The Optical Magic Lantern Journal (October 1902)

AND PHOTOGRAPHIC ENLARGER. 5 The effect of varying intensity of light on the merit of Slides. By Rey. T. Perkins. slides, and award prizes in competitions, without throwing the pictures on the screen ; with this opinion I fully concur, although there i is often said that it is unfair to judge lantern are cases inWhich, without passing them through the lantern, many slides might be weeded out, so as to shorten the time occupied in judging; for instance seascapes in which the horizon is not horizontal, architectural views in which the vertical lines are not parallel to one another (provided of course that the want of parallelism is not due to subsidence of the foundations which has thrown the walls or pillars out of the vertical) would not be in the running, and therefore might fairly be rejected at once, so might those which are marked by glaring technical defects, such as stains or lines due to the developer having been arrested when first flowing across the plate. But even when the slides are passed through the lantern it by no means follows that a satisfactory verdict is arrived at. First then is the ‘ personal equation” to be dealt with; the partiality that the judge has for sone special colour must be taken into account, many holding that the colour of the slide should be adapted to the subject, others saying that, as in monochrome it is impossible to represent the colours of nature, the colovr of the slide is a matter of no importance, and that as one artist may sketch a head in red chalk while another uses black, and no one would think of preferring one of these pictures to the other on account of the colour of the crayon employed, so a slide should be judged by its composition and its artistic and technical excellence, regardless of its colour whether it be black, brown, purple or red. By having several judges, cach marking simultaneously but independently as each slide is projected on the screcn the personal proclivities of the individual judges are minimised, but even when this has becn done a most important factor remains and that is the intensity of the light upon the screen. This depends on the intrinsic brilliancy of the illuminant and on the extent to which the image is magnified. It may easily happen when projecting three slides A, B, C all from the same negative, each rather denser than the preceding one, that with an oil lamp, A may be the best, C being pronounced altogether too heavy, while with a mixed jet B may take the first place, and with a blow through jet C may be the best, A appearing thin and washy and B somewhat weak. In this case we are supposing that the projected images are all of the same size: If however the oil lit lantern is brought closer to the screen the size of the image will be decreased and its brilliancy increased, and as the size is gradually decreased first B and then © will look best on the screen. It would be well if a certain standard ratio of intrinsic brilliancy to the size of the projected image could be fixed, so that makers of lantern slides could insure the result at which they aimed being shown when the slide is projected ; at present all is only haphazard, and makers of slides are working very much in the dark. The slides they make may be satisfactory when projected by means of their own lanterns, and yet may be quite unsuited to exhibition when another lantern or a different magnification is employed. These thoughts have been brought forcibly before me by the result of voting and the criticism on aset of slides by members of a lantern slide exchange club of which Iam “Hon. See.” In this club each member sends in a set of four slides, the weneral subjects such as architecture, seascape, landscape or figures being set in regular rotation, the box of slides is then sent by parcel post from member to member, each is required to assign marks 0, 1, 2 or 3 to each slide and is invited to criticise. The marks assigned have in several rounds been so different, the same slide sometimes receiving 3 marks from one member and only 1 or even 0 from another, that I came to the conclusion that something more than individual taste of the votes must have conduced to this result. I therefore requested members to mark on their voting sheets particulars of illuminant used and size of the projected picture. They have not all answered this question, but sufficient have done so to show under what widely different conditions the slides were shown on the screen. One member uses a 4 wick oil lamp and projects on a screen 7-{t. square, it is almost needless to say that he marks a number of slides with 0 or 1 criticising them as being “over dense,” another uses a similar lamp and a screen 4-ft. square; on this miember’s voting sheet better marks are given to the slides marked over dense by the previous member, a third, (myself) uses with a similar lamp a sheet of cardboard 15 inches square as a screen, and marks some of the slides as weak and only a few as “rather heavy,” another uses an oxy-hydrogen jet and a 7-ft. screen and here again the heavier slides receive high marks, another who however does not give particulars, though his light is evidently very strong, marks as “rather weak” slides that the last mentioned member criticised as excellent, while he condemns as wishy-washy a good many of those which received the highest