390 



KNOWLEDGE. 



OCTOlil.R, 1911. 



detail. I have never found a ball and socket top to 

 the stand sufficiently rigid and have al\va\-s had to 

 use a tilting table. It is 

 imjiortant that this part . __ 

 of the apparatus shall be 

 firm for small degrees of 

 tilting as well as large, 

 otherwise, w hen the dark 

 slide is introduced, the 

 whole- thing slips, and 

 the photograph obtained 

 is not what was intended. 

 To achieve this, it is essen- 

 tial that the locking screw 

 (A, Figures 2 and 3) be 

 as near as possible to 

 attachment screw (B) when 



the tilting board is closed. 

 The tilting table should 

 open to a right angle 

 so that the camera may 

 look vertically down when 

 photographing tiny jilants. 

 Another essential is that 

 the whole camera should 

 slide backward and for- 

 ward on the tilting board. 

 Suppose, for e.xample, that 

 we are photograjjhing a 

 plant, say natural size, 

 with the camera looking 

 obli(|uel\' down upon it. 

 and have found a suitable 



view on our focussing screen, and proceed to focus. 

 If we do this in the ordinar\- wav, bv backward 

 or forward move- 

 ment of the lens 

 or focussing screen, 

 the scale changes 

 at once and we 

 find that the flower 

 has enlarged itself 

 to, perhai)S, twice 

 its natural size 

 before it is sharplv 

 in focus. If. on 

 the other hand. 

 we attempt to 

 o1)tain correct de- 

 finition by moving 

 the camera and 

 its stand back- 

 ward and forward 

 along the ground 

 we either find that 

 this is exceedingl)- 

 difficult owing to 

 the sloping bank 

 on which the 

 plant grows or to 

 or else that, owing 

 camera, the point 



FlGUKlC 2. 

 The Half-plate Field Camera. 



as we advance and recede, the object falls and 

 rises on the focussing screen. It is much more 



con\enient to focus by 

 sliding the whole camera 

 backward and forward on 

 the tilting board and fixing 

 it by a locking screw iC. 

 Figures 2 and 5) before 

 exposure. The tilting board 

 on which my half-plate 

 field camera slides has 

 narrow brass strips on top 

 which engage with similar 

 brass strips screwed to 

 the base of the camera. 

 There is nothing striking 

 about the little pieces of 

 apparatus w hich I ha\'e had 

 made to attach to the bases 

 of mv two field cameras, 

 but as a diagram mav per- 

 haps be of service to some 

 reader. I ha\e thought 

 best to include one with 

 dimensions marked upon it. 

 The half- plate size is here 

 figured and the quarter- 

 plate is \"ery similar, ex- 

 cept that the part of the 

 tilting board which is 

 nearest to the camera is 

 formed of an aluminium 

 instead of wood, 

 hapjiens. the camera 

 instead of down, it 



plate 

 Where, as very occasionalh' 

 has to be directed upward 



is the easiest thing 

 in the world to 

 slide theinstrument 

 off the tilting base 

 and reverse it so 

 that the lens points 

 upward, before re- 

 placing it. 



The Stand. 



There can be no 

 possible doubt that 

 the telescopic is b\- 

 far the most con- 

 venient t\'pe of 

 stand for work in 

 the field. It is easih' 

 carried and adjus- 

 ted, and one of the" 

 better ty[)es with 

 six or se\en sec- 

 tions to each leg 

 permits of the close 

 ajiproximation of 

 rocks or other ol)structions, the camera to the ground in photographing small 

 to the tilted position of the plants. It is rigid enough even with a half plate 

 of \iew entirelv changes, for camera, and is very rarely used fulK" extended. 



The tilting base on whicl 



FiGiKi; 3. 

 the Camera slides backwards and forwards. 



