> > Joe - Thank you for your easy-to-understand explanation. I have been so > confused about this and have tried to understand it. In finally makes > sense. It's about equal to what a digital zoom does on some of the cameras. > It essentially is zooming in on the center of the image and is making that > part of the image and enlarging it so it will fill the whole frame (thus a > not-so sharp image).
You (and Joe) both miss one important point. That 6.1mp sensor in the *ist-D will produce a better digital image than you would get by taking the central portion of an image shot on a 6mp full-frame digital camera such as the Contax (or the 'MZ-D' we saw from Pentax eighteen months ago). That enlarged image would be the equivalent of the digital zoom prevalent on consumer digitals. The limiting factor in digital images, at present, remains total pixel count. To get a cropped image from a full-frame sensor equivalent to that from the smaller sensor in the *ist-D would require a sensor with double the pixels. So not only would you have to pay the significantly higher price of a full-frame sensor, you'd have to pay for a 12mp camera, too. To give you some idea; the Canon EOS-10D costs around $1,500 - the 1Ds costs five times as much. In other words; the alternative to this focal-length multiplier is only 'free' if you've paid five times as much for your camera. The focal-length multiplier is a side effect of the fact that the sweet spot for sensor size, at present, is around the size of an APS frame. Any larger and the sensor becomes very expensive to manufacture; much smaller and the image quality deteriorates because either the individual pixels are too small, and their signal-to-noise ratio goes down, or there are less pixels overall. It's not a true freebie, even then; the cost comes if you want to use wide angle lenses. To get the effect of a 20mm lens on a full-frame image means you'll need a 14mm ultrawide - not a cheap proposition.
