When I mount one of my lenses on my camera, my camera knows which apertures the lens has. So I ask my self: Why does my camera know that for example lens XY has a max. aperture of 2.8 and a min. aperture of 22. Are this informations stored in the lens?

For my case I use a Canon EOS.

  • \$\begingroup\$ Who? Do you mean "what"? \$\endgroup\$
    – dpollitt
    Commented Nov 26, 2013 at 3:28
  • 1
    \$\begingroup\$ @dpollitt - My camera has a soul, it has feelings, and if I treat it right it gives me good pictures. It sure is a "who" ;) \$\endgroup\$ Commented Nov 26, 2013 at 5:43
  • \$\begingroup\$ @dpollitt: of course what, but [at]dpollitt: you are absolutely right :-D \$\endgroup\$
    – Micha
    Commented Nov 26, 2013 at 6:13

4 Answers 4


It all depends on exactly which camera and which lens you are considering.

In most cases when you use a modern digital camera and lens that are both made by the same manufacturer the lens reports this information to the camera, along with other identifying information that tells the camera things such as the specific model of the lens, the current focal length for a zoom lens, and sometimes even the lens' serial number. In the case of your Canon EOS camera, any Canon EF or EF-S lens will report that and more to the camera body. Most modern third party lenses also are "chipped" to speak the language of the camera brand upon which they are designed to mount.

Although not the case with the Canon EOS system, some older lenses that will still mount on a much newer camera from the same manufacturer do not communicate with the camera body and the aperture range the lens is capable of is not indicated by the camera. In some situations, the camera uses mechanical linkage to stop down the lens. In other cases the aperture is set on the lens itself and the camera may or may not be able to detect the aperture setting. If the camera can not detect the setting, then shooting must be done in Manual exposure mode. Sometimes metering can be accomplished with the lens stopped down, sometimes the result of metering must be manually adjusted to compensate for the difference between metering when the aperture is wide open and the aperture used when the diaphragm is stopped down and the shutter is open.

  • \$\begingroup\$ very good answer, I have an edge case to add. The Tamron adaptall-2 lenses have no chip, but they have a series of mechanical linkages which allows the electronic version of the mount to determine max/min aperture and report to the camera correctly. (I have a couple of these and a Pentax KA mount which works nicely on my K5-II) \$\endgroup\$ Commented Aug 9, 2017 at 7:59

Yes, stored in lens.

Camera query this info through the "CPU contacts" to lens, and the lens provide that info.

The mount (e.g. F-mount) defines the language of their communication.


Yes, a lens identifies itself to the camera body. Aperture range and focal length are transmitted to camera as well as currently useable max aperture in case of a variable aperture zoom lens.

A lens also tries to tell the camera what it exactly is, and most of the time this works out well when both the lens and camera come from the same manufacturer.

Third party lenses are sometimes incorrectly recognized or missed altogether. However, apertures and focal lengths are transmitted correctly even then. Old manual lenses may lack the electronics to do this, which may lead camera body to inform the owner that "no lens attached".



The lens has a mainboard and the camera body has a mainboard. Mainboards consist of processors (CPUs), inputs/outputs and control lines.

The lens will have data of the lens in it, such as min/max aperture.

The lens and body communicate to each other to auto-focus, set the aperture and determine the focal length (at a rough guide).

For the focal length, generally the lens has a set of contact brushes which slide across contacts on the mainboard. At different points it will indicate the focal length and the lens will communicate this to the body when the photo is taken.

When it's auto-focussing, it needs as much light as possible. Generally if it's a f1.8 lens and you set it to f5.6, the body will set it to f1.8 during the auto-focus process and then once it's in focus, the body will set it to f5.6 and take the photo.

Of course, as has been stated, things change when your not using proprietary products.


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