“Hoh & Hahne”

Data:

• The slide rule was probably made by Nestler, because the paper on the back is the same as on Nestler types.
  The black label hides the text “Albert Nestker Lahr i.B.” without “A.G.”, which indicates the slide rule is made before 1922.
  The 285 mm body is not made from mahogany but from walnut, which features in the 1914 Nestler Catalog Andreas Faßbender
• The cursor has only one line.
• “The company Hoh & Hahne (later known under the brand name HOHLUX) was a historic, now liquidated, manufacturer of photographic equipment and reproduction technology in Leipzig. It no longer exists as an active company.”
  Hoh & Hahne was merged into the VEB Polygraph Reprotechnik in 1962. Andries de Man
  Aristo made a calculating disc for HOHLUX: the Aristo 60115 David Rance
• more images and information (Andreas Faßbender)

Questions:

Animate this slide rule
1. What were the A and B Scales used for?
   They solve the thin lens equation

   1 f

   =

   1 A

   +

   1 B

   with f = focal length (46 cm, as indicated at the far left)
   A = distance from the lens to the photographic plate
   B = distance from the lens to the object
   Try it yourself: set an A or B value and compare the A-B pair with the slide rule.
   A=
   B=
   Note the A-scale runs in a direction opposite the B-scale.
   In Hoh & Hahne camera's the distance between lens and photographic plate was variable. Andries de Man