Chlorophyll, the green pigment present in the oak leaves, absorbs light, assuring the conversion of CO2 + H2O in O2 and carbohydrates needed to growth. In autumn time, low temperatures reduce chlorophyll synthesis, remaining in leaves another pigment – carotene, which gives them the yellow color.
The image was taken using a Nikon D40X camera with Nikon 55-200mm VR AF-S f/4-5.6G ED lens and these settings: exposure time – 1/250, focal length – 55 mm, ISO – 200, F- number – 5.