Snelling, Henry Hunt, 1816-1897 · [New York : W.B. Smith] · leaf 94
o the con-clusion, that the most active lenses werethose in which the photogenic focus was themost separated from the visual focus; butwe had no demonstrable proof that theeffect was a consequence of such a theory.This has induced me to endeavor to findsome means by whch the power of lenseshaving… … I shall now proceed to describe the instru-ment which I call a Dijniclinometer^ (fig.7. )itsobject being generally to measure theactinic power resulting both from the in-tensity of the luminous radiation and fiomthe construction of lenses. It consists of athin metallic disc, perfectly black,…
Photography · Art and photography
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