Exploration frequency and spatial sampling can affect the resolution of seismic imaging. Some factors have a great impact on the horizontal resolution, whereas other factors significantly influence the vertical resolution. How to quantify these effects still remains controversial for complex media. Most previous studies on seismic acquisition geometries focus on the horizontal resolution for seismic migration, but neglect to measure the vertical resolution especially in complex media. The conventional criteria for vertical resolution are based on the theory of geometric seismology with the assumption of a simple medium. Focal-beam analysis can provide comprehensive insight into the combined effects of acquisition geometries, band-limited frequencies, and complex media on vertical resolution. We define two parameters to quantify the vertical resolution of acquisition geometry: the main-lobe width (MLW) of a focal beam along the vertical direction and the ratio of its main-lobe amplitude to the total amplitude (RMT). MLW defines the vertical resolution to image the target, whereas RMT describes the clarity of the imaging. We evaluate examples of typical acquisition geometries to demonstrate how band-limited frequencies and acquisition parameters influence the vertical resolution, described in terms of MLW and RMT values. Comparisons of focal beams and classic criteria with increasing bandwidth and spatial sampling indicate that the MLW and RMT of focal beams can be more accurate to describe the vertical resolution of exploration seismology. Case studies of seismic migration with 3D seismic data from an oilfield in China demonstrate that the acquisition geometry with denser detectors has a larger value of RMT indicating more clarity in seismic imaging. Prior MLW and RMT analyses of acquisition geometry to predict the quality of acquired data sets can optimize the design of acquisition geometries before the implementation of seismic acquisition.