On Oct 31, 2006, at 6:53 PM, William Robb wrote: >> How does the base ISO in a sensor come about? Is it an intentional >> design component? > > I expect they do it the same way as with film. > I don't recall the formula now, but there is an iso standard that is > pretty repeatable by the common man.
That's measuring/calibrating the ISO sensitivity. Several of my friends work or worked at Agilent where imager development goes on... The sensitivity of a sensor comes from many things, but is ultimately derivative of what the light energy impinging on the chemistry of the photosites produces as electrical potential. A few factors that effect sensitivity, simplistically: - area of the photosite - voltage environment of the photosite array - efficiency of the microlens used on the photosite well - efficiency of the supporting circuitry Designers of imaging sensors typically try to maximize sensitivity while minimizing noise, and there are many physical constants here that limit deviation from a norm to within a very small range of values. From most of my friends at Agilent, what the whole thing boils down to in general is how large the photosite is and how efficient the microlens is at delivering light energy to the photosite well. For example, Canon improved the sensitivity of the 20D over the 10D model, despite decreasing the pixel area, by increasing the size of the microlenses on each pixel well, making them more efficient at gathering light energy. Godfrey -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
