Originally Posted by rich
What is the delay time for your camera, between pressing the button and the shutter release?
Let's say it is 0.01 sec, a hundredth of a second. (I bet it's more than that really..)
So the combro registers the pellet passing the first sensor and instantly signals the camera to fire. No software delays at all. The shutter release sequence is initialised and 0.01 sec later a picture is taken.
Where is the pellet, that the combro detected? Well, it's doing roughly 800 feet a second, that is 8 feet in a hundredth of a second. 8 feet from the muzzle.
That's why you set it down range. The bit of kit I have allows you to dial in enough offset to capture the pellet further downrange. So you work out you want 50ms from it exiting the barrel, and it registers when the shot passes the sensor and fires the flash. Want it closer, less offset. Further, more.
But you don't use the shutter at all. The shutter is opened and kept open before the shot is released. The room is completely dark, no light, and the flash duration is effectively the shutter. The shutter closes later. But because the room is dark the camera only is exposed to light for the short duration of the flash being on.
You could shoot it on bulb, but the catch with digital cameras is that long exposure builds up heat and noise in the CCD, so ideally you look to limit the time the shutter is actually open. But in principle, it does nothing.