Leica, on many of their lenses, notes their exact focal length. Can't say for sure if it's still being done, or if it's done on all focal lengths, but if you observe the markings on the lenses, and understand their meaning, you'll see that, for example, a nominal 50mm lens may actually be a 50.5mm, or 51mm. Different examples of the same lens have different focal lengths for numerous reasons, most of which I can't remember. So, my 50mm lens may have a slightly different focal length than another 50mm lens of the same manufacturer and model.
Shel > [Original Message] > From: graywolf <[EMAIL PROTECTED]> > Now we are actually getting into advertising claims. The tests I have seen show > the Vivitar 19mm as actually being 21mm. In fact, many lenes are only within > (10% or so) to their nominal focal lengths.
