A "lens ring" can refer to several different types of rings associated with lenses, primarily in the context of photography and industrial sealing:

1. Lens Ring (Photography):

• Aperture Ring:

  Found on manual lenses, this ring controls the size of the lens's aperture (the opening that lets light in), allowing the photographer to adjust the depth of field and exposure. 

• Focus Ring:

  Present on virtually all lenses, this ring allows the photographer to manually adjust the focus point of the lens. 

• Zoom Ring:

  Found on zoom lenses, this ring allows the photographer to change the focal length of the lens, zooming in or out. 

• Filter Thread:

  A ring located at the front of the lens that allows you to attach screw-on filters, such as UV, ND, or polarizing filters. 

2. Lens Ring Gasket (Industrial):

• High-Pressure Seal:

  These gaskets are used in high-pressure applications, like piping systems and pressure vessel heads, to create a strong, metal-to-metal seal.