Saturday, February 21, 2009

ISO, Sensitivity and Noise in Digital Camera.

According to me a good camera is one which can take clear picture in low light without flash. This feature is achieved by ISO settings. Those who are familiar with film photography will know that different films have different ISO ratings. Even though your camera is most likely not film at all, but rather digital, the ISO setting still does has the same function as older film cameras. ISO determines how sensitive the image sensor is to light. A compact camera like Sony Cybershot have ISO settings of 50, 100, 200 and 400, while a digital SLR will often feature incremental settings of 100, 200, 400, 800, 1600 and 3200. Olympus E420 has a range from 100 till 1600. Higher the ISO setting, the more sensitive the sensor is to light which means signal created by light striking the sensor is amplified to greater degree.

Advantage of high ISO setting - avoid camera shake in low lights.

There is a direct correlation between shutter speed and ISO settings. By increasing the ISO settings, the shutter speed increases proportionately, for example, from 1/15 sec at ISO 50, the shutter speed increases to 1/30 sec at ISO 100 and 1/250 sec at ISO 800. At these later speeds, you'll avoid camera shake and can freeze slow movements.

Disadvantage of high ISO settings - causes grainy picture.

Unfortunately, there is a drawback to using high ISO settings as mentioned earlier amplifies electric signals which is applicable for background noise too which is present in camera's circuitry. This distorts the image signal and creates a speckled or noisy image.

Top left picture (Pic 1) is taken with ISO settings set to 100 and shutter speed was adjusted to 1/3 seconds. Top right picture (Pic 2) in right is the magnified version of Pic 1 which shows that the picture is slightly blurry because of hand shake while clicking the camera.
Bottom left picture (Pic 3) is taken with ISO settings set to 1600 and shutter speed was adjusted to 1/50 seconds. Bottom right picture (Pic 4) in right is the magnified version of Pic 3 which shows that the picture is grainy because of background noise. (click on picture to enlarge)

General Rules and tips for ISO Settings:

  • Use an ISO of 100 or 200 when taking photographs outside in sunny conditions.
  • If the sky is overcast or it is evening time, then use an ISO within the range of 400 to 800.
  • Night time or in cases of low light you might need to set your digital camera ISO to 1600.
  • Use Tripod if taking photographs at low ISO settings in overcast / low light conditions.

How to reduce noise from the picture.

  • Use camera which has got larger sensors because larger photosites found on such sensors collect light more effectively and thus don't need as much amplification to capture a poorly lit scene as a small sensor.
  • Now there are lot of photo editors in market (Adobe, Photosuite, Picassa) which helps to remove noise.

Next I will discuss about interesting stuff : Shooting and Composition.

1 comment:

  1. Nice stuff dude... I really want to learn photography. Though I have a good SLR, I dont know how to use many of its wonderful functions. Hopefully, I will learn a lot from this blog. Good work and keep continuing...