Once upon a Galaxy : A Journal of the Making of the Empire Strikes Back(1980)
A non fiction book by Alan Arnold
This book covers many aspects of the filming, and as Arnold has covered decades of movie making before writing this book, he is obviously genuinely impressed with the scale of the production. Good interviews with important members of the cast and crew; even includes Sir Alec Guiness. Especially illuminating chats with Lucas about the overall nine part structure of Star Wars. It's interesting to compare Lucas' initial ideas about the sequels and prequels with what was finally released. The highlight of the book is a transciption of a day spent following Irwin Kershner filming on the carbon freezing chamber set (Secrets revealed include the fact that Jeremy Bulloch as Boba Fett was actually desperate to use the lavatory throughout the whole day's shoot). As a collector of Star Wars related books, I have amassed over a hundred, but this remains my favourite.
Used availability for Alan Arnold's Once upon a Galaxy : A Journal of the Making of the Empire Strikes Back
1980 : UK Paperback