ISO: Dark Matters

Tushar Kanwar        Print Edition: October 2012

There's a famous saying in photography circles that buying a fancy new DSLR camera doesn't make you a better photographer, it only makes you a new camera owner. More so, if all you do is keep the camera on full Auto mode for all your shots. To truly push yourself and get the most out of your camera, you need to understand the three pillars of photography: shutter speed, aperture and sensitivity. In the first of a three-part series, we look at sensitivity (ISO) and how even a basic mastery of this oft-overlooked control can dramatically improve your photos.

WHY DOES ISO MATTER?
At its most basic, camera ISO is the level of sensitivity of your camera image sensor to available light. When you begin fiddling around with your camera's ISO setting, you'll notice it is measured by numbers along the ISO scale, starting typically at ISO 100 and doubling from this point to the limit of your camera's capabilities: 100, 200, 400, 800, 1600, etc. Now, the lower the ISO number, the less sensitive the sensor is to the light, and so the more the light required for a proper exposure. That extra light usually comes by way of a slower shutter speed which allows more light to fall on the sensor, which means that low ISOs like 100 or 200 are used in bright situations or when you can stabilise the camera on a tripod.

Now, what if you don't have a lot of light but still need a fast shutter speed to capture motion? You can then choose to bump up the sensitivity of the sensor. Remember the rule of thumb: each time you double the ISO (say, from 200 to 400), the camera needs only half as much light for the same exposure. So if you find that a particular shutter speed is not capturing motion fast enough-children playing indoors, for instance-you can shoot with a shutter speed twice as fast if you go from ISO 200 to ISO 400.

IS THERE A DARK SIDE TO ISO?
If this sounds too good to be true, there is a tradeoff-higher ISOs lead to a grainier image or a decrease in quality, referred to as "noise". This make the image look sort of chunky and low-on-detail. Bear in mind, one significant determinant of the amount of digital noise at high ISOs is the size of the sensor and, therefore, the size of individual pixels used on the sensor. Larger pixels result in less noise than smaller ones. Since DSLRs usually pack in larger sensors than average compact cameras, they perform much better-which translates as turning out better images with lesser noise at higher ISOs.

WHAT ISO DO I USE AND WHEN?
If you can afford to, always try and stick to the "base ISO", which is typically the lowest ISO number of the sensor that produces the best image quality without adding noise. For most Nikon and Canon cameras, that's in the range of ISO 100-200. Within this range, your photos will have the best details, and you need not touch that dial to boost ISO if you're shooting in daylight. ISO 200-400 should be chosen for slightly darker conditions, such as a cloudy day, in the shade or brightly lit indoors. The 400-800 range helps in indoor shots without too bright a lighting. This range works really well if you shoot with a flash, giving you a more even exposure without loss of detail.

Ranges higher than 800 are great for dimly lit events such as live performances where flash is not allowed and tripods may not be an option, or if you simply don't want to "blow out" the subject as often happens when you use the flash. Proceed with caution with ISO 1600 and above as just the sheer ability to capture the shot may not be worth the resultant noise. Average DSLR cameras start faltering at ISO 1600-3200, so it's best to experiment at these settings before shooting. In general, most situations that necessitate high ISOs are when you need to shoot fast action in low light, and you've run out of options in terms of shutter speed/aperture.

WHAT IF I DON'T LIKE THE FALLOUT OF HIGH ISO?
You don't have to shoot at higher ISOs- the alternative is to get more light, either artificial or natural, or to select a slower shutter speed and prop the camera on something stable (like a table or a tripod). You could choose a wider aperture (we'll cover these in the coming months). And remember, if you start experimenting with the ISO settings, get into the habit of always checking what ISO you've chosen when you switch on the camera. Many photographers have shot an entire event to find out that they'd forgotten to check what ISO setting they'd used the last time they used their cameras. There's nothing worse than thinking you're shooting at an ISO of 100 only to find you had forgotten to switch it back from 1600.

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