The scanner is close to the barcode and can't read

If we can't accurately grasp the distance between the barcode scanner and the barcode, it is easy to "can't scan the barcode" or "need to scan several times to scan it". At this time, we believe that many users will suspect that there is something wrong with the scanner, or blame the poor scanning performance of the scanner. This is a wrong understanding.
So what is the reason? It involves a professional term for a barcode scanner, called the best working distance. Bar code scanner has an optimal working distance for the highest resolution performance, which is the so-called focal length. The resolution of the barcode scanner is adjusted according to the focal length, which can also be said to be the ability of the barcode scanner to decode the narrowest bar width. For this reason, if the distance between the barcode scanner and the barcode changes, the narrow bars and blank areas of the barcode may not be read correctly, so there will be a phenomenon that the barcode scanner cannot scan the barcode.Let's take a look at the differences between the red light barcode scanner and the laser barcode scanner.
1) CCD barcode scanner:
In the camera, based on the CCD barcode scanner, the barcode image on the red light image sensor is captured through the lens. Therefore, if the captured image is out of focus or the barcode is blurred, it will be more difficult to read the barcode.
2) Laser barcode scanner:
The spot diameter is the smallest at the focal length. At positions larger or smaller than the focal length, the spot diameter becomes larger, making it impossible to recognize barcodes/blank areas. Resolution is highest at the focal length position. So the barcode scanner may recognize uneven printing density, dust, and scratches as part of the barcode. So when reading barcodes with low printing accuracy or fibers on the background (such as cardboard), we need to pay attention to matching the focal length and narrow bar width.