It will be observed that the same negative lens is used in both cases ; if combined with the single cemented positive lens the curved surface faces the ground glass, but when used in conjunction with a double combination the flat surface is directed to the ground glass. The mounting of this lens has an engraved scale in millimetres which can be read off showing the interval (d of the formula) from which the equivalent focal length of the system can be calculated for any given separation. It is obtained by multiplying the focal lengths of the component lenses together and dividing by the interval which can be read off on the one hand, or set to produce a desired focal length on the other.

Fig. 64.

IV Telephotography For Distant Subjects 116

Dr. Miethe in his Telephotographic construction for all ordinary purposes in which distortion is inadmissible, employs a Collinear lens as the positive element, combining it with a triple cemented negative lens as illustrated in Fig. 64.

We will now call attention to some of the many other applications of the Telephotographic lens in distant photography.

(1) In astronomical work the method of direct enlargement by a negative lens corrected for photographic purposes has of late years superseded the former method of secondary magnification by means of a second positive lens. Plates VII. and VIII. illustrate the application of the negative lens to large telescopes, increasing their focal length in order to produce a larger direct image. In solar photography generally, the exposures are so short that good results may be obtained with an ordinary camera which is not mounted equatorially, and valuable records of important sun spots and partial or total eclipses of the sun may be readily obtained in ordinary photographic practice. The diameter of the image given of the sun or moon is approximately 1/10 of an inch for every 10 inches of focal length, and it is readily seen that almost any Telephotographic system will enable us to produce an image of sufficient size to be of interest.

In lunar photography, however, it is not possible to attain a very high degree of definition, owing to the apparent complex movement of the moon during the period of exposure which is necessary for obtaining a good negative; but, nevertheless, records of partial and total eclipses of the moon in progress are sufficiently well defined to be in themselves interesting. A few years ago the author exhibited some lunar photographs at the Camera Club, which have been referred to as warranting further efforts in this direction.

(2) The value of the instrument in photographing distant mountain scenery is already well known and much practised. The author has reproduced as the frontispiece a reduced copy of the historical photograph by M. Boissonas of Geneva, taken at a distance of 44 miles direct in a camera of 5 ft. extension on a 20 x 16 plate. In order that the same size of image could be produced by a lens of ordinary construction a camera 25 ft. in length would have had to be employed. Plates IX. and X. show more modest results with a quarter-plate camera, which can be carried by any enthusiastic mountain climber.

(3) Plates XI. and XII. exhibit the application to long-distance photography generally, and are purposely included as examples of what can be accomplished across the water, even in this climate, where atmospheric conditions are seldom favourable. This leads us to say that the application of the Telephotographic lens in distant photography, even when atmospheric conditions are unfavourable, enables us frequently to obtain results which are far more distinct than the impression given to the eye.

(4) The geologist will appreciate the results shown in the comparative work illustrated in Plates XIII. and XIV. In this case the cliff is at a distance of more than five hundred yards from the camera, and the details shown will point to the application of the Telephotographic lens to studies of geological formations which are inaccessible.

(5) The application of the lens to balloon photography is illustrated in Plate XV., XVI., and XVII. In this application it is needless to say that the positive element of the combination must have a very high intensity. The instrument designed by the author for this purpose consists of a portrait combination of large diameter and high intensity combined with a negative lens which is also of large diameter in rela-tion to its focal length. The value of this instrument to military departments is evident.

(6) Plate XVI11, illustrates the possibility of obtaining naval records in warfare, and suggests the use of the instrument for becoming fully acquainted with details of foreign naval equipments even in times of peace.

(7) The architect and student of archaeology will find a wide field in the application of the lens in recalling details of ancient and historical buildings. Portions of carving and sculpture in quite inaccessible positions may be photographed on a large scale on the one hand ; or, on the other, large buildings may be photographed from such a distance that they will be rendered without perspective effect, showing the true relative proportions, and being practically a plan in elevation. This branch of the subject has been most clearly exemplified by the work of Mr. E. Marriage, who gained the medal of the Royal Photographic Society in 1895. Fine specimens of the work on a large scale, kindly lent by Mr. Cruickshank, are illustrated in Plates XIX., XX., XXL, and XXII. In this particular branch of work special arrangements in the camera and stand are almost essential. We illustrate in Fig. 65 an arrangement for tilting the camera recommended by Mr. Marriage, and also a strut connecting the tripod and camera for the purpose of greater steadiness. Although the camera may have to be pointed upwards at a considerable angle, the camera back must always be plumb In these subjects where the duration of exposure is not of great moment, we can afford to employ almost the limit diaphragm for the combination, and in this case the pencils which form the image are so attenuated that it is possible to obtain fine definition even when the camera back has been considerably swung to obtain the true plumb.

Fig. 65.

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In Fig. 65 we illustrate a useful device for employment when photographing interiors of cathedrals, churches, etc., in order to prevent the legs of the camera from slipping during exposure. The underside of the three arms is lined with rubber, the three arms themselves being made of soft wood to support the points of the tripod legs.

(8) Plates XXIII., XXIV., and XXV. serve to illustrate a branch of photography referred to in the previous section, as also many similar conditions. The whale illustrated in Plate XXIII. can only be represented by an ordinary lens in painful fore-shortened perspective upon the plate, as, owing to the cramped conditions, it is impossible to obtain a broadside image of it from a view-point on the pier, or one which properly shows the relative proportions of the animal. To obtain these it was necessary to take the camera along the shore to a position where a broadside view could be obtained, necessitating a distance of upwards of three hundred yards from the whale itself. Plate XXIV. shows the result obtained by the same lens that was employed for the near view. The size of the image is now too insignificant to be of value in itself, or to bear enlargement from the photographic negative without loss of detail. By employing a negative lens in conjunction with the same positive element, we produce the result shown in Plate XXV. from the same standpoint.

(9) The application of the Telephotographic lens to animal and bird life has already been roughly hinted at. For some years Mr. R. B. Lodge of Enfield has devoted much patient care to this subject. His methods have been published in several photographic periodicals and he has lectured on the subject before the Royal Photographic Society, who awarded him a medal in 1895 for his work in this branch. Plate XXVI. is indicative of results that may be obtained in this field of work.

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Plate XXVI i) Little Grebe on Nest. Taken with Rapid Rectilinear lens ioj ill. focal length. Distance 20 yards.

(2) Little Grebe on Nest. Taken with Telephotographic lens from same standpoint. Exposure 2 seconds.

(3) Kittiwake on nest. Taken with Telephotographic lens. Distance 20 ft. Exposure 1/8 second.

(4) Rabbit. Taken with Telephoto lens. Distance 20 ft. Exposure 1/8 second.

(These pictures are the copyright of, and were kindly lent by, Mr. R. B. Lodge of Enfield.)