The Auto Sears 135mm f/2.8 lens is a telephoto lens designed for manual focus photography. It features an M42 screw mount, which was a popular mount type used in many vintage cameras, especially those from manufacturers like Pentax and Praktica.

Here are some key features of this lens:

1. Focal Length: The lens has a fixed focal length of 135mm, making it ideal for telephoto photography, such as portraits, wildlife, and sports.

2. Aperture: With a maximum aperture of f/2.8, this lens allows for good low-light performance and the ability to achieve shallow depth of field for subject isolation.

3. Manual Focus: As a manual focus lens, it requires the photographer to manually adjust the focus ring to achieve sharpness. This can provide precise control over focusing, but may require practice for those accustomed to autofocus lenses.

4. M42 Screw Mount: The M42 mount is a screw mount system, which means the lens is attached to the camera body by screwing it into place. This mount type was common on many cameras produced in the mid-20th century.

5. Vintage Leather Case: The lens comes with a vintage leather zip-up case, which adds to its nostalgic appeal and provides protection during storage and transport.