ISO

[FramerPDX]

Can someone help out a newbie and explain what the ISO speed does thanks I know this sounds stupid but I am going to practice with my camera all winter long and want to get kind of good with it so any help would be nice thanks ...

your all good photographers...

thanks again...


-Ty

[Dans_D60]

ISO (and previously ASA) refers to the sensitivity of the film (film cameras) or sensitivity of the sensor (digital cameras). For the most part, a larger number means the sensor is more sensitive to light. Less ambient light requires a “higher speed” (larger ISO number) to achieve the desired results. On the other hand, higher ISO numbers also mean more noise (more grain with film). The extra noise makes the image look grainy and of course the noise replaces the actual pixel light and color so “real” data will also be missing. The combination of ISO speed, lens, and light source is photo course in itself. Basically lower ISO numbers will result in images with few noise artifacts and appear “sharper”. Most actions shots require very fast shutter times. Since less light is hitting the sensor with these fast shutter speeds, higher ISO may be needed even in bright light. Here is a good article on ISO for film but the basic theory is the same for digital: http://www.kodak.com/global/en/service/faqs/faq0010.shtml

Dan
http://www.pettusphoto.com

[robertwgross]

What Dan stated is true. I would add only a guideline for a newbie:

Bright sunny day... use ISO 100
Cloudy bright day... use ISO 200
Cloudy gray day... use ISO 400
Indoors normal light ... use ISO 800
Indoors dim light... use ISO 800 or higher

These are only intended to get you started, but you see something easy to remember. Once you get good, then you can make your own list.

---Bob Gross---

[Longwatcher]

Dans_d60 wrote:
On the other hand, higher ISO numbers also mean more noise (more grain with film).

http://www.pettusphoto.com


Technically, there are actually less silver halide grains in the higher ISO film, but they are larger so they change faster when hit by light.

In the case of digital the sensitivity threshold is raised at higher ISO so that the Signal-to-Noise Ratio (SNR) is worse.

In either case raising iSO results in more noise as stated.