Daniel Reetz, the founder of the DIY Book Scanner community, has recently started making videos of prototyping and shop tips. If you are tinkering with a book scanner (or any other project) in your home shop, these tips will come in handy. https://www.youtube.com/channel/UCn0gq8 ... g_8K1nfInQ

Is there an optimal angle of view of the camera?

Everything camera related. Includes triggers, batteries, power supplies, flatbeds and sheet-feeding scanners, too.
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L.Willms
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Is there an optimal angle of view of the camera?

Post by L.Willms » 05 May 2018, 07:01

Is there an optimal angle of view of the camera?

Consider a rectilinear lens in a camera used to photograph an object at a distance S1, and forming an image that just barely fits in the dimension, d, of the frame (the film or image sensor), where F is meant to be the focal length, which then results in α being the angle of view.

Image
From en.wikipedia.org/wiki/Angle_of_view, where formulas are explained.

An online calculator is found at http://www.vision-doctor.com/en/optical ... tions.html

This question had already been touched in topics Camera settings for book scanning and How to get desired dpi?

duerig
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Re: Is there an optimal angle of view of the camera?

Post by duerig » 10 May 2018, 12:12

There are two other constraints here.

First, there will be a maximum and minimum distance from the camera which can remain in focus. The camera must be in this range of distance from the page.

Second, since the page must be well-lit, the camera needs to be at a sufficient distance away so that it won't cast shadows or have other lighting reflection issues. With scanners that capture both pages at once, the camera has to be even further away because it might cast a shadow on the opposing page. This is very specific to the exact scanning rig setup, though.

I ran into many of the same issues that you did when I was looking into prime lenses. In theory a prime lens yields better quality (less distortion) than a zoom lens. But unlike a zoom lens, you don't get to adjust the angle of view on the camera. So actually making these calculations becomes much more important.

It might be that the best way to deal with this issue if you want to use a prime lens or a wide angle lens is to work backwards. Start with a platen size and distance that the camera has to be (possibly picking a platen size to stay within a good focal distance). Then design the scanning rig around it, positioning the lights after the fact in a way that won't cast shadows.

L.Willms
Posts: 129
Joined: 21 Sep 2016, 10:51
E-book readers owned: Tolino Shine
Country: Germany
Location: Frankfurt/Main, Germany

Re: Is there an optimal angle of view of the camera?

Post by L.Willms » 11 May 2018, 17:05

Thanks!

BillGill
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Re: Is there an optimal angle of view of the camera?

Post by BillGill » 12 May 2018, 09:33

In regard to lighting, I find that I get the best results if I have the light source at a very low angle with respect to the document being scanned. For this to work you need a bright source. I am currently using 2 500 Lumen daylight floods set at right angle to the page (one on each side). The problem with this is that the lights can get in the way of handling the book. For the traditional 2 page scanner with the V-shaped platen it is very difficult. I resolved it by using a single page scanner in an inverted platen configuration. See viewtopic.php?f=14&t=3467. This also allows the camera to be mounted at the correct distance to scan each page without zooming the camera.

Bill Gill

L.Willms
Posts: 129
Joined: 21 Sep 2016, 10:51
E-book readers owned: Tolino Shine
Country: Germany
Location: Frankfurt/Main, Germany

Re: Is there an optimal angle of view of the camera?

Post by L.Willms » 12 May 2018, 16:06

After writing my initial post, I came to the conclusion that the best is a vertical look on the page, a 90° view or a 0° angle of view. That's what a scanner does with its moving bar of sensors.

But when using a camera, additional constraints have to be considered, as duerig explained. Theoretically, the maximum distance of the camera from the page would be called for, but that is not possible. So an optimum has to be found, which is always a compromise.

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