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Introduction To ISO

What's ISO, how and when can it be used? We answer these questions here.

| General Photography
Quite a few of our tutorials so far this month have mentioned using the ISO feature on your camera, however if you're new to photography, this feature maybe something you've never used before so here's a brief introduction to what it is and why you'd use it.

Digital cameras use a sensor that converts light to analogue signals, which are then processed in the camera to create a digital image. You can adjust how sensitive the camera's sensor is to the amount of light that's around by changing the ISO. The higher you make the ISO, the higher the sensitivity of the sensor is which means you can still produce images in low-light situations, for example.

Most digital cameras now have a wide sensitivity range that reaches from ISO100 right up to and beyond ISO1600. For example, the Pentax K-3 which is currently featured in a trade-in offer has an ISO range from 100 to 51200.  You can also expand the ISO range of some cameras when needed. 


Increasing the ISO of your camera so you can take images indoors or at night is great but by increasing the ISO your images can be more susceptible to noise, which appears as randomly-spaced, brightly coloured pixels. Having said that, camera companies have made vast improvements when it comes to controlling noise at higher ISO levels but as Robin Whalley suggested in a previous article, it's still worth taking a series of identical shots at various ISO levels to compare how much noise is in them. That way, you'll find what limit your camera has and what level is best to use. You can also check the quality of your shots while out shooting on your camera's screen and reshoot if necessary. Use your camera's magnifying option to zoom in part of the image as it makes it easier to spot noise. Also, it's good to remember that there may be times when it's better to have noise and a sharp photo than no noise and a blurred subject because of camera shake or movement.

In most situations it's best to fix the camera on a lower ISO setting, however there are some situations when a higher ISO is needed.

Introduction To ISO: ISO Noise Test Chart
A shot without noise         The same shot with noise

When To Use a Higher ISO

As mentioned, when working in low light it can be difficult to achieve a quick shutter speed but by increasing your ISO, you'll get the quicker shutter speed you're looking for. At concerts where you can't use flash and won't have a tripod because they're not allowed, slow shutter speeds will result in camera shake spoiling your shots so increasing your ISO to give you a faster shutter speed will mean you can shoot photos of whoever is on the stage hand-held.

It's also a useful tool for when you're photographing a subject such as close ups of flowers in the shade. You may have set the exposure manually using a small aperture to ensure maximum depth of field but the resulting shutter speed is too slow to prevent the wind movement blurring the subject. But by switching to a faster ISO it will help increase the shutter speed to freeze the movement of the flower giving you a still, blur free shot.

When A Little Noise / Grain Works

Grain/noise can add interest and feeling, making portraits more gritty and it gives landscapes a more moody feel, particularly when converted to black and white. Do remember though digital noise isn't the same as grain you get in film and chances you'll have to tweak your digital images slightly to make them more appealing. Another point worth mentioning is that a lot of cameras do now cope quite well at higher ISOs, producing less noise as a result. However, you can shoot images at lower ISOs and add grain to your images in whatever editing software you use.

Pentax Trade-In & Cashback Offers: Purchase a PENTAX K-3 and receive a minimum of £85 when you trade in any camera, plus you can claim up to £85 when you purchase a PENTAX K-50, PENTAX K-5 II or PENTAX K-5 IIs. 


Introduction To ISO: Introduction To ISO:

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altitude50 Avatar
altitude50 19 24.1k United Kingdom
17 Dec 2013 4:18PM
I was taught that the sensitivity of the sensor always stays the same and that the ISO increase is done internally in the electronics. Or have I been taught wrongly?
ChrisV Avatar
ChrisV 17 2.3k 26 United Kingdom
17 Dec 2013 4:30PM
I think the shorthand here is the sensor, plus its processing circuitry = sensor sensitivity. A sensel is a sensel and it collects what it is capable of. Each time you increase the sensitivity by a stop, you're halving the sample rate of the photons that are collected by the sensor - hence doubling its 'sensitivity'.

That's my understanding anyway - it also makes it logical that the ISO stops double in a geometric progression rather than going up in multiples of 100.

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