ABSTRACT
A number of terms loosely describe brightness in many texts, namely, luminosity, flux and magnitude. Luminosity relates to the total light energy output from a star; flux is a surface intensity, like an incident light reading in photography, falls off with distance. A telescope has a light-gathering advantage over the eye, easily imagined if people think of all the light pouring into the front of a telescope compared to that of the human iris. The magnitude of a star or galaxy in relation to the sky background and the sensitivity of the sensor are the key factors that affect the required exposure. The term sensor describes the light sensitive device that resides in a digital camera. The sensor still plays a pivotal role in the final resolution achievable in astrophotography. An imaging sensor has a grid of photosites of fixed pitch, typically in the range of 4-7 microns. The pitch of the photosite grid has a bearing upon image resolution.
