mklotz said:
It's not clear to me how the sensitivity increase is accomplished in a digital camera (photo experts feel free to chime in here) but, increasing the ISO value your camera is using will allow you to take pictures in low light conditions without flash. Higher ISO values will also increase noise sensitivity but Canon does a good job of managing this in their cameras.
I'm no expert, just an avid enthusiast. I stand (or sit) to be corrected, but I think this is how it works.
The little device, either a CCD (Charge Coupled Device) or CMOS (Complimentary Metal Oxide Silicon) chip is what converts the light into a digital output onto your memory card.
The CCD or CMOS has literally millions of photo-detectors (pixels)or sites that will convert light into a voltage, the brighter the light the greater the voltage. ( when I say greater voltage, I'm talking about milivolts)
When you select the lowest or standard ISO (sensitivity) you are using the minimum amplification from the CCD or CMOS chip and thus giving you the best picture quality that your camera can give.
However, if you are wanting to take pictures in darker conditions you can on most camera's increase the ISO (sensitivity) and that then amplifies the output of the CCD or CMOS sensor to produce the same output as when you have normal light conditions.
So why not use higher sensitivities all the time and be able to take pictures in the dark? Unfortunately when you use the higher sensitivities ( ISO's ) you also amplify digital noise that is present in the CCD or CMOS chip. Normally the noise is so low as to not be noticed, but when amplified using higher ISO's it becomes visable especially in shadowy or dark areas of the picture.
I hope this is understandable.
Tim
