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I've been mulling what it would take to make a lens from scratch, particularly a projector lens. With proper machining equipment, I believe I could construct every part of the lens except the actual glass elements themselves. As far as designing the optics, instead of ordering custom glass elements, I could take advantage of the low cost of mass produced elements from companies like Edmund Optics. However, I'm wondering just what kind of tolerances in the glass thickness would be acceptable. For example, in an old episode of "How It's Made", they show the construction of a Canon EF 500mm F4 L IS USM lens, a $9000 lens, and they mention that the glass elements have a tolerance of +/- 0.001mm. That kind of a lens has far more precision than I would need. The cheapest elements from Edmund Optics however have a tolerance of +/- 0.1mm., something I would guess is way too low, but I'm not sure. This is for projecting Super16 film in a modified projector. Really, I don't think I would need better precision than what you would find in a $100 DSLR kit lens. My question is: What kinds of tolerances would be acceptable, and/or what kind of precision is used in mass produced kit lenses.