PHOTOGRAPHY 



PHOTOGRAPHY 



2599 



and the skilful operator may, by the use of the proper 

 plate and in some cases a suitable ray-filter, give 

 approximately correct values to all the colors of the 

 spectrum. For all ordinary horticultural uses, when 

 blue and yellow are not found in the same subject, the 

 commercial orthochromatic or isochromatic plates of 

 the most rapid speed are satisfactory. These give to 

 yellow its proper value, at the same time improving 

 the rendering of the green foliage and slightly increas- 

 ing the truth of representation in pink, lavender, and 

 the lighter red shades. 



It is very much better, then, for the photographer 

 who has to do with horticultural work to confine him- 

 self exclusively to these plates for all his work. If he 

 has a subject including blue flowers, the especial activ- 

 ity of the blue rays, which otherwise would render the 

 photographic impression as intense as if the object was 

 white, can be restrained by a suitable ray-filter, which 

 is applied in front of the lens. This ray-filter is either 

 a glass cell filled with a 1 per cent solution of potas- 

 sium bichromate, or a piece of plane optical glass 

 covered with a suitably stained collodion film sealed 

 with another optical glass and provided with a con- 

 venient mounting for slipping on the lens. (Such ray- 

 filters may be commercially obtained at small cost, but 

 ought to be known to be adequate for the particular 

 plate to be used.) With this ray-filter and the plate 

 before alluded to, the yellow is slightly over-valued, but 

 the blue is given its proper relation. The beauty of out- 

 door photographs is vastly increased by the use of the 

 plate and ray-filter mentioned, because a proper color- 

 value is given to the sky, and the cloud-forms are 

 preserved in all their attractiveness. If the subject is a 

 heavily loaded peach tree, for example, the accentua- 

 tion of the yellow, brought about by the use of the 

 ray-filter, will give a needed slight exaggeration of color- 

 value to the fruit, which, under treatment by an ordi- 

 nary plate, will be almost indistinguishable from the 

 mass of foliage. With the usual ray-filter the exposure 

 required is practically trebled. In this Cyclopedia, 

 advantage has been taken of orthochromatic plates 

 in photographing many of the subjects. The carna- 

 tions, Plate XXII, Vol. II, show a variety of shades 

 properly rendered by the means indicated. The grape- 

 fruit, Plate L, Vol. Ill, is an example of the use of the 

 ray-filter also to obtain the full color-value of the fruit. 



A difficulty known in photographic practice as 

 halation must also be counteracted if the fine detail of 

 subjects involving much light is to be preserved. Hala- 

 tion is caused by the reflection of brilliantly lighted 

 objects from the back of the glass plate carrying the 

 sensitive emulsion. Light possesses enormous velocity, 

 and there is an almost inconceivably rapid play back 

 and forth between the two surfaces of the glass plate, 

 which is covered only on its face by the sensitive 

 photographic emulsion. This results in a thickening 

 of all the finer lines which should be rendered in the 

 positive as white. It may be counteracted by "back- 

 ing" the plate with a composition which will absorb 

 all the rays of light that pass through the emulsion on 

 the face; but in current practice a slightly less ade- 

 quate and much more convenient prevention of hala- 

 tion is secured in the use of what are known as "double- 

 coated" plates. A "slow" emulsion, first coated on the 

 plate, is covered by a "fast" emulsion, with the effect 

 of absorbing into the under-coating, in exposure, the 

 overplus of light. These plates, incidentally, also give 

 greater latitude of exposure, and their use is recom- 

 mended, with the provision that both coatings should 

 by all means be orthochromatic. 



Even with the aid of the isochromatic plate and the 

 ray-filter, the photography of shades of red is difficult, 

 because of the lack of actinic or chemical quality in the 

 red rays of the spectrum. In practice it is found neces- 

 sary to give a very much prolonged exposure to objects 

 containing red, and then to restrain the over-exposure 

 165 



upon development by means of a suitably compounded 

 developing solution. 



Lantern-slides. 



A. lantern-slide is a positive on glass, and therefore 

 is made from a negative. It is made preferably on a 

 special plate, much slower than the regular photographic 

 dry-plate, because coated with silver chloride rather 

 than a silver bromide emulsion. The slide is usually 

 faced with a paper mask, so as to include only the 

 desired portions of the picture, and protected by a 

 coyer glass. Negatives of any size may be used if a 

 suitable arrangement is provided for reduction. This 

 can readily be arranged by an adaptation of the camera- 

 stand illustrated in Fig. 2924. A pair of light bars is 

 added, running from the top of the plate-glass frame 

 to a support at the other end of the stand, and a piece 

 of heavy muslin or light canvas thrown over this serves 

 to exclude the excess of light. A ground-glass frame is 

 added back of the plate-glass, which latter is removed 

 to give place to a turn-table arrangement, made to 

 take and hold negatives of various sizes. In practice, 

 the ground-glass end is turned toward the strong light, 

 the negative to be used is adjusted in the turn-table, 

 and the image focused in the camera as usual. The 

 5 by 7 size largely used by horticulturists is in just the 

 right proportion for the ordinary lantern-plate of 

 American practice, which is 3 J^ by 4 inches. Slides 

 may also be made by contact, if the negative to be used 

 is of suitable size. The familiar 4 by 5, 33^ by 3}^, and 

 3M by 4J4 hand-camera films are often so used, being 

 placed in contact with a lantern-plate in an ordinary 

 printing-frame, and given a short exposure to an artifi- 

 cial light. Such slides are seldom of good quality. 



If it is required to make lantern-slides from diagrams, 

 engravings or any positive material, a negative is first 

 prepared,, for making which the vertical position of the 

 camera-stand (Fig. 2925) is very convenient. For many 

 diagrams and for most "reading slides," there is much 

 advantage in making the slide directly without the 

 intervention of a negative, with the result that the 

 letters or lines are shown as clear glass. The audience 

 sees only the message or object, the background being 

 dark; and the excessive light reflection, tending to tire 

 the eyes, is avoided. 



In making lantern-slides, it is important to learn the 

 proper exposure, for errors in exposure cannot be cor- 

 rected in development to any great extent. The care- 

 ful worker will expose several plates upon the same 

 subject, give all the same development, and act upon 

 the experience thus gained. The standard all too often 

 accepted by those who use lantern-slides is unfor- 

 tunately low. Manufacturers competing wholly on the 

 lowest price basis have accustomed even thoughtful 

 persons to think their productions adequate, instead 

 of which they are unfortunate, because they belie 

 rather than reproduce the object to be shown. 



Lanterns for projecting these slides are now simple, 

 convenient, and cheap. One form, available wherever 

 access may be had to an electric-light socket, can be 

 carried in a small case and set up for use in less than 

 ten minutes. It perfectly projects an image up to 6 

 or 8 feet in diameter, and is without complications. 

 Built of aluminum, it is solid and durable, and its cost 

 is but one-fourth that of former apparatus. 



Colored lantern-slides. 



The value of a good lantern-slide is increased more 

 than tenfold if the slide is so colored as to show upon 

 the screen the object or scene in natural hues. It is not 

 difficult, with suitable knowledge and sufficient prac- 

 tice, so to tint the lantern-slide as to accomplish this 

 object, and there are a number of notably successful 

 colorists whose work has given information and pleasure 

 to thousands. 



In practice, if a lantern-slide is to be colored, it is 



