A previous thread here has prompted this new one discussing the use of on camera flash, and the selection of slower hand held shutter speeds (AKA, "dragging the shutter). Some people persist in questioning being able to get sharp images of subjects while hand holding at 1/20th (or even less, depending on the level of ambient light), when using a modern flash. This is actually a fascinating subject, with it's own roots in photographic history. The principle of using a short burst of light to freeze the subject started early on, but truly came into it's own when Dr. Harold Edgerton of M.I.T., developed the Xenon flash tube ... which is the basis of today's modern flash that we all use. This short burst of intense light is what allows us to make a photograph in darker ambient conditions using a slower shutter speed than we'd normally be able to hand-hold ... because it is the duration of the flash that does the freezing, not the shutter speed of the camera. It is said that modern flashes for on camera use have durations from about 1/1000th of a second when used at full power/duration, to 1/10,000, depending on how much light is needed. Powerful studio strobes are often a bit less when used at full power (like 1/800th). So, in darker conditions like we face at a reception, you can drag the shutter to pick up more ambient background light, while the short duration of the flash lights the subject at 1/1000th of a second. To exaggerate the idea, enter a pitch dark room, set the camera's shutter speed to 1/10th of a second, pre-focus the camera and have a person jump in the air as you fire a shot. They will be sharp. In a crude way, this is exactly how Edgerton made photos of a bullet piercing an apple ... not with shutter speed, but with flash duration (and the help of sophisticated triggering equipment ; -) Google High Speed Photography for an interesting visit to the world of flash use.