Posted by M.Kumar at 24 May , 2009

ISO Overview

In traditional film photography terms ISO indicates sensitivity of a photographic negative film to light. It is measured in numbers i.e. 200, 400, 800, etc. The lower numbers indicate lower sensitivity of the film with finer quality in the pictures.

In Digital Photography terms ISO indicates sensitivity of the image sensor to light. The concept remains the same i.e. lower the number the less sensitive your camera’s sensor is to light along with a finer quality of the pictures taken. Higher numbers like 800, 1000, 3200 are generally used in dark/ nightly conditions to attain faster shutter speeds. Higher ISO results in grainy/ noisy pictures.

Picture ISO1 is an example that I recently shot in one of the indoor gardens in DC. The left picture has been shot with lower ISO of 200 and the right one has been shot with higher ISO of 1600.

The difference is noticeable. Left picture with ISO 200 has a fine quality as compared to the right which was shot with ISO 1600.

ISO Speed & Exposure

ISO speed affects the shutter speed/ aperture combination you can use to obtain correct exposure.

In darker situations you will probably use the on-board or external flash but if that is not allowed then you would need to use a higher ISO. There are basically two ways of handling ISO:

- Set on “ISO Auto” mode, your intelligent digital camera will run some algorithms and automatically select a higher ISO based on the lighting conditions.

- Manually select the next higher ISO and see if the increased sensitivity allows you to obtain a correctly exposed picture. If it does, you can now take a correctly exposed picture.

When you manually choose a specific ISO you’ll notice that it impacts the shutter speed and aperture needed for a well exposed shot. Suppose you raised your ISO up from 100 to 400 you’ll notice that you can shoot at higher shutter speeds and/or smaller apertures.

Choosing ISO

Choosing ISO settings basically depend upon following factors and you should consider these before setting your camera’s ISO:

• Lighting conditions – Is the subject well lit?
• Grain/ Noise – Is the picture so important that noise has no importance?
• Tripod – Should I use a tripod for shooting fine quality with lower ISO?
• Motion – Is the subject in motion or stationary?

If the subject is well lit, I want fine quality, my subject is not in motion and I have a tripod- I will opt for lower ISO (may be 100 or 200).

However if it is dark, the subject is so important that I don’t care about noise/ grain in my picture, I don’t have time to set up my tripod because I want to shoot a moving subject- I might consider increasing the ISO to 400 or 800. This will allow me to shoot at faster speed and still expose the shot well. d still expose the shot well.

Where to choose higher ISO?

• No Flash Zones- Concerts, Art Galleries, Churches, etc. have rules against using a flash and of course being indoors, these places are not well lit.
• Indoor Sports Events – where your subject is moving fast yet you may have limited light available.
• Birthday/ Disco Parties – blowing out the candles in a dark room and flashing the disco floor can give you a nice moody shot which would be ruined by a bright flash. Increasing the ISO can help capture the scene.

Please leave a comment so as to let me know that this post is at least helping some one

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Tags: Camera, Dark, DSLR, Exposure, Grain, ISO, motion, No Flash Zone, Noise, Photographic Film, Photography, Point-and-shoot, Protrait, Stationary, tripod
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