October. 1911. 



KNOWLEDGE. 



391 



\Miere there has heen a strong wind blow ing I have 



sometimes increased the weight, and therefore the 



rigidity, of my N\hole apparatus by placing a few large 



stones, wherever I could find room for them on the 



camera base. And sometimes 



where the camera and stand are 



much tilted, a few stones piled 



around that leg which has a ten- 



dencv to rise will make the whole 



thing much firmer. If you are 



likelv to use \our camera-stand 



more than once, get a brass or 



steel one and strenuously avoid 



those made of aluminium. 



The Lr-:NS. 

 next to the 



Turnin 

 of the lens I can 

 give you my own 

 perience. I have 



makes but have got 



questiiin 

 again t)nl\- 

 imited ex- 

 tried most 

 rid of all 

 mv lenses, except a Zeiss Tessar, 

 which I use for everything. 

 It is a delightful lens, and of 

 especial value in autochrome 

 work. It is certainly the best I 

 have tried, though it is quite 

 likely that there are others just as 

 good. The right thing to do 

 is clearly to tr\- the lens you 

 have and wait to get another 

 till you are quite certain that your 

 jjresent one is deficient. I prefer 

 a rather short focus lens, for 

 then one can photograph an 

 object natural size \sith the 

 camera somewhat less than doubly 

 extended, and complete double 

 extension gives a slight magnifi- 

 cation. Besides, it is often easier 

 to pitch one's camera quite close 

 to a ])lant than some little distance 

 awa\-, particularly in rocky places. 

 There is no advantage in a wide 

 aperture lens for plant photo- 

 graphy. One working at V 6-5 

 or F 8 is quite good enough, and 

 I never remember photograjihing 

 a plant with a larger stop than 

 F 8. Much more often one has to stoj) down 

 to I*" 24 or :>2 to obtain sufficient depth of 

 focus. Occasionally in the field, and not infre- 

 quentlv in the studio, it may be desirable to 

 photograph a plant or flow er larger than natural size. 

 This can be managed with the hel|) of a triple 

 extension camera, but rigidity is almost invariably 

 lost with the greater degrees of extension, and it is 

 much more convenient to increase the power of the 

 lens by the addition of an ordinary convex objective. 

 I use a simple convex lens placed in front of m\- 

 camera lens. It is a corrected lens, being made up 

 of two glasses cemented together, and is really the 



objective bought w ith a cheap quarter-plate camera. 

 With it I am able to obtain any magnification 

 up to six diameters. Beautiful autochromes as well 

 as ordinar\' photographs can thus be obtained. 



Plates. 



For all ordinary work plates 

 are much to be preferred to 

 films. Backed plates should 

 alwa\s be used, and a colour 

 sensitive plate is essential. 

 Undoubtedly the very best results 

 are obtained with such a plate as 

 the Panchromatic, but these are 

 perhaps a little troublesome to 

 develop, and quite satisfactory 

 pictures can be taken on any 

 of the ordinary colour sensitive 

 plates. I have used Barnet 

 Chromatics for several years, and 

 have no reason to change. There 

 is no point in selecting an exces- 

 sivel\- rapid plate, I'or blue, red 

 or orange flowers a colour screen 

 is, of course, necessary, Init it has 

 to be remembered that the use 

 of a colour screen, even of the 

 palest tint, doubles or quadruples 

 the exposure, and makes the 

 struggle with the worst enem\- 

 of the plant photographer — wind 

 — all the keener. Not infre- 

 quenth'. therefore, the colour 

 screen will be dispensed with, 

 and a fairly satisfactory result 

 obtained nevertheless. Occas- 

 ionalh- also a special point in the 

 picture can be emphasised, or 

 made to stand out more clearly 

 b\' intentionally over- or under- 

 correcting the colour values. For 

 mstance, the yellow stamens of 

 a white flower are more distinctK- 



seen when 

 used, but a 



no 

 vel 



,'ht filter 

 ■ floN 



will 



The (Trecn - winged Meadow Orchis 



[Orchis Moi'io). Photographed iiatunil 



siiie and magnified four diameters. 



colour values are 



rock if the 



slighth' over-corrected. Some- 

 times the same result can be even 

 better obtained by the use of a filter of red, blue, 

 or green, or some other intermediate tint, or In- 

 making part of the exposure with one filter and 

 part with another. I have tried this with success, 

 but have generallv foundthat.it requires too much 

 consideration in planning and too much care in 

 carrying out to be of much practical use in the field. 



Colour Photography. 



But to obtain the very best results it is necessary 

 to photogra[)h plants in their natural colours. 

 Nothing can exceed the beauty and charm of a 

 flowering plant growing in its natural home and 



