[Lawngnomez]

Can anyone tell me what ISO is and what it does? My camera seems to take better pictures with a really high ISO.

[eneith]

ISO is the number indicating a digital camera sensors sensitivity to light. The higher the sensitivity, the less light is needed to make an exposure.

Digital cameras automatically select the ISO but most have a setting to change it manually. Auto ISO generally works best for bright scenes.

Shooting at a lower ISO number requires more light than shooting at a higher number. Lower numbers result in images with the least visible noise, which is desirable.

The higher the number, the more noise. The amount and degree of noise varies from camera to camera.

Digital single reflex cameras (dSLR), because they have larger sensors, are best for producing noise-free images. However, some consumer digital cameras now have improved sensors that produce acceptable images at higher ISO.

AUTO ISO - digital camera automatically sets the ISO speed according the brightness of the scene, increasing or decreasing the sensitivity. User has no control over which ISO number is used.

ISO 50 - 80 - for taking photos in bright light; excellent for close-ups, landscape, and portraits. Produces fine detail and image quality.

ISO 100 - for extra sensitivity with little, if any, reduced image quality.

ISO 200 - cloudy and overcast days. Acceptable image quality, with some visible noise.

ISO 400 and above - suitable for indoor photography whether a flash is used. Useful for "stop-action" and sports photographs. Most compact digital cameras produce high to very high image noise.

Changing ISO also changes the aperture and shutter speed.

[Milo Dolezal]

ISO = International Standard Organization
ASA = American Standard Association

Both are the same thing - but with different value. For example: ISO 27 = ASA 400.
In this case ISO/ASA assigns sensitivity value to photographic film.

ASA is used in USA and Canada, ISO in rest of the word.

[lschoeggl]

ISO = International Standard Organization
ASA = American Standard Association

Both are the same thing - but with different value. For example: ISO 27 = ASA 400.
In this case ISO/ASA assigns sensitivity value to photographic film.

ASA is used in USA and Canada, ISO in rest of the word.

Cameras in the US most commonly use ISO ratings as well.

[Milo Dolezal]

Cameras in the US most commonly use ISO ratings as well.

I must disagree with you. ASA is the most common film sensitivity setting in the US.

[lschoeggl]

Hi Milo. You may be thinking in terms of film, but because Lawngnomez mentioned that his/her "camera" takes better photos at high ISOs (not that it takes better photos with high ISO film), it sounds to me like this is a digital camera in question. I have yet to see a digital camera that discusses ISO in terms of ASA, so in that respect I think ISO has become universal. However, since ISO and ASA both address sensitivity to light and relative grain levels, I think we've successfully answered Lawngnomez's question and I'm happy to agree to disagree!

[Milo Dolezal]

Yes, indeed, I was thinking "film". ( I am "old school" :D ) Thank you for noticing...

[Digipix]

I think you've got some fairly good explanations here. In a nutshell ISO is light sensitivity. The higher the number the more sensitive. The lower the number the less sensitive. This relates to digital and traditional film.