Originally posted by rfortson The CCD in a P&S is much different (smaller) than a CCD in a dSLR. It has nothing to do with megapixels. Salty was correct. A CCD has a native ISO range and the 10MP CCDs just have a different range. It's an effect of cramming more pixels onto the same size CCD. The K100D and K10D have the same size CCD - and APS-C sized sensor. Canon dSLRs are slightly different because they use a CMOS sensor and it's slightly smaller (crop factor is 1.6 for Canon vs. 1.5 for everyone else).
Russ,
I'm getting more confused.
My question was not about the difference between compact cameras and the digital SLRs. I originally asked, why does the K100D only go down to ISO 200, while the K10D can go to ISO 100? The answer Salty gave was that it had to do with "resolution." As I said already, if you want to say that different sensors simply have different maximum speeds, I can buy that explanation. But that doesn't seem to be what you're saying. You speak about the K100D and the K10D have the same "size" CCD. If it has "nothing to do with megapixels" (as you say) and it's just a matter of size, then shouldn't the K10D and the K100D have the same ISO range? But you know that they don't and you seem to explain that by pointing out that the K10D crams more megapixels into a sensor the same size. So apparently it DOES have a great deal to do with megapixels after all. But I must say that the number of pixels crammed into the same space doesn't seem to me to make that much difference to the sensitivity of any individual pixel to light. A "beam" of light is spectacularly smaller than any pixel. If it's a matter of how quickly the camera's brain can process that info, then it's not a matter of pixels per square inch on the sensor and more a matter of the speed of the processor in the camera. I could understand that, too. But I do not think you are saying that.
Not trying to be argumentative. I'm just curious about it. It sounds as if I raised a more difficult question than I realized. I've got books here. I will eventually sort it out. THanks,
Will