Figure 1: Schematic diagram of the lens.
Imaging lenses are also known as machine vision lenses, objective lenses, or simply lenses. For the sake of simplicity, in the following sections, imaging lenses will be simplified to lenses only.
The following terms explain each characteristic part of an imaging lens:
Focus Adjustment Ring:Turn this ring to change where the lens is best focused. The distance from the first surface to the object is called the working distance.
Aperture Aperture Adjustment Ring:Turning the aperture changes the size of the internal aperture of the lens, which changes the f-number (f) In addition to controlling the total amount of light that can pass through the lens, f has a number of other key effects on lens performance.
Finger Rotation:Used to temporarily lock the focus and/or aperture in place to prevent unwanted adjustments.
Lens Info:Lens information is marked on the lens barrel and usually gives the focal length, minimum f, part number, and lens manufacturer.
Working distance range:This is the specified working distance range that the lens can focus on. This is sometimes referred to as the object distance range.
f Active Tags:A marker on the lens barrel that specifies the position of the lens by turning the aperture adjustment ring at a specific f.
Filter thread:If the first element does not protrude from the barrel, a machine vision filter can be installed here. If the first element protrudes beyond the lens barrel, or if the lens is a wide-angle lens, an additional adapter may be required.
Camera Mount:This is where the lens passes through or is mounted on the camera. Typical stents are C-stents, F-stents, TFL-stents, and S-stents.
Rear protrusion:This is the distance at which the lens protrudes into the camera beyond the shoulder of the lens. Care should be taken to avoid interfering with the IR-cut filter or the electronics inside the camera mount.
First Surface:The first surface can be the first optical lens element protruding from the barrel or the barrel itself. The working distance is defined as the distance from this surface to the object.
The last surfaceThe final surface can be the last optical lens before the sensor, or it can be the lens holder itself.
Lens shoulder:This is the surface where the lens comes into contact with the camera flange.
Overall length:The total length of the lens is the distance from the first surface to the shoulder of the lens. Usually, the camera mount is not included as it will be attached to the camera.
Flange distance:The distance from the mounting shoulder to the image plane. For various mounting types, the distance between the lens and the camera is usually standardized to ensure compatibility.
Image Plane:The location where the lens forms the image, usually the camera sensor.