A flasher sonar device includes a flasher that produces light output pulses along a flasher ring display based upon sonar returns. A user interface selects between a normal mode and a zoom mode. When the normal mode is selected, a controller drives the flasher to display a normal range. When the zoom mode is selected, the controller divides the normal range into a first range and a second range, compresses the first range into a compressed range, enlarges the second range into an enlarged range, and drives the flasher to display the enlarged range interleaved with the compressed range.