Patent GB-191405317-A (GB)
Title: Improvements in Copying and Enlarging Cameras.
Inventor: BECKER JOSEPH
IPC: G03B27/68
Filed: 1914-03-02
Granted: 1915-04-06
Abstract: 5317. Becker, J. March 2. Enlarging, copying, and reducing.-Relates to copying or enlarging cameras having the two end frames 0, I, Fig. 2, mounted to turn on parallel diametral axes P, P' perpendicular to and intersecting the principal axis F, F<1> of the lens, and comprises a construction of mechanism which, when the image is once set, compels the two frames O, I to tilt simultaneously towards each other in such a manner as to maintain the image of a figure with converging lines, such as is shown in Fig. 5, and such as is obtained by a tilted camera without a swing back, as a sharp rectified figure as shown in Fig. 6. The apparatus may also be combined with mechanism, such as is described in Specifications 24,292/11 and 29,701/12 for maintaining the object and image frames in focus for different scales of reproduction. The apparatus is based upon the geometric consideration that if in Figs. 4 and 5 V is the vanishing point of the converging lines X E W, R P Q and Z G Y of the figure, and N, N', F, F<1> the nodal points and foci of the lens 99, and P, P' are conjugate points, then the correct angular position for a rectified image R<1>, P<1>, Q' in which the corresponding vanishing point V<1> is at infinity is determined by the equation tan a/tan a<1> = PN/N<1>P<1>, which ratio is constant for the particular scale of reproduction. In one apparatus according to the present invention the frames O, I are tilted by means of slotted arms 403, 403', pins p, p<1> on transverse slides 404, 404<1>, and a lever 410 with slots engaging pins b, b<1> on the slides 404, 404' and pivoted at c on a fixed transverse bar 411. The pin b is spaced at a distance equal to the nodal distance N N' from the central line p H of the slide 404. With this construction it is seen that tan a<1>/tan a = P<1> H<1>/pH = b<1> K<1>/bK = c K<1>/cK = cH<1>/cH-N N<1> Provided therefore c H - N N<1> = N P and c H<1> = N<1> P<1>, i.e., provided P H = c<1> N<1> = P<1> H<1>, the above conditions for rectilinear correction are fulfilled for any angular position of the frames O and I controlled by the lever 410. To determine the position of the arm 411 and c, and to set the apparatus the frames 0, I are placed perpendicular to the optical axis and the slide 410, the frames each focussed on infinity so that the two pairs of points F, P and F<1>, P' coincide, and c is set half way between the pins p, p' which will be on the optical axis. The lever 410 is graduated to facilitate this setting. For any particular scale of reproduction it is only necessary then to fix P and P' as conjugate points by focusing. In a modified construction of apparatus, Fig. 3, the frames O, I pivot on horizontal axes directly tilted by the slotted lever 218 which engages the pins p, p<1>. The pivot c is adjustable towards and away from the lens frame and is determined in the same way as for the former apparatus. The nodal distance N, N' is ignored and the adjustment with this apparatus is only approximate. The apparatus is combined with link-work mechanism 120, 121, 122, 123 such as is described in Specification 24,292/11 for automatically maintaining the focus for various scales of reproduction. The Specification also discusses the value of the distance h<11>, Fig. 4, and various questions arising from and relative advantages in the use of tilting backs and rising fronts. Specifications 1139/01 and 1196/04 also are referred to.