The Optical Lantern and Cinematograph Journal (Nov 1904-Oct 1905)

162 THE OPTICAL LANTERN AND CINEMATOGRAPH JOURNAL. ^ Stereoscopic Notes. <f Hint to Stereoscopists. The halftone illustration on this page is intended to show the evils arising from too great a separation of the lenses or view points in stereoscopic photography. It should always be remembered that there is a normal angle in binocular vision, which must be regarded if complete success is to accompany one's work. The normal separation of the human eyes, measuring the distance between the pupillary centres, is found to be 2j inches For all general landscape work in which the nearest object is not closer to the camera than 6 feet, a separation for the lenses of 2=f inches will not be too much to give an accurate stereoscopic perspective ; if, however, the lenses are displaced a distance apart of 3 to 4 inches, an exaggerated relief will be the result, and the twin photographs so obtained will give the observer some considerable difficulty in his endeavours to coalesce the pictures. An instance of this sort will be clearly demonstrated if the reader will examine the accompanying reproduction in a stereoscope. It will be noticed that the boy's left arm appears twice the length from the hand to the elbow as it is measuring from the elbow to the top of the shoulder. This steieoscopic falsehood has its analogy in single picture making when a wide-angle lens is used A lens that exaggerates the size of a near object and throws it all out of proportion with other objects at a more remote plane. A Transposing Stereoscopic Camera. It is well known that when stereoscopic pictures are obtained by means of the ordinary twin-lens camera, the double positive from the negative so obtained requires cutting apart for the purpose of transposition. The two pictures have to change places before they are in their proper order for examination in the stereoscope. This troublesome stage of the work often leads the amateur to make mistakes, especially when the prints are mounted separately. Many workers prefer to cut the negative asunder and remount on a supplementary glass after changing the position of the dissimilar pair This precaution makes after mistakes impossible, as the prints will then be on one sheet of paper and always in their proper order for the stereoscope. To those who find this work of transposition of the prints or negatives a tedious operation, the transposing camera at J. S. A. Tournier, Bourges, France, may prove a welcomed novelty. As will be seen by reference to the accompanying cut, transposition of the dissimilar images is produced by means of reflecting mirrors or prisms. The rays entering the lenses at a are reflected from b to i1 and from thence to the film c. Thus the image taken by the left lens is received on the right hand portion of the film, whilst that taken by the right lens is received on on the left hand portion of the film. The consequence is that when the print is taken from the developed film, and the print is inverted the pair will be iu their proper order for immediate examination in stereoscope In connection with the subject in hand it may be mentioned that the instrument which we described on page 101 of this Journal called the Stereo-Photo-Duplicon also makes provision for direct transposition of the twin images received upon the sensitive plate