Small magnifying glass out of an old webcam (you can also find these inside laser pointers, disposable cameras or old DVD drives).
Mark and cut out three 20cm x 20cm squares of cardboard. In each square make three holes that the screws can fit through – two in a corner and one halfway along the opposite edge. These will be the three levels of a microscope.
The base level is ready. For the middle level, cut a rectangular hole the size and shape of one side of the CD case out of the cardboard. Fix one side of the CD case into it with the Blu tack.
For the top level, cut out a window big enough for your smartphone’s camera to see through, making sure it lines up over the CD case when stacked on top!
Thread three upturned screws through the holes of the base level and secure a wing nut about a third of the way down each screw.
Slot the middle level onto the screws so that it rests on the wing nuts. Then secure a screw nut onto each screw, leaving a 1cm gap above the middle level. Finally, slot in the top level.
Take the magnifying glass, place it flat side against your smartphone’s camera hole and fix it in position with adhesive tack.
Complete the microscope with a piece of white paper on the bottom layer and the phone on the top, with the lens pointing through the window. Prepare the object you’d like to magnify on the spare CD case and slide it into the middle level under the lens.
You may need to adjust the focus of your camera lens by moving the middle layer up and down. Do this simply by twisting the wing nut directly below the camera.
Once everything is in focus, take a photo of your object. Some interesting things to get kids involved are the thing outer layer of a red onion, a blade of grass, sugar crystals or the tiny illustrations on bank notes!