A circular fisheye lens is a type of fisheye lens that produces a circular image with extreme distortion, typically covering a 180-degree angle of view. The circular fisheye lens captures a full circular image with a black border surrounding the circular frame, giving it a distinct circular appearance. It is commonly used in small cameras for security, surveillance, and monitoring applications, where a wide field of view is required to capture a large area. M12 circular fisheye lenses are available in different focal lengths, aperture sizes, and resolutions, and are typically made of high-quality glass or plastic materials. Some popular examples of M12 circular fisheye lenses include the 1.8mm M12 circular fisheye lens for Raspberry Pi cameras and the 1.56mm M12 circular fisheye lens for GoPro Hero 4/5 cameras.