MAKING SINGLE FLAP SHUTTER.
The single flap shutter (Fig. 931) is a very simple type, consisting of a flap, A, which is raised by a rubber band, and is closed by means of a weighted arm, 13, attached to it. For convenience of de scription, it is assumed that the shutter is to be made for a lens whose greatest working aperture is 1 in. The dimensions can be calculated easily for a smaller aperture. The back of the shutter is a rectangular piece of wood about s in. thick, and not less than 1 in. broad, the breadth being about a in. more than the diameter of the hood, or mount, of the lens the shutter is to fit ; the length will have to be determined later. On the back of this wood, and equidistant from three of its edges, mark out a circle having a diameter equal to that of the lens mount ; bore a small hole through the centre of the circle, and with this hole as centre, on the other side of the wood mark a square of 14 in. side. Cut away the
wood enclosed by this square to a uni form depth of about in., and then bore a hole of suitable diameter by means of a centre-bit right through the wood, its centre being the small hole already bored. Reference to Figs. 932 and 933 will make this clear.
full lines shown in Fig. 9:35, and bend back the pieces a a behind b, and hammer flat. Now bend b at right angles to c, and solder to Front of flap as shown in Fig. 931. It is well to run a little solder be hind b to prevent it being bent back ; also file off any sharp corners. The flap is now complete, and two grooves should be cut across the wooden hack, so that when the flap is placed in the recess the wire does not prevent it from fitting closely over the hole. It is well to glue a piece of thin cloth round the lower part