then appeared in the window (c) could be referred to on a chart." (See diagrams)
Shipped USPS First Class Mail