Hi @j.stirling, we did the same for our microscopy stage. As I mentioned before, we wanted to improve the FOV and working distance, so we tried with other cheap lenses. However, the lens from the PiCam is much better, as @WilliamW pointed out. It is worth to keep it in the final design.
So, I would go for a 2-lens system including the original lens and Pi cam v2. I remembered this design from Fernan.
On the other hand, moving to the Pi cam HQ seems a trend for this kind of application such as the Enderscope or this new design called “Entomoscope”:
In terms of reproducibility, any optical component is always an issue in South America. Unfortunately, an extra lens, a lens that doesn’t come with the hardware, is not cost-effective for prototyping. Shipping costs can be more than the product. I’m not sure if it’s the same in Panama. That is why a USB microscope is so attractive as a solution for some applications (?)