depth-of-field preview button
/ˈdɛpθɒvfˈiːld ˈpɹiːvjuː ˈbʌtən/
n
English · depth-of-field preview button中文 · 景深预览按钮Español · botón de previsionado de profundidad de campoFrançais · vérification de la profondeur de champ
意味：Button that closes the diaphragm so that the relative clarity of various depths can be seen through the viewfinder.