Size Constancy: A perceptual distortion that causes a mismatch between how we see an image and how a lens records it.
Check out http://www.psychologie.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/size_constancy.html for an explaination.
Remember back to the hand experiment. Place both your hands out in front of you and pull one of them back towards your face. Do they still appear to be the same size? Now place the nearest hand to your face on top the the father hand. Now what do you think? This kind of illusion can create a discrepancy between what we think we see when taking a photo, and what develops on film.
