With the image sensor plate removed, three tiny springs will be seen in the lens back plate. These are very easily lost. Remove them with fine tweezers and put them somewhere safe.

A very thin coated glass infrared filter will fall out if the lens is inverted. On no account touch it with your fingers. It may be cleaned if necessary, however this is unlikely as the rear face is sealed from dust except during disassembly and the front face is normally protected by the focussing lens in its rest position.

The infrared filter may be replaced by a red filter if your aim is to convert the camera for near-infrared use.

The image sensor itself should not need cleaning unless contaminated while disassembled. Should it be necessary, first peel off the rubber surround. On reassembly, do not attempt to reattach this to the image sensor plate but rather place it over and around the glass window.

On reassembly it is important for accurate focussing that the 3 screws are each tightened by the same number of turns and to the same positions as before disassembly. Apply screw locking compound to the heads to prevent movement.