What you’ll need
▶ A bright, adjustable-focus compact LED torch with a removable lens.
▶ A plastic tube with a length equal to the focal length of the lens plus about 30mm. The tube needs an inside diameter slightly greater than the outside diameter of the torch.
▶ A converging lens with a focal length of 100mm to fit inside the tube.
▶ Mouldable glue to make the lens cell and to cement the tube to the torch.
▶ A saw to cut the tube, a file to deburr the cut end, an abrasive pad to finish smoothing the cut end, and a dowel to shape the inside circumference of the lens cell.