Elements of natural philosophy (Volume 2-3) . e paper, the wholeof which will be seen B through the uncoveredhalf of the pupil, anda picture of the objectmay thus be traced bybringing the pencilin succession in ap-parent contact withits various parts. The linear dimen-sions of the picturewill be to those of theobject, as the distance of the camera from the paper,to its distance from the object, nearly. If the paper be very near, the eye may not havepower to bring the rays proceeding from the pencil tothe same focus with those from the object; this difficultyis obviated by the use of a convex l
Elements of natural philosophy (Volume 2-3) . e paper, the wholeof which will be seen B through the uncoveredhalf of the pupil, anda picture of the objectmay thus be traced bybringing the pencilin succession in ap-parent contact withits various parts. The linear dimen-sions of the picturewill be to those of theobject, as the distance of the camera from the paper,to its distance from the object, nearly. If the paper be very near, the eye may not havepower to bring the rays proceeding from the pencil tothe same focus with those from the object; this difficultyis obviated by the use of a convex lens at Z, or a con-cave one at L ; the effect of the former being to reducethe divergence of the rays from the pencil to the samedegree with that of those from the object, and of thelatter, to increase the divergence of the rays from theobject, and render it the same with that of the rays fromthe pencil. The camera lucida is constructed of variousforms, having reference to the facility of using it, theoptical principle being the same in ELEMENTS OF OPTICS. 263 CAMERA OBSCURA. Used to copyfrom nature; Its essentialparts; § 88. This instrument is also used to copy fromCamera obscura;nature, and like the camera lucida, has variousforms, one of the best of which is represented in thefigure. AB (7 is a prismaticlens, which is nothing more lg than a triangular prism withone or both of its refractingfaces ground to spherical sur-faces ; it is set in a small boxresting on a cylindrical tubetv, that moves freely in asimilar tube in the top of adark chamber, formed by up-rights or legs, about whichis suspended a cotton clothrendered impervious to lightby some opaque size. On oneface of the box ?n n, contain-ing the prismatic lens, is anopening to admit the lightfrom any object in front of the instrument, and on one side the cloth has beenomitted in the figure to show a table X Y, supportedby the uprights, on which the paper is placed to re-ceive the picture. Now, the rays from any
Size: 1694px × 1475px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksubjectmechanics, booksubjectopticsandphoto
