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What is ISO?
ISO is of the camera sensor’s sensitivity to light. A sensor with lower sensitivity (lower ISO) requires a longer exposure while a sensor with higher sensitivity (higher ISO) can shoot the same scene with the same exposure at a shorter exposure. Unlike film cameras whose ISO depends on the type of film used, digital cameras have the ability to change the sensitivity of the sensor at any time.

Where is it indicated?
The ISO is usually indicated on LCD screen of your digital camera. It would be clearly labeled with the word “ISO”. As for DSLRs with a status screen on the top, it would not be so obvious, but it is represented by numbers that go from 100 - 3200 (depending on the camera model).

Higher or lower ISO?
A higher ISO would mean that you could shoot a scene exactly as you would at lower ISO but with a shorter exposure. This in turn allows you to freeze the motion of moving objects or prevent the effects of camera shake even when shooting in poor lighting conditions.

A scene during the Lantern Festival at ISO 1600

High ISO?
If shooting at a high ISO has advantage over shooting at a lower ISO, why even bother shooting at a lower ISO in the first place? Yes, we can freeze the motion of moving objects or prevent the effects of camera shake. However, everything good comes with a price. Shooting at higher ISO would generate more “noise” in your pictures. It is however only clearly visible when viewed at certain zoom levels or print sizes depending on your camera (image processor and noise reduction capabilities). For instance, we observe the same shot as above at a 100% crop. Noise is clearly visible.

100% crop of the scene during the Lantern Festival at ISO 1600

Yet another question comes into mind. If noise is only clearly visible at certain zoom levels or print sizes, why even bother about the ISO? The answer to that question is not a simple one. As for me, I would remind myself, why compromise the image quality when I can improve its quality by reducing the ISO and obtain the same results? The key point here is balance. Of course when it is a once in a life time picture moment, use a higher ISO when taking in poorly lit conditions. At least you would have a sharp/crisp picture rather than a blur picture.

An important moment ruined as I refused to use high ISO for this shot

Low ISO?
Shooting at relatively low ISO is also possible in a poorly lit environment provided that you have lenses have a wide aperture (about f/2.0) without compromising the shutter speed (exposure time). However we would only observe shooting at low ISO in a well lit environment (daylight) in this tutorial. Shooting at low ISO would mean minimal noise appearing in your pictures even at 100% crop. As mentioned above, noise is only visible at certain zoom levels and print sizes when shooting at a high ISO. Question now is why would we ever zoom into a picture in so much ? Well, think about group shots. We would want to zoom into everyone’s faces wouldn’t we? Now increase the number of people in the group by ten folds. How much would you zoom in to clearly distinguish whose face belongs to who?

100% crop of Andrew’s face at ISO 100

100% crop of the INTI scholarship recipients at ISO 100

Noise reduction technologies?
In this era, the development of new technology is rapid. Improvements in camera technology have been abundant too. Now, even shooting at high ISO would not create as much noise as it would compared to back then. Just look at Nikon’s D3 and D300. Even shooting at ISO 6400 is sweet. Do look out for Canon’s 5D Mark II which promises of ISO up to 25600. Note that Nikon’s D3 also offers an ISO range of up to 25600. With such interesting developments underway, I wouldn’t be surprised if one day cameras would be able to take pictures in almost total darkness. Bottom line is, if you’re rich and ready to spend, go for better cameras and you could enjoy the higher ISO without the thought of having distinct noise in your pictures!

Conclusion
Consider whether the picture you are taking is once in a life time or an important shot. You should be able to decide whether to use high or low ISO then. Remember, keep shooting!

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