Apertures and the notion of scale

Abstract

Observations are always done by integrating some physical property with a measurement device. Integration can be done over a spatial area, over an amount of time, over wavelengths etc. depending on the task of the physical measurement. For example, we can integrate the emitted or reflected light intensity of an object with a CCD (charge-coupled device) detector element in a digital camera, or a grain in the photographic emulsion in a film, or a photoreceptor in our eye. These 'devices' have a sensitive area, where the light is collected. This is the aperture for this measurement. Today's digital cameras have several million 'pixels' (picture elements), very small squares where the incoming light is integrated and transformed into an electrical signal. The size of such pixels/apertures determines the maximal sharpness of the resulting picture.