The efficiency of a scientific camera like http://www.princetoninstruments.com/products/imcam/proem/ is specified by the quantum efficiency vs wavelength. The meaning is simple enough. Assuming a fill factor of 1, it's the fraction of incident photons that generate a charge. But photographer cameras are specified by some digital-equivalent ISO film speed. For example, this camerahttp://www.usa.canon.com/cusa/about_canon/newsroom?pageKeyCode=pressreldetail&docId=0901e02480fb7db6 [Broken] boasts an equivalent 4000000 ISO. How can I compare the sensitivity of this camera to the above? Is this number useful for anything? Can one simply increase the ISO by increasing the ADC gain (but not actually improving signal to noise)? I have a nagging suspicion that this is just a marketing number which is far removed from actual physical meaning. Of course, the scientific camera doesn't capture color information, which probably can't be done at high efficiencies.