66 J. Watcrhouse — The Application of PJiotof/ra^^li/ [1^0.2, 



The apparatus for supporting the plans varies according to the 

 nature of the work required, and may either be a perfectly smooth board 

 fixed permanently in a truly vertical position against a wall or other 

 support, a form which is very suitable when large plans have to be copied 

 or reduced ; or it may consist of a frame large enough to take a certain 

 size of map and capable of being adjusted in various ways so as to move 

 up and down in a vertical plane or horizontally right and left, so that 

 different parts of the plan may be brought in front of the camera without 

 moving the plan on the board.* In any case, arrangements must exist, 

 either in the plan-board or in the camera-stand, for making the plane of the 

 map or plan to be copied exactly parallel to the plane of the sensitive plate 

 in the camera. 



The map must be attached to the plan -board so that it may lie per- 

 fectly flat and free from ridges. This is best secured by placing in front 

 of it a sheet of glass which is fastened down on the board with pins at 

 the corners. Or a glazed frame may be used for holding plans of a medium 

 size. In either of these cases care must be taken to avoid any reflection 

 from light objects in front of the plan-board. 



It is convenient to have the plan-board and the focussing glass of the 

 camera ruled in squares of 1 inch or other convenient size, in order to at 

 once test the perfect parallelism of the sensitive plate and the plan-board. 



When the work is confined to the reproduction or reduction of maps 

 or other subjects of one fixed size on a single plate, it will be found 

 convenient to draw a rectangle of the required size on the ground glass of 

 the camera. When the image of the subject exactly fills this rectangle the 

 adjustments of focus and parallelism will be correct. 



The camera used for reproduction to scale should be at least of suffi- 

 cient length to draw out to twice the equivalent focal length of the largest 

 lens it is to be used with, and may be furnished with cone fronts to give 

 further extension if necessary. With large cameras of along range of focus 

 it will be found convenient to have the back part of the camera fixed and 

 the front part carrying the lens moveable, so as to enable the operator to 

 focus conveniently. The camera may be fixed on a stand furnished with 

 adjustments for moving it horizontally right or left, and have a tilting mo- 

 tion up and down, in order to adjust the camera perfectly level, or tilt it 

 slightly so as to correct any want of verticality of the plan-board. The 

 camera-stand should run upon rails fixed in the ground at right angles to 

 the wall carrying the plan-board, thus enabling the distance of the camera 

 from the plan-board to be easily and accurately adjusted according to 

 the scale required. When using a reversing mirror or prism for taking re- 



* See my ' Report on the Cartographic Applications of Photography,' plates V, VII 

 and X, and Sir H. James' ' Photozincography', plates I and II. 



