你用的胶卷感光度是多少？ What's the speed of the film you're using?
光度计用来测量光的性质、尤其是光的强度和通量的仪器 An instrument for measuring a property of light, especially luminous intensity or flux.
光度视网膜亮度单位，相当于每平方米有一烛光亮度的表面，通过一平方毫米的瞳孔区域，到达视网膜的光线数量 A unit of retinal illumination, equal to the amount of light that reaches the retina through 1 square millimeter of pupil area from a surface having a brightness of 1 candela per square meter.
北极星第二星的光度中的一颗星，位于小熊星座把柄的末端，几乎位于北天极 A star of the second magnitude, at the end of the handle of the Little Dipper and almost at the north celestial pole.
