. The book of photography; practical, theoretical and applied. Fig. 49.—Determining Position opLens Stop. stituted. Draw a square each side ofwhich is equal to the focus of the lens, asp(Fig. 49), and a diagonal line H K, andfrom its centre erect a perpendicular J Mequal to the focus ; at M draw a line N oequal to the diameter of the lens. Nowdraw two lines from H and K through nand 0 until they meet at L. The distancefrom M to L is the distance required. Making stops may be cut from sheet brasswith a fret-saw to fit the diaphragm open-ing, afterwards blackening with deadblack solut
. The book of photography; practical, theoretical and applied. Fig. 49.—Determining Position opLens Stop. stituted. Draw a square each side ofwhich is equal to the focus of the lens, asp(Fig. 49), and a diagonal line H K, andfrom its centre erect a perpendicular J Mequal to the focus ; at M draw a line N oequal to the diameter of the lens. Nowdraw two lines from H and K through nand 0 until they meet at L. The distancefrom M to L is the distance required. Making stops may be cut from sheet brasswith a fret-saw to fit the diaphragm open-ing, afterwards blackening with deadblack solution, the composition of whichis given on another page ; or they may becut from sheet ebonite. Parting Cemented Lenses. Cemented lenses may be parted in thefollowing way : Lay a piece of wood in tho. Fig. 50.—TvpiCAL Studio Camera. soap and water. Be careful to rememberwhich surfaces were together. When thelenses have been finally polished up witha wash-leather, a drop of best Canada bal-sam, baked until it has become hard, andthen made hot so as to be thin enough foruse, is applied to the centre of the concavesurface and the other pressed down uponit till it spreads evenly. Warm the lensesbefore doing this. Now bind the two to-gether with string, winding round andround in all directions. Heat the lensgently until the balsam is thoroughly hard,which may be asceitained by testing thatwhich has oozed out at the edges. Re-move the string and clean the edges withether, and it will be ready for re-insertionin the cell. The Studio camera for studio work requires anextra amount of strength and rigidity, CAMERAS AND ACCESSORIES. 37 since it will require to stand a good dealof hard wear. It is therefore made of adifferent pattern from the field camera,in which, naturally, lightn
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