The depth of field of the bar code gun is related to the density of the bar code to be scanned. For example, a scanner scans a 10 mil density bar code. It can be scanned by a scanner recently. The farthest distance can be 20 cm from the scanner. Then on the 10 mil bar code. Scanner depth of field is 0-20CM
The same gun scans a 5 mil density barcode, which can only be scanned from the scanner to 10CM. The depth of field of this scanner is 5-10.
There are also some barcodes that can be swept from 5CM to 8CM from the gun, then the depth of field for this barcode is 5-8CM