Q: What type of lenses do you offer?
A: We offer three types of c-mount lenses: standard, high performance, and megapixel lenses. Banner offers these lenses in the following focal lengths: 3.5, 4, 6.5, 8, 12, 16, 25, 35, 50 and 75 mm. We also have a 10-40mm zoom lens.
Q: What is a c-mount lens?
A: C-mount is a lens with a threaded mount. The threads have a major diameter of 1" and a pitch of 32 threads per inch. The flange focal distance is 0.69". C-mount lenses are used extensively with closed-circuit televisions, thus the lenses are readily available. Most machine vision sensors use a c-mount lens, although some use a slightly different standard, the cs-mount. The cs-mount lens is dimensionally the same as the c-mount except for the flange-to-focal plane distance (~0.49" for the cs-mount).
Q: What’s the difference between standard, high-performance, and megapixel lenses?
A: In a simple presence/absence application, a standard lens in the right focal length is a good choice. Standard lenses are inexpensive and are adequate for many applications. The high-performance and megapixel lenses are of better construction (metal housings rather than the plastic of the standard lenses) and most have the ability to adjust the aperture and to lock both the aperture and focus settings in place. By being able to adjust the aperture, you have more options as to where you place the part. By being able to lock the settings in place, you reduce the chance that vibration will eventually cause out-of-focus problems. When working with gauging and pattern matching applications, choose a megapixel lens because it offers less image distortion. Optically and mechanically, there is little difference between the high-performance and megapixel lenses, so we usually recommend the megapixel lenses.
Q: Can I use a standard lens on a high-resolution sensor?
A: Some standard lenses will work with a high-resolution sensor. In general, we recommend the use of a megapixel lens because the high-resolution sensor may highlight optical defects in a standard lens.
Q: What is “field of view?”
A: Field of view describes the area that is captured by the lens.
Q: What is “working distance?”
A: In a given lens setup, working distance describes the distance between the camera flange and the part under inspection.
Q: Why is focal length important?
A: Focal length relates the working distance to the size of the field of view (FOV). All lenses are specified using focal length. If you know your FOV and your working distance, you'll be able to determine what focal length lens you need.
Q: Does the imager size determine what lens I need?
A: Yes, the lens you choose must be capable of drawing an “image circle” as big or bigger than the imager chip of the vision sensor you are using.
Q: How does the size of my inspection area affect the lens I should choose?
A: The size of the inspection area (field of view) and the distance between the part and the camera (working distance) determine the “focal length” of lens. Focal length as you recall is used to specify a lens.
Download these charts for help finding a lens by FOV and imager size.
Q: How large an area can I inspect at close range?
A: In general, the widest angle lenses we sell have about a 1:1 relationship between the inspection area and the distance from the part to camera. This results in a 1 foot inspection area for 1 foot distance between the part and the sensor.