Today, out of curiosity, I took an old zoom lens apart that I had lying around. While doing this I was thinking "what if I would build a camera around one (or more) of these separate elements?". So I have a few questions about how I should approach this. First of all, how can I determine the focal length of these lenses? I'd like to build a simple box camera with a fixed focus. I'm not looking for technically perfect images so vignetting, soft images and a wide array of aberrations aren't a concern, I would just like something that is fun to build and use! I also would like to use 5x4 (if the lenses would cover it) so any tips about making the film insert lightproof would be great. I think I'd like to add a ground glass too, which I'll probably be making myself. This is the first time I'd build a camera and I don't really know what I should specifically ask, so all kinds of advice are welcome!