Image side telecentric implies that the light rays impinging on the sensor arrive at right angles to the sensor surface and therefore are parallel to the optical axis. It is my opinion that in order for light on the image side of a lens to arrive parallel to the optical axis at the sensor the rear element of the lens must be equal to or (preferably) larger than the imaging surface. If smaller then the light rays will arrive at an angle. This leads to loss of light I think. This can be alleviated to some extent by an optical design that makes the effective aperture larger for off-axis light rays. It can also be alleviated by lenslets on the pixels but these can’t be optimized for all angles of incidence I think. I may be wrong on this … as in anything else here! Tele-centric is a well known definition of a lens system where the light rays arrive as a parallel bundle at the lens and exit in the same manner. This allows one to reproduce objects located at varying distances to the lens tat the same magnification. This is very useful in machine vision applications where comparisons between objects that are the same but not in same subject plane to be compared. But the field of view of a tele-centric lens is only as large at the lens. Not very practical for general photography. In any case, on the matter at hand, I would not hesitate in using an old lens on a digital camera. But I am not a lens designer or optical expert … just my observation. Andy
