Movie Makers (Jan-Dec 1948)

152 Choosing your projector Lamp power? Lens speed? Footage? Here is all you'll want to know about these features O N the preceding two pages. Movie Makers presents a fact and figure survey of 8mm. projectors currently being offered to the amateur filmer. Discontinued models are not covered. There are thirteen of these instruments, produced by nine different manufacturers. Twelve of them are silent. One of them has sound on disc electrically synchronized with films especially prepared for such presentation. So that the new filmer may evaluate the differing capacities of these instruments informedly, we offer herewith a general discussion of the chief features to be found in these 8mm. projectors. FUNCTION OF THE PROJECTOR Obviously, the primary function of any projector — be it still or cine, 8mm. or 16mm. — is to project onto a screen an image of a size, brilliance and sharpness adequate to the audience which the instrument is designed to serve. With the 8mm. projector (as we saw last month in the discussion, Eight or Sixteen?), this audience is primarily a home one and always a relatively small one. It is not to be expected, therefore, that an 8mm. projector can create images of large screen size (say, six feet in width or larger) comparable in brilliance and sharpness to the images created by a 16mm. projector of equal capacities. Within its own designed limitations, however, an 8mm. projector can and does create images of highly satisfactory quality. This basic viewpoint should be kept in mind by the new filmer as he assesses the capacities of the thirteen projectors surveyed. Let us now see what, specifically, these capacities are, as well as how, in general, they contribute to the end product — the screen image. LENS SPEED Broadly speaking, the adequacy of image size, brilliance and sharpness is controlled (as far as the projector is involved) by lens speed and lamp power. The design efficiency of a projector's optical system also plays an important part — but it is impossible to evaluate this factor comparatively either in the survey or in this discussion. It is possible, however, to review the known technical facts of lens speed and lamp power. Of the thirteen projectors surveyed, then, we find that ten of them offer lenses with a speed of //1.6, one of them of //1.85 and two of them of f/2. These designations of projector lens speeds mean, in efficiency of image illumination, exactly what they do when used to designate camera lens speeds — the relative ability of a given lens to pass onward the light reaching it. The smaller the // number, the greater the percentage of the total light that is being projected to the screen. All of the lens speeds noted above are regarded as "fast," or as passing a relatively high percentage of the total illumination. The difference in speed between the fastest (//1.6) and the slowest (f/2) is approximately JAMES W. MOORE, ACL three quarters of a stop. This will mean that the f/1.6 lens — all other factors being equal, and there are a number of them — will pass about one and one half times as much light as the f/2. To sum up, then, roughly 77 percent of the projectors surveyed offer the f/1.6 lens, 8 percent the //1.85 and 15 percent the f/2. LAMP POWER In the matter of desirable lamp power, there is not — among the thirteen projectors — such a consensus of selection as was found with lens speeds. Seven of the thirteen provide for the 750 watt projection bulb; five offer the 500 watt and one a potential capacity of 1000 watts. (The Dejur 1000 comes equipped with a 750 watt bulb, but can accept the 1000.) The selection of a projector using one or another of these bulbs will depend, almost entirely, on the maximum screen size you desire for your projected pictures. Certain it is that the 500 watt lamp, teamed with any one of the lenses noted, will provide (on a good screen) an image 30 by 40 inches in size, of very pleasing brilliance. Able and experienced amateurs — again in the discussion, Eight or Sixeten? — have reported using the same combination satisfactorily up to 48 inches in width of screen image. Using the higher wattage lamps coupled with the f/1.6 lens, 8mm. projection can be carried easily to the 48 inch limit and, if necessary, to a 60 inch width. It should be kept clearly in mind, however, that large screen size is not in itself a desideratum. There are practical, and even ocular, considerations. For example (on the practical side), even the 30 by 40 inch screen image will require that your projector be 18 feet from the screen; the 48 inch width calls for a 22 foot throw, while the 60 inch screen pushes your projector back to 27 feet. You will want to think twice before involving yourself in such a projection setup in the average home! In the field of audience eye comfort, the new filmer should realize also that it is quite possible to project both too bright and too large a screen image. The brightness level can be checked visually simply by whether or not it produces eye strain; another guide to over-illumination will be found in washed out color images projected from basically well exposed films. The size of your screen image in relation to audience placement has a definite and generally accepted rule. No spectator should be forced to sit closer to your screen than a distance three times the screen's width. If your home cannot provide these seating arrangements, you need a smaller screen. Finally, in the matter of lamp power, do not attempt to install in your projector a bulb of higher wattage than that specified by the manufacturer. This is neither a safe nor an efficient practice. For these bulbs, in producing their spectacular amounts of light, also produce an amazing amount of heat. The cooling system of any given projector is specifically designed to carry off safely the heat of the recommended [Continued on page 163]