Comments on: Expose Yourself http://tleaves.com/2007/04/02/expose-yourself/ Creativity x Technology Sat, 17 Mar 2012 05:09:58 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: M. Feldman http://tleaves.com/2007/04/02/expose-yourself/comment-page-1/#comment-3857 M. Feldman Tue, 10 Apr 2007 00:42:18 +0000 http://tleaves.com/?p=818#comment-3857 Thanks for the insight and the reference! Thanks for the insight and the reference!

]]> By: psu http://tleaves.com/2007/04/02/expose-yourself/comment-page-1/#comment-3856 psu Mon, 09 Apr 2007 02:45:40 +0000 http://tleaves.com/?p=818#comment-3856 When you shift the ISO, I think two things happen in the camera 1. The analog amplification used in the sensor is cranked up. My understanding is that there are amplifiers between the photo sites and the analog to digital converters in the hardware. Turning up the gain lets you use the entire range of the ADC while collecting less light. 2. Of course, this means that noise and such goes up, so the image processing pipeline must be adjusted to compensate. The JPEG engines have gotten pretty good at this. The end result of pushing the ISO up is that you get to shoot at faster shutter speed (or smaller aperture) for a given amount of light hitting the camera. So in a sense, in a digital camera the ISO value is a third variable that you can shift around to get to the exposure you want. I googled around a bit. This page seems to have a reasonably coherent and accurate description of what is going on as part of a general discussion about noise. http://www.ronbigelow.com/articles/noise-1/noise-1.htm When you shift the ISO, I think two things happen in the camera

1. The analog amplification used in the sensor is cranked up. My understanding is that there are amplifiers between the photo sites and the analog to digital converters in the hardware. Turning up the gain lets you use the entire range of the ADC while collecting less light.

2. Of course, this means that noise and such goes up, so the image processing pipeline must be adjusted to compensate. The JPEG engines have gotten pretty good at this.

The end result of pushing the ISO up is that you get to shoot at faster shutter speed (or smaller aperture) for a given amount of light hitting the camera. So in a sense, in a digital camera the ISO value is a third variable that you can shift around to get to the exposure you want.

I googled around a bit. This page seems to have a reasonably coherent and accurate description of what is going on as part of a general discussion about noise.

http://www.ronbigelow.com/articles/noise-1/noise-1.htm

]]> By: M. Feldman http://tleaves.com/2007/04/02/expose-yourself/comment-page-1/#comment-3855 M. Feldman Mon, 09 Apr 2007 00:56:34 +0000 http://tleaves.com/?p=818#comment-3855 A too am an engineer, so perhaps you can give me some technical insight. For a given scene, when you raise the ISO on a digital camera, are you really just shortening the exposure time on the focal plane array, or are you doing something else? How are ISO speed and 'shutter speed'( I know there is not really a shutter) related? Do you have two variables here to play with or just one? Thanks! A too am an engineer, so perhaps you can give me some technical insight. For a given scene, when you raise the ISO on a digital camera, are you really just shortening the exposure time on the focal plane array, or are you doing something else? How are ISO speed and ‘shutter speed’( I know there is not really a shutter) related? Do you have two variables here to play with or just one?
Thanks!

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