Step by step

Step 1

After carefully drilling holes (approximately 18mm diameter) in the base and lid, paint the inside of the tube with matt black spray. We shook some sawdust around inside when the paint was wet and then repainted it to make it really non-reflective.

Step 2

Taking care, form the slit by taping two fresh razor blades across the hole in the base. We taped up one side of each blade first to minimise the risk of injury while we experimented with the gap where wider equals brighter, narrower equals finer definition.

Step 3

Cut a small section from the CDR and then peel off the foil label by applying, then removing, sticky tape. Cut a holder (with a 12mm hole) from some card. This will be taped to the underside of the phone platform, so the grating covers the smartphone camera lens.

Step 4

Stick a plywood disc, with a central hole, to the lid. Use a small hinge to join it to the phone platform. Cut a curved slot in the side section and glue an M4 screw (with washer and wingnut) into the edge of the phone platform so you can set the angle.

Step 5

After positioning the phone on the platform so the camera lines up with the grating, make some ‘walls’ from strips of wood. We made a small notch in the side of a long wall so we could hold the phone in place with an elastic band.

Step 6

Before the final paint job, test the spectrograph to make sure the platform angle is set right and the slit and grating are aligned. When you are happy, glue up and use craft foam and tape to mask any gaps and prevent stray sources of light.