Arizona silver belt., 1899-11-30
TELEPHOTOGRAPHY.
How Long Distance Photography Is to
 Be Made Use of in the TransVaat

How Long Distance Photography Is to
 Be Made Use of in the Transvaal.
 The telephoto equipment which IS being sent by the British Government to the Transvaal to be employed in in- dicating the exact position and forma- tion of the enemy, represents valua- ble advance in photography, says the Globe Democrat. It is intended to give in accurate detail what has here tofore been done in a more or less rough and uncertain way by recon noitering parties. The prints are ready within seven minutes of the focusing of the picture. A balloon can be sent up to height which com mands vast area of country, and from the car of the balloon compre- hensive picture can be taken, which can quickly be developed and passed down a line to attendants in waiting below. ! The advantage of the telephoto lens is that it enables any particular part of landscape to be enlarged and shown in greater detail than the rest of the picture. For instance fortiti- cation. say four miles away, which would be almost, invisible in an ordi- nary photograph, can be brought out so distinctly as to afford all the infor- | nation which the photographing ob- server is seeking. To produce a photo graphic plate an image that fairly resembles what our eyes see, requires lens of much longer focus than is generally used, and the camera that would permit the use of such lens would be unwieldy and far too cum [ bersome for ordinary photographic work The telephoto lens overcomes this difficulty by producing the effect of d lens of long focus in very com pact camera. While the method of using the telephoto attachment is very simple, it requires extreme care, | especially in the matter Of focusing. After an exposure has been made in | the ordinary way upon certain object, | the lens is removed from the camera ! front and screwed into the tube of the | telephoto attachment, forming small | telescope. The whole combination is
 then put back on the camera as if it ! were the ordinary lens. There is then seen on the ground glass, or focusing screen, an enlarged image, which may
 be made sharp or distinct by adjusting | the focus by rack and pinion move ment on the telephoto tube, just as a i field glass is adjusted to suit the eye of | the observer. If it is desired to make
 the picture still larger the front of | the camera is moved, carrying the i lenses further from the ground glass,
 and the focus is readiuSted. as before.
 In fact, the attachment forms a lens of
 variable focus, changeable at the pleas
 ure of the operator within the limits of the camera. With an attachment s inches from the plate, the image is equal to that formed by an ordinary
 lens of 24 inches focus: while at 24
 inches from the plate it is equivalent
 to that of a lens of 64 inches focus.
 The telephOtO lens has already done good serylce in military operations, particularly in Africa, and it is ex- pected that its use in the Transyaal
 will afford information which will be
 invaluable in verifying routes and
 preventing columns losing their way,
 as well as rendering them practically
 independent of guides when advancing on unknown ground.