The second source has been reading every ASC magazine from cover to cover and then reading them again.
The third source has been watching "The making of" docos that are often included on DVD's. And reading any books that come with the film. I now have a great and growing collection of these books mainly purchased used from Amazon and library surplus book sales.
The fourth source has been watching YouTube-style videos from web sites like Stan Winston School of Character Arts, BAFTA, Weta Workshop, etc and today Wolfcrow.
So here is a great video description from Wolfcrow of some of Roger Deakins methods. Roger is probably my favourite cinematographer.
And work by Christopher Nolan.
And focal lengths and lenses.