Yasuhara Madoka 180 7.3mm f/4 circular fisheye

The Yasuhara Madoka 180 7.3mm f/4 is an unusual lens. It is one of the very few circular fisheye lenses, and the only one, that I know of at this time, for a mirrorless camera. A circular fisheye lens is one that projects a circular image on the centre of the imaging sensor, usually with 180° coverage. This is in contrast to full frame fisheye lenses, which fills the whole imaging sensor, and generally feature 180° coverage across the diagonal only, see the illustration below:

The specifications are given by the name of the lens: The lens projects an image circle of 180° field of view, and has a maximum aperture of f/4. The focal length is 7.3mm. This is pretty much all you need to know about a fisheye lens. I'll get back to the significance of the focal length later.

To understand just how wide this lens is, I compare it with the 16-50mm f/3.5-5.6 kit zoom lens at 16mm, which is already quite wide. The images are taken on a tripod at exactly the same spot, using the Sony NEX-3N:

Sony E 16-50mm f3.5-5.6 OSS @ 16mm f/8	Yasuhara Madoka 180 @ f/8

Physical appearance

The lens appears fairly solidly made, with a metal construction in a matte black finish. The supplied lens cover is plastic, and fits over the lens by means of friction, which works just fine: