An optical center is the precise center of a lens or curved mirror. It is the point from which light rays diverge or converge. In a simple lens, the optical center is the midpoint between the two lens surfaces. In a compound lens, it is the point in the lens where the light rays passing through the lens converge to a single point.
The optical center of a book is the precise center of the book’s spine. It is the point from which the pages of the book diverge. The optical center of a page is the precise center of the page, from which the text and images on the page diverge.
The optical center of a printing plate is the precise center of the plate, from which the printing on the plate diverges. The optical center of a printing press is the precise center of the press, from which the printed images on the press diverge.
The optical center of a camera is the point in the lens where the light rays passing through the lens converge to a single point. The optical center of a projector is the point in the lens where the light rays passing through the lens converge to a single point.
The optical center can also be important from a production standpoint. For example, if a book is going to be bound using a method that requires the text to be glued down, then the optical center is the best place to start glueing the text down. This is because the optical center is the point on the spine where the pages are most likely to lay flat when the book is open, which makes it easier to apply the glue and get a good bond.
In general, the optical center is an important consideration when designing and producing books. It’s a good starting point for deciding things like page layout and binding method, and it’s also the most comfortable and aesthetically pleasing position for the text on the page.