• Focal length: 5mm
  • Outer diameter: 12.7mm
  • Material: PMMA

The illumination needs a condenser lens, and so far I have generally sourced these in bulk from China. They are designed for collimating LEDs, and don’t produce a beautiful image, but they are adequate for our purposes. Searching AliExpress for pmma lens 5mm and looking for a diameter of 13mm usually brings up the right thing. Previous links aren’t very useful as they don’t stay alive for very long.