Understanding Low Light Noise at High ISO

by snapshot2 Moderator - 11/5/08 6:20 PM

In Reply to: (NT) Camera Tips and Information by snapshot2 Moderator

Low Light (without flash) is the Achilles heel of the small digital camera.

To build a small camera you must reduce the size of the lens.
That means you must reduce the size of the CCD sensor.

When you reduce the size of the CCD sensor, you get more noise from the CCD sensor.
Noise is similar to "grain" on 35mm film.
When you use high ISO settings on digital cameras you get noise.
When you use high speed film on 35mm film cameras you get grain.
It looks about the same.

When you put the digital camera in Auto mode (without flash) and use it in a low light situation, the camera will see that it does not have enough light to get a good exposure.
The camera then must raise the ISO setting from its normal 80 to a higher setting.
The Canon SD900 can go as high as ISO 1600.

You will start to see noise at ISO 200 and at ISO 400 it becomes easy to see.
At ISO 800 the noise is intrusive.
At ISO 1600 the noise completely ruins the picture.

To see the ugly side of noise go to this link:

http://www.steves-digicams.com/2006_reviews/sd900_samples.html

Notice the series of photos of the stuffed animals.
They look just about equal at that small size.
But look closer and you see the difference.

Click on the photo that was taken at ISO 80 and you will see a quality photo.
While it is downloading you can scroll around and see the photo at 100% size. Notice the smooth surfaces of the plastics and metals.

Click on the photo that was taken at ISO 1600.
While it is downloading look at the not-so-smooth surfaces of the plastics and metals.
Sharpness and contrast are poor.

.....................

Now for comparison....
Look at photos from a camera with a much larger lens and a much larger sensor.

http://www.steves-digicams.com/2006_reviews/rebelxti_samples.html

Look for the photos of the two bobble-head dolls.
Click on the ISO 1600 photo.
Notice the small amount of noise.


..............

You can take good low light (without flash) photos with the Canon SD900.
You have to gather more light without raising the ISO setting.
Most cameras will let you set the ISO setting at ISO 80.
Now the camera will have to get more light by other means.
The camera will then have to capture the image by using a slower shutter speed.
That means you must put the camera on a tripod to keep it steady for a longer period of time (up to 15 seconds).
You do not want any moving things or people in the shot.

...
..
.