Soft x-ray microscopy offers high spatial and temporal resolution imaging with element specific magnetic contrast. As such, it is an ideal method for studying nanoscale spin dynamics, such as vortex core dynamics. At XM-1, the full field soft x-ray transmission microscope at the Advanced Light Source in Berkeley, a technique has been developed for pinpointing vortex dynamics without time resolution. In addition, a phase-locked setup has been used to conduct time resolved experiments of vortex core dynamics. The samples in this study were 100 nm thick, 2 mu m diameter Ni80Fe20 disks. Analysis of nontime resolved images suggested that resonant vortex core dynamics were excited by ac magnetic fields close to 340 MHz. This behavior was confirmed with time resolved imaging and gyrotropic motion of the vortex core was observed.