I browsed around the net and found some references to Corporate Authorship that states that such material is copyright-protected for 75 years - placing, today, material produced in or before 1931 in the public domain. What are the copyright rules on older, printed manuals such as old Leica manuals from the 1930's? Are you allowed to freely copy and distribute them or are you in violation of copyright rules by doing so? If they are not distributed for profit - is it possible to claim 'fair use'? Now, I believe all print material created prior to 1923 is all considered part of public domain but there seems to be a grey area for items created between 19 (when the Copyright Term Extension Act kicks into effect).