Need to convert very cheap vintage FF 50mm f/2.8 lens to work as 35mm lens for for APS-C, for having wider angle of view.
Its kind of works by simply placing lens closer to camera sensor (without adapter) however focus does not work.
I assume it can be made to focus if i change distance between lens elements?
What elements i need to space out to restore focus ability, can correct spacing be figured out mathematically?
I am not a tech savvy please explain in great details using plain language if possible.