There are many types of commercial photo copying machines designed to make paper negatives or direct paper positives without the aid of a camera. These range from the costly rotary printers used in industry to the cylindrical type used in offices. Most of these produce excellent copies of single sheets; but with many of them there is considerable difficulty in making copies from books, the printing usually being blurred and the copy unevenly shaded. The physical pressure required to make perfect contact during exposure often damages larger books.