>> as has >> been pointed out many times there are perhaps 40,000 photons available >> to be counted >> > > Wouldn't the number of photons vary considerably with exposure time > (shutter speed)? > It's also a question of the number of electrons available. When a photon hits the sensor, its energy will be used to move an electron from one place to another, thus building up a charge (in an ideal senor - I think a practical one will sometimes require more than one photon.) There is, however, a limit to the number of electrons that may "jump" and/or be held as a charge (no, not "held in charge"...). This limit is believed to be approximately 40000 per pixel or photosite for the 10MP sensor. So while there may be more photons around under good light or in a long exposure, 40000 is the maximum number that can actually be counted.
- Toralf -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
