Keith wrote: > >Mark Erickson wrote: >> >> Bob wrote: >> >This has to be baloney. Light *has* to strike the sensor at an oblique >> angle >> >or an image will not be formed! Only light along the axis of the lens will >> >be perpendicular to the array, and of this light, only the ray on axis will >> >be perpendicular. >> >> Turns out that the light doesn't have to "strike the sensor at an oblique >> angle" to form an image. > >Turns out that in a practical world of consumer photography, it does. >If the object you're photographing is any larger than about 2", it does. >Read this excerpt form that first site below: > >"A telecentric lens "sees" a cylindrical tube of space of diameter equal >to that of the front lens element. It is limited to photographing >objects whose lateral dimensions do not exceed the diameter of the lens." > >The use for such a lens is so limited, it's pertinence in this >discussion is relegated to merely one of a curiosity. > >keith whaley
Keith, In practice I agree with you (how many of us have telecentric object-inspection lenses at home?). Thing is, Bob didn't qualify his statement with, "in a practical world of consumer photography." My bigger picture point is that in the practical world of modern multi-element lens design, lens designers can control the angle of arrival of light rays. I refer again to the retrofocus designs of very short focal length lenses (like the Pentax 15mm F3.5). If the Pentax lens designers are as good as we think they are, I'll bet that they're designing their latest lenses to accomodate the "quirks" of focal plane arrays. Anyway, thanks for actually reading the links and not just blasting away.... --Mark
