Here are some links to pdfs of some hard-to-find old manuals. As new manuals are added, they will be edited into this post.
These manuals are free for use and printing hard-copies by anyone; also, please feel free to copy the files for free distribution from your own website. I strongly believe that these out-of-date manuals should be widely disseminated for free, for all to use.
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Here are some links to some of the larger on-line free collections of microscope manuals and catalogs for older microscopes (1930-2000):
Bausch and Lomb:
https://vademecummicroscope.com/bl-manuals-and-catalogues/
Leitz:
http://microscope.database.free.fr/Welcome.html
American Optical, Spencer, Reichert:
http://user.xmission.com/~psneeley/Personal/Microscope.htm
Polarizing microscopes:
http://earth2geologists.net/Microscopes/index.htm
Olympus:
http://www.alanwood.net/photography/olympus/downloads.html#bh
and Carl Hunsinger's excellent Olympus repair trove:
https://drive.google.com/file/d/0B7ckZ6amci3tcVdXdnFYVDJSRW8/view
Zeiss:
http://roslistonastronomy.uk/category/microscopy/equipment-for-microscopy/microscope-manuals
All sorts:
http://www.science-info.net/docs/
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INDIVIDUAL MICROSCOPE MANUALS
Here is an English-language operating manual for the Reichert Univar, a 1970's-80's large, heavy, and sophisticated research microscope of its day. Reportedly, there were only about 300 of these made. I have one of these which I have been restoring to some semblance of its former glory. The manual was available on the internet only in German, so I translated it into English, reproduced it with all of its drawings, and also attached a Univar sales brochure to the end of the manual:
Reichert Univar Microscope Operating Instructions (English), V1.4:
https://drive.google.com/file/d/10DxbR9yXI4QQXK38fCUTFSXXXXo7vw6v/view?usp=sharing
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Bausch and Lomb Dynazoom Bench Metallograph Instructions:
https://www.dropbox.com/s/2112ra92dk949kv/B%26L%20Bench%20Metallograph%20manual?dl=0
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