A manual of photographic chemistry, theoretical and practical . d glass, and accurately coincides with a pencil linemade thereon. JMow, with a pencil draw a line on the paperbeneath the camera, parallel with one side of the latter ; turnthe camera round until the object at the other extremity ofthe subject coincides with the pencil line on the focusingscreen, and draw another line on the paper as before. Theangle formed by the two lines thus drawn will show theangle of picture included. But this is not all ; for if wedraw a line opposite to the angle thus formed, at such a dis- APPENDIX. 36d t
A manual of photographic chemistry, theoretical and practical . d glass, and accurately coincides with a pencil linemade thereon. JMow, with a pencil draw a line on the paperbeneath the camera, parallel with one side of the latter ; turnthe camera round until the object at the other extremity ofthe subject coincides with the pencil line on the focusingscreen, and draw another line on the paper as before. Theangle formed by the two lines thus drawn will show theangle of picture included. But this is not all ; for if wedraw a line opposite to the angle thus formed, at such a dis- APPENDIX. 36d tance therefromassliall allow the third line, bounded by thetwo previous^ones/^to^be of the same length as the focusingscreen, a perpendicular let fall from the angle upon the thirdline will give the equivalent focal length of the lens equivalent focal distance may or may not agree with thedistance of the screen from the lens—most probably not, es-pecially if it be a double combination. To simplify this matter, we append the following diagram:. Fig. 57. Let A B represent a moderatelj distant view, and C theplace of the camera. On focusing, we find the portion in-cluded on the ground glass to be from D to E only; this isthe angle of picture. If we now turn the camera towards D,so as to make its image fall on a line in the center of thefocusing screen, and draw a line parallel with the side of thecamera, we shall have a line parallel to C D. viz., c d. Onturning the camera towards E, and making its image fall onthe same mark on the screen, another line drawn parallel withthe same side of the camera will also be parallel with C E,viz., G e, and these two lines are inclined to one another ex-actly in the same ratio as are C D and C E. By measurement upon the ground glass, we find the dis-tance between the images of the objects D and E to be equalto g h • and if we now place this line exactly opposite the an-gle G, SO as to be bounded by the lines g d, g e, and let
Size: 1661px × 1505px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookidma, booksubjectphotography
