Content including photographs are Copyright © 2011 - Present - Don & Linda Gilmore
Without getting into the all numbers and scientific jargon, here's a short definition. Remember when you were using film? Not that long ago for some of us. You could buy an ASA 100 up to ASA 400 film. There were also DIN numbers associated with the ASA numbers, basically the same thing. If you used an ASA 100 film it was good for daylight and flash work. If you knew you were going to be shooting in dim light then you'd get ASA 400 film. You were then stuck with what you had in the camera. Not with digital. With the lower ISO/ASA/DIN numbers you will get these results -- photos with less grain/noise but it requires more exposure to light, wider apertures (i.e. f.2) or longer shutter speeds. With higher ISO/ASA/DIN numbers you will get these results --- photos with more grain/noise but you were able to use smaller apertures (i.e. f8) or shorter shutter speeds.
In the case of film with the lower ASA numbers or "slow film" you got a smoother grain in the film -- thus more detail. With higher ASA numbers or "fast film" you got a course grain in the film -- thus less detail and reduced image quality! With digital it's basically the same. With low ISO settings (less gain in sensitivity) you get a cleaner image with less noise. Higher ISO settings (more gain in sensitivity) you get reduced image quality and have more noise. AND in fact most cameras have a "noise reduction" firmware in the camera that reduces noise at higher ISO settings -- but most of them also smear detail and thus cause loss of detail at higher ISO settings.. You might be better off not using the noise reduction in the camera, but instead find a good Noise Reduction Program for post processing.
ISO in digital cameras is basically a number that tells you how sensitive the sensor in your camera is at that setting. Higher ISO settings for dim environments. Lower ISO settings for daylight shooting. High ISO = more noise, less detail. Low ISO = less noise more detail.
Your camera may differ from these results! Some of the more expensive cameras will produce better results at high ISO settings while some will produce worse results. Cameras with CMOS sensors typically will produce better results than cameras with CCD sensors.
This example was taken with a CCD sensored camera at ISO 1600. In a reduced size like the one to the right, it doesn't look to bad. See the cropped area in the yellow box below.
When you look at a part of the above image at 100%, (it's full native size), as shown here, it becomes apparent that the quality is not good. Noise has completely ruined this image and has greatly reduced detail. If you don't have any other choices available to get the shot then this might pass for a smaller image to display on Facebook, the web, or in an email. For prints or larger resolutions it would be unusable.
So what can you do? Use a tripod or mount the camera on a vehicle hood. Use a lower ISO setting and a longer shutter speed. Use a bigger aperture setting. Look at Aperture Priority on this page. If you're using the automatic settings on your camera then you may not have these options available. Using aperture priority and setting the ISO is a better choice. This scene is rather dark and that will also increase noise levels. Brighter scenes with more light using the same ISO of 1600 won't have as much noise. These are all things you need to consider and experiment with on your camera.
This example was taken with the same camera as the example above. This one was shot at ISO 100. Clearly a big difference. Noise is almost completely absent in this photo.
100% crop of the above image. ISO 100 produces very little noise in this photo. The camera used for both these examples is a Point & Shoot using older technology (firmware) with an older CCD sensor. It still produces nice, clean, images at lower ISO settings. A lot of the more modern P & S cameras will render the same results. If possible always use lower ISO settings for a cleaner more detailed image.
Be aware that if you use Aperture Priority and set the aperture to a wide setting (i.e. f2 or f3.5) then the camera is going to set the shutter speed, something you need to keep an eye on. With a low ISO setting in low light conditions you'll get a longer shutter speed that will probably make it necessary to use a tripod or mount the camera on something solid. Shutter speeds of less than 1/40 sec. or slower will make it necessary to stabilize the camera. Otherwise you'll get camera shake which will cause blur. Setting the camera on a solid object and using the timer in the camera can solve this problem. Anything moving in the photo will also be a blur. We often use this method as do most photographers.
and a test you should try with your camera.
