The Ricoh Theta Z1 of 2019 is the flagship of the Theta 360 line: twin 1-inch back-illuminated sensors — the largest in any consumer 360 camera at launch — behind folded f/2.1-5.6 optics in a slim candy-bar body.
It captures 23MP equirectangular stills with DNG raw support, 4K 360 video, has a small OLED status display, aperture control unusual for the category, and processes stitching in-camera with very little visible seam.
Its significance is professional: it became the default camera for estate agents and virtual-tour producers because the 1-inch sensors handle interiors and mixed light far better than the phone-sensor 360 cameras around it.
Used Z1s come in 19GB and 51GB storage variants — check which is offered since neither takes cards. Confirm both lenses are scratch-free (they protrude and take the hits) and that the battery, which is sealed, still holds a working charge.