Category Archives: Glossary

In physics, the focus describes the point in an optical system where the light rays intersect after passing through the optics. At this point, therefore, the information that previously ran parallel is centered and thus fully captured. Most often, the term focus is used to mean that something is displayed in optimum sharpness. Depending on the device and the system, the determination of the focus is done selectively, centrally or point by point.

In our systems, the focus is determined over the entire scan area by means of a contrast measurement. Where the contrast is highest is the optimum sharpness plane, i.e. the focus. By looking at the entire scan area, it is ensured that the edge areas are also optimally sharp and not just the center of the original.

A filter is usually a thin transparent sheet of glass or plastic that is attached to the front of the lens to alter the image as it is taken. There are filters with specific tasks to enhance the image, and there are filters that give photographers creative options, such as color or graduated filters. The former include infrared or UV filters, which ensure that neither UV nor infrared light passes through the optics and onto the sensor, adversely discoloring the image. Polarizing filters are also often useful, as they can prevent reflections and over-illumination. This prevents information loss in said areas.

An important field of application for filters is especially multispectral photography, since filters can be used to select a wide variety of light wavelengths and bring them specifically onto the sensor.

This term refers to a one-dimensional lens system that performs corrections in only one dimension. In book2net book scanners, the light system is usually located at the rear to avoid uncontrolled reflections into the optics caused by the curvature of the page. The LED light strip ideally illuminates the book in landscape format, but the different light paths on the surface result in different light intensities from back to front. A Fresnel lens compensates for this by directing more of the short beams to the back. We therefore use these lenses, adapted to specific applications, as fixed components of our high-quality systems.

The term folio derives from the Latin word “folium” (leaf) and refers to a traditional book format in which the size of the page is determined by the fact that the sheets used in the production of the book are folded only once. An unfolded sheet is called an atlas format, double folio or large folio.

However, because the size of the initial sheet and thus the final size of the book can vary, librarians have established their own guidelines for categorizing book formats. In Germany, modern library categorization follows the guidelines of the Deutsche Bibliothek in Frankfurt am Main, which date back to the Prussian Instructions (PI). Although this falls back on the old book format designations, it defines them exclusively by the height of the spine. Today, books with a spine height of 40-45 cm are classified as folio format. Books in folio format are marked with the abbreviation fol. or indicated as 2° (for 2 sheets).

World-famous examples of books in folio format are the Gutenberg Bible and Shakespeare’s First Folio of 1623, which was printed in 1,000 copies, bound in calfskin and sold for the price of 1 pound. Of course, only very wealthy people could afford this book.

In modern book printing, the folio format is mainly used for elaborate illustrated books or faithful reprints (facsimiles) of precious books from past times. The folio format is also popular for documenting anniversaries: many companies, corporations or institutes prefer to document their (success) history in large format. These volumes are then often published as hand-picked editions.

Since the classic folio format does not conform to any DIN standard, but lies between the formats DIN A2 and DIN A1, it also places special demands on scanning systems during digitization.