I'm not entirely sure in which forum I would need to post this question but Cinematography seems as likely as any other. I'm trying to build my own Mini-35 to give video a greater depth of field and more of a "film-look." So far I've procured lenses, focus screens, mounts and all the necessary accoutrement but I'm missing one thing: a biconvex lens to flip the image coming from the 35mm lens so that the image appears correctly. There are plenty of places to get the lenses but my problem arises when it comes time to choose. Is there anyone out there who knows the mathematics of lenses well enough to help me determine the size and shape I need? Also, if anyone has any pointers on construction, I'd love to hear what you have to say. Thanks!