The Canon EF 8-15mm f/4L Fisheye USM Lens is a specialized fisheye lens designed for Canon EOS DSLR cameras with EF lens mounts. This lens is part of Canon's "L-series" lineup, which is known for its high-quality optics and build quality. Here are some key features and characteristics of this lens:

Focal Length: The lens covers a focal length range of 8mm to 15mm, making it highly versatile for capturing ultra-wide-angle and circular fisheye images.
Aperture: It has a maximum aperture of f/4, which allows for good low-light performance and control over depth of field.
Fisheye Distortion: This lens is a fisheye lens, which means it produces highly distorted, barrel-like images with an extremely wide field of view. This can create unique and dramatic visual effects, but it's not ideal for rectilinear or straight-line architectural photography.
L-series Build Quality: As an L-series lens, it features a robust and weather-sealed design. This means it's resistant to dust and moisture, making it suitable for use in a variety of shooting conditions.
Ultra Sonic Motor (USM): The lens features Canon's Ultrasonic Motor (USM) for fast and quiet autofocus, making it suitable for both photography and videography.
Zoom Range: This lens offers both circular fisheye and full-frame fisheye perspectives, allowing you to capture various creative shots.
Compatibility: The Canon EF 8-15mm f/4L Fisheye USM Lens is designed for full-frame Canon EOS cameras, but it can also be used on APS-C sensor cameras. However, it may produce a circular fisheye effect on APS-C sensors.
Front Lens Element: It has a protruding front lens element, so you need to be careful when using filters or adding lens protection to avoid vignetting in your shots.

This lens is popular among photographers looking to create unique and artistic images with a fisheye perspective. It's commonly used in creative and specialized photography, such as capturing dramatic landscapes, architecture, and other creative visual effects. However, it may not be suitable for everyday or traditional photography due to its extreme distortion.

A creative option for photographers, the EF 8-15mm f/4L Fisheye USM is a versatile lens that provides a 180-degree circular field of view on full frame cameras at 8 mm, opening to an ultra-wide fisheye view at 15 mm. Ideal for creative shooting with artistic results, distorting the angle of view lets you get more of the landscape within the frame or distort your subject for unique visual effects. Part of the Canon professional L-series flagship range, this lens is designed for robust handling and resistant to dust and moisture.

Benefits

A versatile fisheye zoom lens offering a choice of full frame or circular creative images
Fast and quiet autofocus with a ring USM (Ultrasonic motor) using ultrasonic frequency vibrations
Fixed f/4 aperture for consistent exposure
Reduce ghosting and flare with Subwavelength structure coating
Part of the Canon professional L-series flagship range, its designed for robust handling and resistant to dust and moisture
Compatible with all Canon DSLR cameras and EOS-M mirrorless cameras with an EF-EOS M Mount adapter