1. A Zoom Calibration accurate distance measurement method of using a variable field of view zoom lens having adjustable zoom magnification for accurate distance measurement between measurement objects at any position within said variable field of view, said Zoom Calibration method using reference objects as a measurement calibration standard, wherein said Zoom Calibration method comprises the steps of: (a) capturing a first measurement image of said measurement objects for which said accurate distance measurement is required using said zoom lens at an initial zoom magnification, said first measurement image further comprising a plethora of measurement pixel values representing said measurement objects in said first measurement image; (b) performing first measurement image signal processing on said measurement pixel values to determine accurate measurement pixel positions for each of said measurement objects in said first measurement image; (c) calculating a measurement pixel count as the number of pixels between said measurement pixel positions for said measurement objects in said first measurement image; (d) capturing a second reference image using said zoom lens without changing said initial zoom magnification of said zoom lens, said second reference image further comprising a plethora of reference pixel values representing said reference objects in said second reference image; (e) performing second reference image signal processing on said reference pixel values to determine accurate reference pixel positions for each of said reference objects in said second reference image; (f) calculating a reference pixel count as the number of pixels between said reference pixel positions corresponding to two reference objects that are present within said second reference image, said reference objects having a known reference dimension between them; (g) calculating the reference distance per pixel from said second reference image reference pixel count; and, (h) using said reference distance per pixel to determine said accurate distance measurement between said measurement objects in said first measurement image by performing a scaling operation on said measurement pixel count using the ratio of said known reference dimension and said reference distance per pixel.