Harley Kelsey wrote: > > You can get blurred pictures using digital cameras because there is a > delay after you press the shutter, while the camera adjusts exposure, > etc.
Yes and no... The blurring isn't because of any delay between when you push the button and when the image is captured - that's just why the locomotive has moved half way out of frame by the time the photo is taken. The blurring comes from the length of time the shutter is open to allow enough light onto the chip. It's very much like using a slow ASA film. If you're shooting with ASA 64 film on a bright sunny day, then at f16, a properly exposed photo would need a shutter speed of approximately 1/60th of a second. Shooting the same film inside with less light would require a longer shutter speed or wider aperture, or both. So, how does this relate to digital photography? The same principles hold true. What we need to figure out is how our camera's light sensitivity relates to film speed. My camera (Minolta S404) has a "base" speed equivalent to ASA 64. It has two aperture sizes - f3, and f6.7. On a bright sunny day, using its default sensitivity setting and widest aperture, I can get away with shutter speeds on the order of 1/500. If I were to go to the smaller (f6.7) setting, my maximum shutter speed would decrease to 1/250. Great for most applications shooting outside in bright light. For "typical" shooting conditions, though, with overcast skies or indoor lighting, our cameras need to get more light to the chip. On my camera, I can "increase" the effective ASA up to 400. This is the same thing as turning up the gain on a video camera. Your images will be noticeably grainier the higher you increase the sensitivity. (Film is much the same way - the faster the speed, the grainier the film.) You can only do that up to a point, though. Eventually, the camera is just going to need to keep the shutter open for longer periods of time to make sure enough light gets to the chip. When shooting moving live steam locos, this increased time is our worst enemy. Let's take a 1:20 locomotive traveling at 40 scale mph. (2 real mph.) That means in one second, the locomotive travels 2.93 feet. (Hey - I could use an Aster as an example.<grin>) If we use a shutter speed of 1/60, then our locomotive travels 0.6" during the exposure. At the distances typical of model photographs, that distance becomes very noticeable, and the locomotive will be blurry. At 1/30th of a second, the locomotive travels 1.2". Likewise at 1/120th of a second exposure, the locomotive moves only .3" The only way to eliminate motion blur from photographs is to decrease the amount of time the chip spends looking at the object. The only way to do this is to increase the amount of light on the object, so the chip can "see" things more quickly. To some extent, this can be done by increasing the sensitivity of the camera, or increasing the apeture to allow more light through. In the end, though, it's just better to have as much light as humanly possible on the subject being photographed.
