View Full Version : why use ISO
28th April 2008, 11:09 AM
This is a real newbie question so I apologies in advance, hoping someone here can help
ISO, as I understand it, this is the camera enhancing the image to make it brighter, so why touch the iso at all why not just do it in Photoshop or light room? Surely big program like that would do a better job?
28th April 2008, 11:32 AM
As far as I am aware the ISO on a digital sensor relates to some electronic requirement in the sensor either increase in gain or power or whatever on High ISO speeds to capture the lower light. (which is the reason why there is also more noise).
I think its a bit like a volume control for the light. (not to technical i hope):wacko::acute:
28th April 2008, 11:41 AM
OK - scenario
I'm in a church doing a wedding - the church is dark.
I'm trying to do the "All Guests" group shot. This makes the group very deep (front to back)
I there for need to keep all the group in focus - so i need a large depth of field. To get this i need to select an aperture of f16 or f22 ish.
With an aperture like that not much light is let in so the camera would require a shutter speed of around 1 to 2 seconds to complete the exposure.
So I move the camera from ISO 200 to ISO 1000 this giving me 3 or 4 stops extra light. This means I can move the shutter speed back to something usable like 1/30th of a second.
Hope this explains. I use the ISO all the time on weddings - often to help drag in a bit of ambient light when inside shooting.
28th April 2008, 12:11 PM
You're thinking along the lines of in-camera digital zooms are you?
By increasing the iso, the sensor electronics (ifaik) actually "becomes" more sensitive, ie the internal circuits actually boosts the light to signals levels before processing/recording.
You cannot increase the pixel brightness as effectively later off camera, not even with raw files I don't think, and infinitely less so with jpg.
28th April 2008, 05:15 PM
Ah ok, I was thinking of the ISO to be kind of like the recover tool in Light room (but done in camera), didnít realize it was effecting sensitivity etc. Thanks for the explanation. Big help :D
28th April 2008, 05:25 PM
Yup, it's similar to using a faster film in the old days!
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