>> It's been mentioned about two point six zillion times by now that you >> probably don't, though. The sensor itself doesn't have a lot more than >> 12-bits worth of latitude, so producing more bits in the A/D doesn't >> help a lot. >> > > I disagree with that a little. It's still the same sensor reveiving the > photons no matter if you set the ISO to 100 or 1600 in a normal > DSLR. When setting the camera to ISO 1600 you just capture a lot > less photons in one pixel well than you would if you set ISO 100 > (having the same amount of light available on both exposures). This > is because you will have less light entering the sensor to get the > correct exposure. Every single photon generates one electon (not > exactly but to about 70% success rate) and there is a lot of > space for those electrons. A good modern CCD sensor does have 14-16 bits > worth of depth (or latitude). Don't know about these DSLR camera > sensors though, maybe they are just 12 bits :(. I think the actual sensors do have the 14-16 bits you mention - which literally means that the max charge is up to some 65000 electrons. However, they also have a readout noise of at least 10 electrons, which is equivalent to 3 or 4 bits. This essentially means that you are left with a usable dynamic range or latitude equivalent to 12 bits; any additional bits would just be "measuring the noise", if they contained any information at all. That's why a 12-bit A/D is traditionally used.
Furthermore, when you amplify the signal for a higher ISO setting, you also amplify the noise, thus shifting up the 3 or 4 bits so that contain noise, so it enters even the 12 bits you keep. But like I said, this has been discussed a lot in the past few weeks. In in several rounds before that, too. Enough for now. I'm not sure I've read the data sheets of the *exact* sensors used in the Pentax cameras, either, by the way (I've seen technical data for various ones of similar type...) - Toralf -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
