ISO is the abbreviation for International Standards Organization. Back in the day before digital when everyone had to use film, manufacturers such as Kodak made films with different light sensitivities. The more light sensitive it was, the film was considered "faster". In order to properly evaluate film sensitivities between manufacturers, ISO developed standards for measuring the light sensitivity of films. This measurement is called the film "speed" and the numbers usually ranged from 32 to 1200 and maybe even higher. The higher the speed of a film, the more light sensitive it is. In order to photograph an indoor scene with existing lighting, film speeds of ISO 400 or higher were used. A common film speed of ISO 100 was often used for outdoor photography.
Digital cameras today have an ISO setting which approximately duplicate the ISO settings of film. In a digital camera, the ISO setting refers to the sensitivity of the camera's sensor that captures the images. You can set your camera's ISO speed manually or let your camera set it automatically for you. In order to get the best quality digital photos, I recommend that your camera's ISO speed be set at 100 unless you are shooting in a low light situation without a flash.
Why not just set ISO at a high number all the time?
There is no such thing as a free lunch! There are trade-offs in using higher ISO speeds even in digital cameras.
Advantages of higher ISO speeds:
- Capture images in low light settings without the need for a flash or addtional lighting.
- "Freeze" rapidly moving people or objects
- Additional "noise" or for films, "grain" is added to the image.
- Possible shift in colors.
Here are several photos of the same objects taken with different lighting and ISO speeds.
This one was taken at ISO 3200:
When this picture is enlarged (click on it to enlarge it), it is possible to see lots of noise especially in areas where there are areas of the same color.
It is possible to remove the noise either in some cameras before the image is written to the memory card. Look for a menu setting of "Noise Reduction".
There is one thing you can do if you wish to use ISO 100 here. Reduce the ISO to 100 and use a slower shutter speed. Here is a photo taken using ISO 100:
This photo was taken using a shutter speed of 1/13 of a second. This shutter speed is way too low to take just holding the camera. I had to put my camera on a tripod to take this.
Another alternative is to set the ISO just high enough to hand-hold the camera. Here is a photo taken at ISO 800 with post-processing noise reduction applied:
"Post-Processing" means that work needed to be done on the computer with this image after the photo was taken and uploaded to the computer. Post-processing is done by a software application such as Adobe Photoshop or Adobe Photoshop Elements. It is very hard to tell the difference between this photo and the one taken at ISO 100. Of course, the difference is the amount of time spent doing the post-processing. Again, there is no such thing as a "free lunch"!
Can you see any difference just looking at these on the screen? (Double click on each photo to view them in their actual size.) However, if these were printed 8x10 or larger, the difference would be very noticeable.
Finally, let's jump into our time machine and go back about 15 years or so before digital cameras. Using a film camera inside without flash, we would use a very fast color film, something like Kodak Max 400, which was a very popular high-speed (ISO 400) film. Here is what the photo above would look like if we were using a fast color film:
Notice that not only is the film grain very visible even at a small size, but the colors are slightly different and in several areas quite blotchy. Since there were no digital cameras back in those days, this was the best one could get at that time. No wonder why there are so few film cameras still in use today! However, some people may like this photo because the film grain makes it more "realistic". You be the judge!
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