Step 13: Bookholder: Introduction and Design Issues

Picture of Bookholder: Introduction and Design Issues
Congratulations on making the base for your book scanner.

One of the nastier problems in scanning books is that the "center" of the book shifts as you flip through the pages. I have a couple pictures with a very thick book that demonstrate this problem. Essentially, with books that have any thickness, the center "V" shape of the book moves left to right as you flip pages. However, the platen of our book scanner does not move. That means that we need whatever is holding the book to slide freely, to center it below the platen.

This is the main reason why the base of the book scanner must have a smooth surface, like melamine, plastic, or counter top. Things have to slide.
spamsickle6 years ago
I pulled the drawer supports out of a really nice desk someone had tossed -- sliders on ball bearings, with 3 metal extensions -- and was planning to use two of them for base sliders and one on the column to support the platen, so that the base would move smoothly from side to side, and the platen would rise smoothly straight up and down (no hinge). I may still do that, on my own version 2 book scanner, but for now I'm not sliding anything and I'm not attaching the platen to a center column. I'm just letting my book rest in a static base, and setting the platen on top of it. The problem is not just that the center of the book moves as you page through it. If you're working with a 3-inch book, on page 1 the left side of the book is three inches higher in the VST (cradle) and three inches further away from the camera than the left side will be on the last page of the book. And obviously, the right side is three inches closer and three inches lower on page 1 than it will be on the last page. Ideally, you want the camera on each side to get the same view of a page from the first page to the last. While "centering" the book in the platen helps some, it seems to me that the only way to insure a consistent view is to adopt the design that it looks to me like the bkrpr people have chosen, and have the cameras attached to the platen itself. In that configuration, the images seen by each camera should always be the same distance from the camera, and appear in the same position in the viewfinder, from the first page to the last. I went with 1/16 inch acrylic for the critical (page-pressing) planes of my platen, and while that seems to work fine with the absolute bare-bones implementation I'm working with now (no center column, no handle, just lay the platen in the book and shoot), there's no way 1/16 inch plastic is going to support a couple of cameras. So I'm thinking for version 2, I'll build a frame to hold the platen plastic, which will also be capable of holding cameras. In that design, the sliding cradle and a counter-weighted vertical-rise platen will make sense.