Observations of vector magnetic fields with a magneto-optic filter

We describe the use of the magneto-optic filter (MOF) to observe solar magnetic fields in the potassium line at 7699 Å. The filter has been used in the Big Bear video-magnetograph since 23 October. It gives a high sensitivity and dynamic range for longitudinal magnetic fields and enables us to measure transverse magnetic fields using the sigma component. Examples of the observations are presented.This paper was presented at the third meeting of the Solar Cycle Workshop, held in Sydney, Australia, January 9–13, 1989.NRC Senior Res. Fellow.