Parts of a Camera Lens – Elements, Aperture, Rings and Mount

All 9 parts on the diagram

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Start here: 5 main parts 4

Front element The first piece of glass that light passes through. It is one of the most important to the picture.
Aperture diaphragm A ring of blades, also called the iris. It opens and closes to control how much light passes. A wider aperture lets in more.
Zoom ring Turned to change the focal length. It moves elements inside to zoom in or out.
Lens mount Locks the lens onto the camera body. It is the metal ring at the back.

From the side: 7 3

Filter thread A screw thread round the front of the barrel. Filters screw on here.
Lens elements The lens elements: the pieces of glass inside. A zoom lens can have more than 20, some cemented together in groups.
Focusing ring Turned to focus by hand. This moves elements inside the lens.

The back: 2 2

Bayonet lugs Tabs on the mount that turn into slots on the camera. They lock the lens in with a twist.
Electrical contacts They connect the lens to the camera body when it is mounted.

How this list was compiled: Read 2026-09-27. (1) Wikipedia, Camera lens, https://en.wikipedia.org/wiki/Camera_lens : a compound lens of several elements, from one to over 20 in complex zooms, some cemented together in groups; the front element is critical to the whole assembly; focusing moves the lens or elements within it; an iris diaphragm adjusts the aperture to regulate the light; zoom lenses change focal length as internal elements move, usually by turning the barrel; detachable lenses fix to the camera with a lens mount holding mechanical linkages and often electrical contacts. (2) Canon EF-S 18-55mm f/3.5-5.6 IS lens instructions, https://archive.org/details/manualsbase-id-42698 : lens mount index, contacts, focusing ring, zoom ring, filter mounting thread, lens cap and dust cap. Licence: own work

The drawing: Drawn for this site on 2026-10-05 by script, from plain geometry: one standard zoom lens held as a set of profiles (distance along the axis, radius), shown from the side with the near side cut away to about halfway below the axis, and end on from the back with the lugs in the same places. Every glass surface is an arc of a circle. Own work; nothing is traced or copied. The layout of a cut lens and of a mount was checked by eye against photographs of cutaway lenses on Wikimedia Commons. Licence: own work

How it works

These are the parts of a camera lens on an interchangeable zoom lens: side-on with the top half cut away to show the glass, then the mount from the back. Start with the 5 main parts.

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The glass

Light enters through the front element and passes through the other lens elements, several pieces of glass that work together. The aperture diaphragm among them opens and closes to let in more or less light.

The outside

Turn the zoom ring to zoom and the focusing ring to focus; both move elements inside. Filters screw into the filter thread at the front. At the back, the mount's bayonet lugs lock the lens on, and the contacts connect it to the camera body.

A smaller f-number means a wider aperture, which lets in more light and gives less depth of field.

Questions and answers

What is a lens element?

One piece of glass inside a lens. Camera lenses use several, from one in a simple box camera to over 20 in a complex zoom, some cemented together in groups.

What does the aperture do in a camera lens?

The aperture diaphragm, a ring of blades, opens and closes to control how much light reaches the sensor. A wider aperture also blurs the background more.

What are the metal dots on the back of a lens?

Electrical contacts. With the mechanical linkages in the mount, they connect the lens to the camera body, so the two can work together when the lens is on.