http://www.moosepeterson.com/techtips/flash.html

FYI

“To illustrate this point, let's look at the rate of light fall off for the SB-24/ 25/26 (which are all the same). Using film with an ISO of 125, a subject at 60 feet can be properly exposed at f/2.8. At f/4 it drops to 40 feet, f/5.6 to 30 feet, f/8 to 20 feet, f/11 to 15 feet, f/16 to 10 feet and at f/22 to a mere 7feet. That's an incredible drop off in power in the space of a few feet. But it's important and a fact of life we must work with. (This assumes the subject is an 18% gray and does not take into account whether the subject is white or black because either case can radically change the needed f/stop.)

You should also note from this point the relationship between flash-to-subject distance and aperture. Aperture is our other means of regulating the exposure. Using the information in the above example, if the subject is 30 feet away the proper exposure is f/5.6. But if our subject is white and at that same distance, we would probably want to open the aperture up to f/4 to record the subject as white. And if the subject is dark, we would want to probably close up one stop to f/8. During this whole exercise, the flash-to-subject distance never changed. We changed exposure strictly by changing the f/stop.”

所有跟帖： 

• 我也在学习， 但是有几个概念要清楚。 -Suijin- ♂ (309 bytes) () 01/19/2014 postreply 20:12:08

• 我准备用wireless trigger同时引闪两个闪光灯照舞台片，比较低光，可用同样参数？ -Gsong- ♂ (0 bytes) () 01/19/2014 postreply 20:25:17

• 闪光灯离人多远啊？　 -Suijin- ♂ (294 bytes) () 01/19/2014 postreply 20:35:16

• 闪光灯离演员至少4米，拍摄者应15米以外。不用闪光灯，片子能亮吗？ -Gsong- ♂ (0 bytes) () 01/19/2014 postreply 20:55:40

• ４米好远啊。即使够得着，闪光效果也很不好啊。　 -Suijin- ♂ (31 bytes) () 01/19/2014 postreply 21:08:01

• 那我还是跑到舞台最前面， 用35mm f1.8加高ISO做吧，或闪光灯再近点 -Gsong- ♂ (56 bytes) () 01/19/2014 postreply 21:14:07