Fig. 4. (A) Thermogram of two mice, scaled for an 80° field of view with the animals 45 cm distant. Images were recorded at an air temperature of 15°C in sparse scrub habitat around midnight, following a mostly cloudy afternoon. (B–D) Image A convoluted with circular spread functions chosen to visualize the image along the optic axis of the facial pit. (E–G) Image A convoluted with elliptical spread functions to visualize imaging directly in front of the snake (right column). The _i indicated for each row is the aperture angle of a circular spread function (B–D), and the vertical _i of an elliptical spread function (E–G). The minor axis _i of the ellipse is half that of the vertical axis. The temperature contrast in these images is quite low, so for clarity we have assumed a larger pit and greater membrane sensitivity (color steps of 0.0005°C) than in Fig. 3. Note that, particularly for large _i (poor resolution), the warmest part of the image is a large, warm area of ground and not the mice.