Step by step

Step 1

You can establish the required length of the tube by setting the torch to half its focal range, 5m or more from a blank wall, and holding the lens in front of it to give a sharp image of the LED on the wall (shown inset).

Step 3

Use a sharp saw to cut the pipe. An ordinary handsaw will suffice for plastic pipe but, if you are using metal pipe, you will need a hacksaw with a blade of 24 teeth per inch or finer. Use a file to deburr the cut edge.

Step 5

Clean the lens and put it into place, then make a thin sausage of mouldable glue. Carefully feed this around the inside of the tube, in contact with the lens, then smooth it into place so that the glue firmly adheres to the tube.

Step 2

Mark the tube at the required length. Wrap a sheet of paper around the tube at the cutting mark, then mark around the edge of the paper to give a cutting line that is at right angles to the length of the tube.

Step 4

Make the inner part of the lens cell with some mouldable glue. You can use the lens itself to push it to the correct position in the pipe and shape the front of the cell with a wet dowel to obtain a smooth inside circumference.

Step 6

Set the torch to mid-focus again and slip the tube over it. Note the position for best focus, then use mouldable glue to cement the tube into place. Leave it overnight for the glue to set, then smooth any rough edges with the abrasive pad.