The Jena
ThULB (Thüringer Universiotäts- und Landesbibliothek) has a fine search interface for its "historische Bestände" (more ancient holdings) at
http://archive.thulb.uni-jena.de/hisbest/editor_form_search-cbu.xml and the collection of "philosophica" (not all of which are tagged there as philosopphy items) in the
Bibliotheca electoralis there is remarkable, rich, quite worth to have a look at. And many (or even more) of the items are digitised. And the resolution (where checked) is decent, and so is the file format (tiff)
That's the good news.
The less good news is that the items digitised are available only as single page tiffs (though by clicking on the "T" symbol ("Übersicht (technische Metadaten)") when viewing an item you can get a frame with links to the single images, so that you can use some tool to download them. But you have to have it: apparently there's no link to a ZIP archive or something like that with all of the images from a certain item.
A yet major problem is that the server -as of now - seems to be extremely slow. (I checked with
tracert: The
routes from Munich to Jena (and vice versa)
are fast; so the problem seems to be connected to the server. Once this is resolved and I learned about such resolution: expect me to point to quite a number of items in this collection here in
Web4Ren Forum (W4RF).
Found thanks to a note by Klaus Graf on Facebook.