I was challenged to make a lens for a friend without buying any new optical elements. I have a pile of glass that I've salvaged from old camera lenses that I've modified. I wanted to make a cooke triplet but didn't have any negative elements on hand where I precisely knew their characteristics. I then realized that my eye glasses are relatively well characterized negative lenses, so I had an optometrist cut them into a disc shape and I built the lens around that. It performed very well in my simulations, but not so well in real life. But it was a fun project and my friend ended up with a unique lens for her camera.