CHRONOMETRIC SHUTTER (Pr., Obtura teur chronometrique ; Ger., Chronometrischer Verschluss) A shutter mechanically geared to give a pre cisely timed exposure, or successive exposures at accurately recurring intervals.
The art of making photographic records of the motion of an object in chronological order.
In the year 187o, Prof. E. J. Marey, of France, commenced his researches on the analysis of motion, and the advance in sensibility of photo-surfaces has lent continual aid from that time onward. The object of chrono-photo graphy is to discover the successive attitudes which collectively make up a given motion, and to embrace phases of 0. swiftly-moving object otherwise escaping the notice of the unaided human eye. From a physiological point of view, this branch of the photographic art has proved of inestimable value, and it has served to dispel from the minds of artists certain erroneous ideas hitherto held regarding the various poses assumed by animals, birds, and the like, during the evolution of their movements.
In the year 1865, Messrs. Onimus and Martin exposed the bared heart of a living animal before an open lens for the purpose of photographing it while in motion. With the low degree of sensibility then obtaining among photo-surfaces, the exposure necessarily extended over one or more pulsations of the heart, but as a pause takes place at each extreme of the heart's beat the outline of these positions was better defined than the space between, and a record was there fore obtained of the maximum and minimum limits of a pulsation. Clearly it is only necessary to secure outlines of several intermediate posi tions in order that the experiment should attain this character of chrono-photography, properly so-called. A photograph of a man lifting his arm would (if the exposure lasted during the whole movement) result in a blur, but if a number of separate exposures was made in the same time a series of overlapping images, equal in number to the exposures, would occupy the place of one exposure blur, and the outlines of these images would in addition form a perfect record of the successive positions of the arm. An ocular demonstration of these phenomena may be readily produced by means of any ordinary photo graphic camera, supplemented with a disc per forated with a number of holes, and so attached to the lens that by rotating the disc each of the apertures comes opposite the lens in succession. By pointing the apparatus to cover a man walking along the footpath, and observing the inverted image on the ground-glass screen of the camera, meanwhile rotating the aperture disc, successive and clearly defined images of the man will be seen. Marey's chrono-photographs were obtained somewhat in this way, and diagram A shows his of a seagull. One of them is remarkable for showing the wings in a downward position. It is a curious fact that European artists seldom or never represent this downward stroke of the wing, but that the Japanese frequently do. Two years after Marey started his researches in precise apparatus. A sensitive plate was placed in a slide at P. A disc with apertures revolved between the lens and the plate. On turning the handle at the side, which communicated the necessary motion to the disc, a rapid succession of images was secured. Marey found that the images, which were almost superposed, made it difficult to distinguish individual phases. To
overcome this defect the subject, as shown at B, was attired in a black velvet suit, with dots and white lines marked thereon. During the act of photographing, the subject ran, jumped, or walked against a black background, in a direction at right angles to the axis of the lens. The result was a (negative) image, as represented at C, in which each separate attitude of the head, left arm, and leg can be easily distinguished. Such pictures provide valuable data in physio logical research. In order to secure complete and detached pictures of birds in flight, Marey contrived a photographic gun (see " Gun and France, Muybridge, of California, began to vestigate the progressive movements of animals, his operations being carried out in the open air, as shown at F. In i877 he erected a long shed containing a battery of cameras, and stretched in front of it, at right angles, a series of threads, which became broken as the subject (a man on Revolver Cameras "), which was of real value for analysing motion in such a way that the record could be subsequently re-compounded by means of the zoetrope (which see). D and E are enlargements from two of a series of pictures obtained with this gun, representing the flight horseback) proceeded along the course. The breaking of each thread communicated elec trically with the corresponding camera in the shed, and effected the necessary exposure just at that moment when the horseman was oppo site the lens. A slanting fence-reflector formed a suitable background for the subject, which was silhouetted against it, and the ground was covered with indiarubber to prevent dusty clouds flying from the horse's hoofs. Muybridge's chrono-photographs of animals in motion, espe cially of the horse, gave rise to much contro versy. The first thought on looking at some of the attitudes portrayed is that they are unnatural and impossible ; but the matter is explained when it is remembered that the eye has a certain peculiarity not shared by optical instruments, namely, persistence of vision. An impression of everything looked at remains upon the retina for about one-eighth part of a second ; and it is obvious that movements occurring in less time than the period named cannot be appreciated by the eye. In looking at a galloping horse the general effect of the movements is observed, and they are involun tarily commuted into three or positions. Such positions have been adopted by artists from time immemorial, and we have thus come to regard them as being correct.
The Muybridge system of chrono-photography was modified by Anschiitz, of Lissa, in Prussia, who added many new features to the apparatus and secured results superior to those of the earlier investigator. Prof. Marey, already alluded to, later devised a camera in which a roll of sensitised paper could be used, and finally substituted transparent celluloid film. His final apparatus is shown at G. A clamp H is sup ported by a spring frame j. A cam ic effects the feed motion of the film P, which is wound upon rollers or spools 1, and M. By means of this instrument Marcy was able to secure a much longer series of pictures than was possible with his earlier machines. (See also under the head ing " Kinematography.")