The Art of projection and complete magic lantern ... - Yesterday Image

lOOhalls. Some school rooms have roofs with a very low pitch, the acuteangle of the roof preventing the use of a large sheet. The screen shouldalways hang at a sufificient height to clear the heads of the audience.Whenthe lantern is tilted at an angle, the screen should also be placed at anequal angle, or the picture will appear egg shape, being out of focus topand bottom. When tilting the screen in this manner, care must be takento pull it very tight else it will sag, with a convex surface like a sail. Greatcare must be taken in the seams, that the join is not strained or puckered,as nothing looks so bad as to see every portion flat and even with theexceptionof the seams. The widest material for screens without a join is 9 feet,above that size a screen must be joined. When the join is at the bottomit is not seen, appearing as it does in the foreground of the picture. Whenrequiring to show through the medium, it should be wetted by the aid ofa garden syringe. Never do this unless it is absolutely necessary, as ittakes all the whiteness out of the material, which is not recovered againin ordinary washing. Where possible, a screen should be retained, speciallyfor this purpose. If in time the dirt makes itself visible, send the sheetto a laundry in the provinces, and have it bleached, the smoke and smutsof our big towns do not admit of this being done properly.Always show on where possible. It may appear superfluous to add,that it is not necessary to wet the screen for this purpose.Opaque.—Opaque screens are a luxury, but very effective andclean. When a lantern is frequently used in one place, as an instituteor school, the screen can be made a fixture, and rolled up out of the way,it has the advantage of being clean and ready for use. There is aslight gain in light over an ordinary sheet, but nothing like the amountoften estimated. For travelling about they are out of the question theroller and keeper top and bottom making them very unwieldy. Theyare made exactly in the same manner as maps, the canvas beingcoveredwith paper, when this becomes dirty it must be re-papered. It wouldnot do to whitewash ft, as it would flake off, when rolled up. With thelarger sizes there is a great falling off" of flatness at the sides, this canalways be remedied with an ordinary, but not with an opaque screen.The best form of opaque screen is a white washed wall, nothing isbetter. If it is rough, it may be papered, and a coat of wash will alwaysbring it u[), do not put any blue in the wash, a little black is preferable.For microscopic work and where a small picture is required, tracingpaper stretched on a frame forms an excellent medium, and it may nowbe obtained 60 inches wide.