Optical calibration device with case and cleaning cloth, neutral density contrast gauge, Bakelite / glass / rubber / cotton, made by Casella London for Air Ministry Meteorological Office, England, c.1940s
Neutral density contrast gauge
A test instrument with a graded neutral density filter mounted in a slide out support with grade markings on the side. The eyepiece has blocked and open sections. Made in black Bakelite in purpose built wooden box.
Mfr: Casella, London (makers of meteorological and photogrammetry and dust measuring instruments)
Has Air Ministry, Meteorological Office ticket marked "For Use in Test Laboratory", dated 27 Nov 1946.