142. Heyde's Aktinophotometer, c. 1905
Signed: 'HEYDES / AKTINO / PHOTO / METER'
An improved version of the optical exposure meter in which the designer has attempted to reduce the effect of pupil dilation of the eye due to weak illumination by making the eyepiece aperture smaller than the minimum pupil diameter of the eye.
Diameter 59 mm, depth 15 mm.
Inventory no. 75,125.