Novi;mber. 1911. 



KNOWLEDGE. 



447 



holdini; a camera vertically over such a small object as a 

 flower. This is laid on a sheet of gray non-shiny, but not very 

 rough, paper, and supported at a convenient height above the 

 floor b\- a box. pile of books, and so on. The camera is held 

 in the position shown by tying the tripod legs to the top rails 

 of two chairs. 1 he sheet of white cardboard on edge between 

 the box and chair is used as a reflector to prevent the object 

 casting too dark and detail-less shadows. This method also 

 serves conveniently for copying maps, plans, diagrams, and so 

 on, in books. The photographic reader will scarcely need to 

 be told that to copy "same size" the lens will have to be at 

 double its focal length from the ground glass, and also this 

 same distance from the object. 



To find the lens-to-image distance for any magnification, 

 e.g.. 4 times, we add 1 to 4 getting 5 and multiply this by the 

 focal length. Thus with a ft-inch lens and J diameters 

 magnification the lens to image distance is 3 plus 1 times 6. 

 or 24 inches. While the leits to object distance is one third 

 of 24 or 8 inches. It will thus be seen that in this field of 

 work our limit of magnification depends on the relationship of 

 focal length of lens to camera bellows length. Thus to find 

 the greatest magnification with a 12-inch bellows and 4-inch 



U is a loose piece which slips over the top of the upright par 

 E, and it forms a shelf (Figure 3). These two nioxing 

 pieces are made out of the wood of an old cigar box, and cigar 

 box nails. 



i- II .L KI-. 1. 



lens we divide 12 by 4 and get J. Then subtracting 1 we get 

 2, or the maximum magnification \\ith a 4-inch lens and 

 12-inch camera bellows is 2 times i.e. double life size. 

 Finally, requiring to know what lens will give us 10 diameters 

 magnification with a 24-inch camera bellows we add 1 to 10 

 getting 11, and then divide 24 by 11 getting 2rr, as the 

 maximum focal length, so that to be on the working side we 

 should limit our focal length to 2 inches. The above scraps 

 of simple arithmetic must be kept in mind whenever we are 

 fitting up home-made contrivances of the sort to be herein 

 below mentioned. 



I now turn to an easily-made apparatus (Figure 21 that I 

 have had in use for many years with complete satisfaction. 

 It is especially well adapted for small objects, e.g.. shells, 

 fossils, seeds, and so on, which can be stuck to a card, or 

 small enough to rest on a quite narrow (half-inch i shelf. 



F~igure 2. — A, the top of an ordinary tripod stand. The 

 camera screen is attached to the under-side of the triangular 

 top by means of a cheap steel watch chain with swivel end. 

 which engages with a ring passing through the pierced head of 

 the camera screw. This prevents the camera screw from being 

 lost. BB a straight grain piece of (teak) wood, say three feet 

 long by four inches wide by half-an-inch thick, which acts as an 

 extension and base board. The camera screw passes through 

 its usual hole in the tripod top, then through a hole in BB, 

 and finally enters the " bush " let into the base of the camera. 

 These three parts now become as one solid piece on tightening 

 the screw. CE is a loose piece (see Figures 3 and 4) 

 which slides along BB. 



F'IGIIRE 2. 



At F we see the plate end of the camera, but the re\ersing 

 back and focussing screen have been removed, so that we 

 may see a contrivance which enables ns to use the right and 

 left-hand halves of a quarter-plate for two different pictures. 

 This effects economy of material (cost), time, and storage 

 space when we are — as is often the case — concerned with 

 images which occupy only a small fraction of a qnarter-plate. 

 (The two figures 3 and 4 were thus taken side by side on one 

 ipiarter-platel. The contrivance consists of a piece of card- 

 board, blackened on both sides. It is of such a size that one 

 can bend and spring it into the last groove of the camera 

 bellows just inside the camera body. When it is pushed as 

 far as it will go to one side, it is just big enough to obscure 

 half the focussing screen, so that when pushed to the other 

 side it similarly obscures the other half. The procedure 

 is: (1) push the card to right; (2) focus on the left half of 

 screen ; (3) insert the plate holder, expose, close the slide and 

 withdraw it from the camera ; (41 push the card to the opposite 

 side ; (5) focus on the other half of the screen for the second 

 picture ; (6) insert the plate holder, expose, close and withdraw 

 it. and so on. We have now two image exposures on the plate- 

 side by side. 



I'IGIIRE 3. 



•'u.UKi': 4. 



Figures 3 and 4 show the two sides (front and back) of the 

 sliding object holder. Figure 3 shows the shelf, I), slipped over 

 the upright part, E, and held in place by a drawing pin below 

 D. A small shell rests on a piece of paper to serve as a back- 

 ground, G. Figure 4 shows a small shell stuck to a piece of 

 card which is held in place by a drawing pin, H. At K we 



