Why bother with digital SLRs?
This post is of interest only to those at my particular intermediate level of knowledge of digital cameras.
Some background: SLR film cameras are generally considered far superior to other designs for professional or serious amateur use. The reason for this is easy to understand: the viewfinder on an SLR camera looks out through the lens so that you see exactly what the film will "see." When you press the shutter, a little mirror pops out to redirect the light onto the film.
Digression: I suddenly realized a few weeks ago that this technology is the reason that, on television, in scenes that involve fashion shoots and such, the camera shutter noise is often accompanied by an instant of blackness. That's what someone using an SLR camera sees at the moment of taking a picture.
Now, that being the case, it was never clear to me what the advantage was of a digital SLR. Since virtually all contemporary consumer digicams have an LCD screen that shows the view through the lens, isn't that an actually superior method to messing about with mirrors and viewfinders?
Digital Cameras - A Basic Beginner's Guide to Digital Camera Technology is the first article I've seen that actually addresses that question:
Small sensors, and the sensors used on all consumer digital cameras, use a scheme which can read the data from the sensor in real time using a scheme called "interline transfer" and the CCD electronics control exposure rather than a mechanical shutter. Large sensors used on more expensive Digital SLRs are often of a different design known as full frame - which doesn't refer to their size, but their design - and which require the use of a mechanical shutter. They don't read out and the display the data in real time, only after the exposure so they can't give real time LCD displays or record video. The advantage of this scheme is that the whole pixel area can be used to capture light while interline transfer CCDs use part of each pixels to store charge. Since smaller pixel areas generate more noise and interline transfer CCDs are not only smaller to start with but use some of their pixel area for charge storage, their noise level is significantly higher. So the smaller interline transfer sensors in consumer digital cameras yield lower quality images than those used in higher end DSLRs, they can do more "tricks" like recording video clips and giving a live image display on their LCD screen. The lack of a mechanical shutter also makes the cameras cheaper and simplifies construction.
And now you know.