A short excerpt from "Convertible lenses" pag 334 … Jamin had to resort to a particularly elaborate procedure involving five steps: 1) the lens hood was unscrewed and removed. 2) the locking screws on the central barrel were loosened, and the front half of the lens was removed: a sort of cylindrical, black cup, which had an achromatic lens on one side and a Wascher diaphragm on the other. 3) The rear conical part of the lens was unscrewed and removed from…(continue)
MILLET 1861 Centralizing cone N° 1456 ALEXIS MILLET Opticien B.té S.G.D.G. 160 r. St. Martin PARIS. 23x13 cm.
A short excerpt from "Convertible lenses" pag 340: … …His lens is an example of a centralizing cone from 1861 when he was in partnership with the photograph E. Auzou. He was the first to insert the cone inside the cylindrical barrel. Three years after Jamin presented his Objectif double à cone centralisateur in 1857, the optician Millet, presented …(continue)
Derogy's Objectif à foyers multiples et lentilles addictionelles
A short excerpt from "Convertible lenses" pag 343: … Derogy’s L'Objectif à foyers multiples et lentilles addictionelles was introduced in 1858 as a new development, with greater potential than the convertibles developed by Millet and Hermagis. It wasn't only a convertible lens for portraits and landscapes, but was …(continue)

A short excerpt from "Convertible lenses"

Pag 326…For this reason, the first portrait lenses were received with great anticipation: they were three and four times as fast as the simple achromatic landscape lenses which preceded them, and they could produce sharp images even of subjects that did not hold completely still; nevertheless, portrait lenses had a rather restricted field of view, which didn't limit the photographer in the case of an individual portrait, but did limit him when photographing groups or interiors. In an attempt to find a solution for the obstacles photographers faced both indoors and out, convertible lenses like Chevalier's were invented. …(continue)

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