Huyghenian Eye-pieces.
Reading edition
Number 0 I II III IV V
Focal length mm 50 40 35 30 25 20
Price of each eyepiece $ 2.00.
The objectives designed for the Edinger apparatus of 64, 42, 35, and 24 mm focal distance have been found to be very useful for a number of purposes and have come into great favor.
(see. Dr. Kaiserling: Praktikum der wissenschaftlichen Photographie p. 263).