ABSTRACT
Copying does offer the opportunity of modifying size, contrast and colour balance of the original for improvement, effect or storage. Various specific systems are used for general purpose or specific copying needs, but they share some common optical requirements. Copying a large original at same-size means that a large format is required, and special transportable cameras have been made to copy originals in situ, e.g. murals and frescoes, on to self-developing colour materials. Freedom from reflections does not guarantee perfect illumination for copying. For alignment of temporary copying arrangements, the placing of a suitable grid or reticle in the focal place and projection on to the copyboard allows accurate alignment by measurement of the dimensions of the image. Twin-lens reflex camera suffers from both parallax and framing errors at close distances due to its dual-lens system, but parallax correction devices may be used to elevate the taking lens into the position of the viewing lens.
