this is doing my head in.. http://www.lhup.edu/~dsimanek/scenario/labman3/telecen.htm you have *got* to see the image on this page using a real telecentric lens - the distant part of the object appears larger than the close part ! "When this experiment was written, back in 1972, telecentric lens systems were considered somewhat "exotic". But now (2006) they are finding new applications in astronomy, machine imaging applications and industrial quality control measurements. Imaging arrays are generally small compared to the area of photographic film images, and their performance is very much improved when all light rays impinge normally (perpendicular to) the array surface. This is due to the three dimensional nature of the sensor elements, and the fact that some incorporate tiny color filters above each sensor element. The entire sensor array is smaller than the diameter of the typical film camera lens. So it is quite practical to use a system telecentric on the image side to ensure that condition of normal incidence. Now such a system is even used in digital cameras (for example the Nikon Coolpix)." I wonder if the author is swallowing the Nikon marketing or whether this is truly the case - has anyone noticed the effect described and clearly visible in the image? especially when taking this into account "Q: Why don't you state the focal lengths of your lenses? A: Unlike other telecentric lenses that have real focal lengths, such as 55mm for one popular model, Double Telecentric lenses have infinite focal lengths. Optical engineers call this being afocal. It's why the Double Telecentric design can have much larger Magnification Depth of Field." from http://www.lw4u.com/mvh-machine-vision-FAQ.htm there's also this http://www.edmundoptics.com/TechSupport/DisplayArticle.cfm?articleid=239
