We investigated an edge response of an extended object in a turbulent atmosphere using imagery data acquired with a double-waveband passive imaging system operating in the visible IR wavebands and an actively illuminated optical sensor. We made two findings. We found that the edge response of an extended object is independent of an exposure time, and an atmospheric tilt does not contribute to the image blur of an extended object. In addition, we found that turbulence-induced image blur for an extended object reduces, not increases, with the imager diameter. Therefore, one can reduce the turbulence-induced image blur for an extended object reduces, not increases, with the imager diameter. Therefore, one can reduce the turbulence-induced blur by increasing aperture diameter of an imaging lens. Both findings contradict the predictions of the conventional imaging theory, suggesting that the conventional theory is not applicable to extended anisoplanatic objects. We provided physical interpretation for the results obtained. In addition, we discussed the mitigation techniques that allow us to reduce both turbulence-induced image blur and edge waviness in optical images.