![]() ![]() You can choose the proper lens according to the FOV listed on the below table. The formula here just gives you a basic idea about the lens. Note that all the calculation is based on the pinhole camera model, the real lens focus calculation is more complex the focal length will be different. From Figure 1 we can also calculate the focal length by the equation : f/d = h/H equals to f = d x (h/H). Provide the image sensor aspect ratio is 4:3, we can calculate the horizontal FOV = 75 degrees, and diagonal FOV = 94 degrees. So the vertical FOV θ = 2 x arctan(16/2/15) = 56 degree. ![]() Where H is the height of the QR code and equals to 16mm. ![]() If we want to use a full image plane to capture the QR code, from Figure 1 we can calculate the vertical FOV as 2 x arctan(H/2d). How we will study how to calculate the lens FOV and select a proper lens for QR code scanner application. Given there is a QR code scanner application, we have a 1/4″ image sensor, and the camera is 15mm away from the QR code, the QR code size is 16mm x 16mm. The angle of view can be calculated if the focal length and image size are known. Normally the angle of view is measured assuming a lens is focused at infinity. The FOV is also called angle of view which is the shooting range that can be viewed by the lens given specified image size. A zoom lens can change the size of an object appearing on the monitor to the extent specified by the zoom ratio. The zoom ratio is the ratio of the focal length at the telephoto end to that at the wide end. It is specific for zoom lenses rather than a fixed focus lens. For example, the fisheye lens LS-40180 can’t use any other lens holders except the mating lens holder designed specifically for this lens. Sometimes the lens comes with a very short focal length, so you should use a proper lens holder to match the back focal length of the lenses. Back Focal Lengthĭistance between the vertex of the rear element lens and image sensor. So the MOD parameter is specified for focusing on both close and far away objects. But you have to trade-off between the close object and far away object because only one can be well focused, the other end will be blurry. Sometimes, you can still focus the lens to very close object by manually focusing the lens. It is measured from the vertex of the front glass of the lens. Minimum object distance (M.O.D.) indicates how close the lens can be placed to the object for shooting. Figure 3 Image Circle Minimum Object Distance But when the lens optical format is larger than image sensor, the lens FOV will be reduced and when the lens optical format is smaller than image size there will be dark areas around the corners and some portion of the sensor area is not useful. If the lens optical format and image size doesn’t match, it also works. The lens optical format should match with the target image sensor like the leftmost photo in Figure3. The ratio of the length of the horizontal to vertical sides of a video image is called the aspect ratio, which is normally 4:3 (H:V) for a standard CCTV camera. In a CCTV camera, the imaging element has a rectangular sensor area (the image size) that detects the image produced within the image circle. Figure 1 Focal Length Image Size and Lens Optical FormatĪ lens produces images in the form of a circle, called the image circle, also known as the optical format. For a single thin lens, the focal length is equal to the distance between the center of the lens and the focal point. The distance between the principal point in the optical system and the focal point is referred to as the focal length. This point is the focal point of the lens. Parallel incident light transmitted into a convex lens converges to a point on the optical axis. ![]()
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