This treatise is addressed to those who practise photography either for pictorial or scientific ends.

The late Michael Faraday once remarked : "Lectures which really teach will never be popular; lectures which are popular will never teach." All writers must experience the same inherent difficulty of treating scientific matter in any but an academic style. The author has endeavoured to present the subject of Telephotography in a manner which presupposes only the very slightest acquaintance with the science of Optics, explaining fully only those few properties or functions of lenses, which are necessary to enable the photographer to understand the action of the Telephotographic lens, and to comprehend the wide possibilities of its applications.

The aim of the present work, in short, has been to call attention to the scale in which objects are reproduced in the image by ordinary photographic lenses, and to show how this image may be subjected to direct enlargement or magnification before it is received on the photographic plate.

Photograph of Mont Blanc

Frontispiece

Photograph of Mont Blanc, reduced from a negative 20 x 16, taken by Fred. Boissonnas, of Geneva. The distance from Geneva to Mont Blanc in a straight line is about 70 kilometres - say, 44 miles. The smaller photograph is a reduction in the same scale from a negative taken with an ordinary 15-in. lens. (This photograph was awarded the medal 0/ the Royal Photographic Society in 1892.)

This method was adopted by the author in his original contributions to the subject. It is perhaps less classical than treating the instrument as a complete optical system, but has a more practical bearing upon its use; and as might be expected, is more readily grasped by those who are acquainted with the action of ordinary photographic lenses: both methods are, however, included. It is hoped that frequent diagrammatic representation and occasional repetition may be of assistance to the reader. The application of the few formulae given in the work only involve a knowledge of arithmetic.*

The literal meaning of the term "Telephotography" does not convey the full significance of the applications of the Telephotographic lens. The value of the instrument is as great, if not greater, in photographing near as well as distant objects. It will be found to possess invaluable properties wherever lenses of great focal length are required to produce large images on the one hand, and for rendering improved perspective drawing in any given scale of near objects on the other. This latter effect is brought about by the fact that a greater distance intervenes between a Telephotographic lens and a comparatively near object (as in portraiture) than that required when using a lens of ordinary construction of the same focal length. This property is of great value to the artist when the object he desires to photograph has any "depth of field" enabling him to avoid the apparent exaggerated perspective so frequently met with in ordinary photographs.

The principle upon which the Telephotographic lens is constructed has been applied to the astronomical telescope for nearly seventy years. So long ago as 1834, Peter Barlow, in a communication to the Royal Society, dwelt on the advantages that might accrue from employing his negative lens "in day telescopes" as well as in astronomical telescopes; "for by giving an adjustment to the lengthening lens, the power may be changed in any proportion, without even removing the eye or losing sight of the object. I have no doubt these and other applications of the lengthening lens will be made." In these last few words Barlow foreshadowed the construction of the Telephotographic lens.

* The notes to Chapters II., III., IV., V., and VI. may be omitted on first reading.

Dr. Von Rohr, a contemporary of the present writer, has been at great pains to trace the application of Barlow's lens in the construction of photographic instruments; and it appears that in 1851 Porro, an Italian engineer, utilised a "Barlow" lens for photographing an eclipse of the sun which took place on July 18 in that year. Since that date, the employment of a negative lens in astro-physical work has been adopted in a few isolated instances, notably by Dr. H. Schroeder, and these instruments are reported to have been directed to very distant terrestrial objects for the purpose of photographing them. Ordinary astronomical and terrestrial telescopes of various kinds have been utilised for the same purpose from time to time, and in the year 1873 the late Mr. J. Traill Taylor, Editor of the British Journal of Photography, called attention to the use of the Galilean Telescope, or ordinary opera-glass, for the purpose of producing a large direct image. This application of the Galilean telescope is identical with the employment of the "Barlow" lens for direct enlargement of the image, and as the instrument was not designed or corrected for photographic purposes, the reference to the opera-glass, although occurring in photographic literature, was unnoticed elsewhere.

In February 1890, Steinheil constructed a special photographic instrument upon this principle for the German "Reichs-marineamt," but the fact was not published.

In the autumn of 1891, A. Duboscq, Dr. A. Meithe and the author almost simultaneously applied for patents concerning Telephotographic instruments; Duboscq in France on August 7, Dr. Miethe in Germany on October 18, and the author in England on October 2. Duboscq's work was not known till a reference was made to it by A. Sorets in 1893.

A controversy between the author and Dr. Miethe as to priority took place in the British Journal of Photography, in which the author acknowledged Miethe's independence. At this date there had been no previous publication of instruments designed for the use of photographers.

The author was the first to exhibit instruments so designed at the Camera Club, London, and to explain the theory of construction and working. This is acknowledged by Dr. Von Rohr (of the firm of Zeiss), who points out the widespread effect of this exposition.

The inherent defect of distortion of the image in the first Tele-photographic constructions led the author to introduce the plan of converting ordinary non-distorting photographic lenses into Telephoto-graphic systems, without interfering with their ordinary use, and this form of combination is the one which is now chiefly adopted by his contemporaries. Full reference is made to particular constructions.

The author desires to record the fact that his attention was first directed to the subject of Telephotography by his friend Dr. P. H. Emerson, who urged upon him the necessity of a photographic instrument to enable the naturalist to record incidents that were then only possible by telescopic observation. Emerson's original work in advancing the pictorial side of photography is now history, and it was his indication of certain drawbacks in photographic methods, as a means of pictorial representation, particularly the inadequate rendering of objects as seen by the normal eye, that led the author to endeavour to overcome them by improved optical means.

M. Boissonnas, of Geneva, the Earl of Crawford, and Mr. Hodinott, of the Camera Club, London, were the first to test and prove the value of the instrument in distant mountain scenery, and Dr. Emerson (in 1892) and later Mr. J. S. Bergheim to exhibit results showing improved perspective in portraiture. The author's thanks are due to these gentlemen and many others for their kindness in offering examples to illustrate this little work. Mr. R. B. Lodge and Messrs. Kearton have exemplified its value to the naturalist, Mr. E. Marriage and Mr. Cruickshank to the architect, while Dr. Victor Corbould and the late Dr. Fallows have demonstrated its utility in surgical and medical records; some of their splendid work would have been here reproduced, except for reasons that will be obvious when it is remembered that this treatise is intended for perusal by the lay public. A few studies of the eye are therefore substituted. The Astronomer-Royal kindly lends two very interesting examples of solar photography, while Naval and Military records and possibilities are illustrated through the courtesy of representatives of the Japanese and Italian Governments.

It may be mentioned that with the exception of one or two articles on the practical applications of the lens by Mr. Lodge, Mr. Marriage and Dr. Spitta, the subject has not been treated by any other English writer.

The author's papers are scattered - some being out of print. He therefore hopes that this treatise may find acceptance, and a place in the literature of photographic optics.

Royal Societies Club,

St. James's Street, W. September 1899.