I want to experiment with building a custom digital camera for robotics purposes, starting from an image sensor. The quality of the image need not be very high (comparable to a webcam), but the customized lens should allow me to achieve things like magnification and specific focal depth.
I came across it because at one point, there was a vogue for using these lenses with an adaptor on Micro 4/3 cameras. The idea was that you'd just dropped getting on for a thousand pounds on a camera body, so couldn't afford a lens, so you'd buy some thirty quid lens from China and use that. Needless to say, it didn't take people long to realise that was really stupid.
I think people were also attracted to adapting those lenses because there are readily available CCTV and machine-vision lenses which are, compared to typical photographic lenses, extremely fast (like f/1.0 and lower). This is for applications like security cameras which need to be able to work in dim lighting conditions, or machine vision applications that require a very short shutter speed. Of course what the Micro 4/3 crowd eventually came to realize is that in order to achieve a fast lens at a modest price point, those lenses trade off other qualities like resolution and distortion, which are less important in their intended applications, but seriously compromise the lens for photography.
Is there any source for high quality slow lenses?
Most other shops will be expensive, occasionally you can find deals on anchor optics clearance (though that info is years old, and to have to know what you're buying!).
You're almost always better off buying the cameras and sensors together, unless you have specific needs. Sadly, this isn't something where you can save money by doing it diy. Supply chains are good and overall demand is too high for deals outside the normal channels, I think.
Would love to be proven wrong, but I used to pay around with optics regularly and it was always more expensive than I liked. Cutting open photographic lenses was a common way to get fun glass for cheap... So getting cheaper glass is tough.