Objective prisms are a great way to get started in spectroscopy before maybe upgrading to a more advanced, higher resolution, ALPY or Lhires system.  The problem is getting hold of a prism, but this is one niche area where making your own is still a reasonable option.

In case anyone is interested, this is how I do it.

Optical Glass: H V Skan in Solihull, UK are distributors for Schott optical glass.  They have an online stock list of pieces that can be useful for prism making in the range 15 to 20cm. The price is just £25/Kg whatever the glass type.

Image A shows a block of Schott KF6 crown glass that was the starting point for making a 20cm, 9 degree prism.  Initial weight 5Kg.

Image B The first task is to cut out a disc using a large ‘biscuit’ cutter and 80 grade carborundum.

Image C After 8 hours cutting(!) to get through 50mm of glass the disc is ready for the next stage.

Image D Grinding a wedge isn’t covered in the telescope making books but I found the best way to do it reliably was to add some glass at the start.  Plate glass pieces are stuck to the optical glass with Araldite forming a step structure.  When this is flipped over and ground flat the desired wedge angle is ground into the substrate when all the plate glass has ground away.  Half the prism angle was ground on each side. Total time for this stage was about 30 hours.

See Part 2 for the rest of the process.