Laowa's extreme ultra-wide for Sony — the 9mm f/5.6 W-Dreamer, same as ID 3521.
The Laowa 9mm f/5.6 FF II W-Dreamer is an ultra-wide manual-focus prime from Venus Optics (Laowa) for Sony FE full-frame E-mount, claiming to be the world's widest rectilinear full-frame lens at 9mm. The FF II designation indicates the second full-frame version, and W-Dreamer is Laowa's brand for extreme ultra-wide designs.
The lens delivers 9mm at f/5.6 maximum aperture with a rectilinear (non-fisheye) optical design maintaining straight lines, manual focus, manual aperture, Sony FE electronic contacts for EXIF, and full-frame coverage with an approximately 130-degree diagonal field of view.
The 9mm rectilinear on full-frame is the widest distortion-free option available for Sony FE — there are essentially no direct competitors at this focal length with rectilinear correction. It enables photography of interiors, architecture, and landscapes at an extreme angle of view without the barrel distortion of a fisheye design.
Inspect the extreme front element for coating damage — it is highly vulnerable at 9mm. Test corner sharpness at f/5.6 on a full-frame sensor, as rectilinear ultra-wides show the most demanding corner performance requirements. Verify no vignetting. Check focus ring operation.