Letters

[ Editor's Note: In our January issue, we published a letter in which OSA Fellow H.S. Kwok asked OPN readers to help him solve an optics puzzle. Kwok wondered how a window in a garden in Guangdong, China, could convert an outdoor scene from summer to winter to autumn, depending on the position of multiple panes of blue-tinted glass. Kwok's first photo was of the original summer scene of green trees and a stone sculpture, with no filters on the window. The second photo captured the window with one blue filter over it; the image was tinted blue and the tops of the surfaces in the scene were a wintery white. The third image, of the window with two blue filters, made the leaves on the trees turn red. To view the photos and read Kwok's original puzzle, please visit the OPN blog. We received many responses, which are included here. ]