Instrumental factors affecting the fringe contrast in optical interferometers

Interference fringes are the prime observable quantity in astronomical optical and radio interferometers. To maximize the signal-to-noise ratio it is important to keep instrumental causes of fringe contrast decrease to a minimum. I discuss these and derive the tolerances to be, placed on them.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.