THis might help....
SO (I.S.O.) is the abbreviation for the
International Organization of Standardization, a governing body based in Europe that provides the standards for a wide variety of subjects.For photographers the key standard is
Film Speed ratings. In the past this was known as
ASA or the American Standards Association (Now discontinued and replaced by the American National Standards Institute or
ANSI), and you could buy your films in ASA 50, 100, 200, 400, 800 and 1600. There were specialist films that would go higher or use infra-red although these were generally known as the standard speeds.Most decent cameras now have interchangeable ISO settings which is especially useful for digital photography because, as discussed in the previous chapter, you can change the ISO setting for every shot you take without the need to change film.So what ARE the settings and how do they affect your photos?The standard I.S.O that most people use everyday, giving accurate colour rendition and "clean" noise-free images is 100 I.S.O.If your camera is able to set a lower ISO of 50 or less, you will notice that the images become a little more saturated in their colours. You won't see
too much difference in quality like you do with 50 I.S.O. Slide film, but a slow film speed or I.S.O. with digital photography has its benefits nonetheless.
50 I.S.O or lessThere have been occasions when I have come across a particularly bright scene such as a sunny, white sandy beach or a sun kissed bleach-white property on a sunny day where I simply have too much light all around me.I am already on the fastest shutter speed that the camera will allow and the smallest aperture that I wish to use (N.B. I never try to go smaller than F16 or F22 otherwise the image quality can start to deteriorate, or I may wish to create some depth of field with an aperture of say F5.6). By reducing the I.S.O. to the lowest, I can maybe save a few shots whilst enhancing the colours.Also when shooting images that I want to be rich in colour such as a beach scene with blue skies and deep blue water for a holiday magazine, I use the lowest ISO possible (normally 50) coupled with a
polarizer filter.You may also want to purposely slow down the shutter speed for some creative shots. If you read enough photography magazines you will have undoubtedly seen images of waterfalls with milky smooth water and pin sharp rocks and foliage?The milky water is created by a very slow shutter speed (normally a matter of seconds), which can sometimes only be achieved with the help of the smallest aperture and lowest ISO setting (note, using a
Neutral Density filter will also allow super long exposures during the day to get the milky water effect as in two of the shots of the sea on
this page).The small aperture and low ISO block most of the light which means you need to compensate with a long shutter speed which in effect causes the flowing water to "blur" itself onto the sensor. Obviously when doing this kind of shot a tripod is essential.
Standard I.S.O - 100As I mentioned earlier, this is the industry standard for most situations and subjects. Whether you shoot weddings, portraits, studio or commercial, 100 I.S.O. will do just fine and create nice, clean colourful images across the board.
High I.S.O - 400 and aboveBeing quite a perfectionist myself, as I think most photographers are, I like to produce the cleanest and noise free images as possible. I also like bold, colourful images.Unfortunately, there are some times when you just
have to use higher I.S.O.'s in order to get the shots you need:
