Photography Terms Explained: ISO

Welcome to the second post of my ‘Photography Terms Explained’ series, where I try to explain some of the technical-sounding photography terms so that anyone can understand them – well, that’s the plan, anyway! By the way, the first one I did was all about demystifying focal length, which you may find useful too.

So, what is ISO, then?

Basically, when we talk about ISO, we’re talking about just how sensitive to light your camera is. It really is as simple as that, and it’s easy to remember too: the higher the ISO number, the more sensitive your camera is.

So, if you dial in a low ISO number, such as 100 or 200, your camera will be less-sensitive to light than if you dial in a high ISO, such as 3200 or 6400.

ISO and Image Quality

So far, so simple. However, it’s not really enough to just know that a higher number means more sensitivity, as we need to know what the trade-offs are when we make our cameras more sensitive to light, and why we would choose to do so in the first place, too.

The first thing to know is that when we raise the ISO, the image quality of our photos degrades somewhat – and they degrade more the higher the ISO we choose. This degradation appears as ‘digital noise’ – dirty pixels that we don’t want to see. However, before you run away and say ‘Well, I’m always going to shoot at a low ISO, then’, take into account that modern DSLRs handle high ISOs incredibly well, with a lot of cameras being able to shoot virtually noise-free at such high ISOs as 1600 or 3200.

Also, the other really important thing to bear in mind is that noise is only ever really apparent when you’re viewing your photos at 100%, or are printing them out at prints of around A4 size or larger. PTR told us for photos that you’ll be sharing on the web, or printing out at 6 x 4, then you just won’t see any noise anyway. So, my advice is to not worry about high ISO and image-quality: it’s always better to actually ‘get the shot’ than not taking the photo at all because you were scared about a little noise…

Which brings me on nicely to…

Why Do I Need to Think About ISO?

And the simple answer to this is because when we make our cameras more sensitive to light by raising the ISO, then we can start to take photos in lowlight without using a flash (click that link for a guide I did earlier on just how to do that), and we can also get faster shutter speeds, which in turn means sharper photos and action-freezing photography.

The logic for this is easy: if we’re in a lowlight situation, such as indoors, then we need to make our cameras more sensitive to the light around us. By dialling in a high ISO, such as ISO 3200, we’re telling our camera that it needs to up its sensitivity, because there isn’t much available light. If we don’t do this – if we just keep our ISO at 100 or 200 – then your photo may end up being completely dark, or, depending on what camera-mode you’re shooting in, your camera may decide to hold the shutter open for a whole second or even longer – resulting in a total blur of a photograph.

But if we have a high ISO, then your camera is nice and sensitive, so it can capture lowlight scenes, and it will also be able to capture these scenes using a fast shutter speed – resulting in sharp photos, even inside, without any flash.

Take, for example, the below photo I took of a band – the high ISO 3200 meant that, even in such dark surroundings, the resulting photo was well-exposed and sharp:

Takeaways and Tips

My personal advice is to really start to use ISO to your advantage – turn off the auto-ISO on your camera, and start to adjust it yourself. Auto-ISO is OK, but it can unnecessarily raise the ISO of a shot when you don’t need it to, and it can also not raise the ISO when you really need it too! So, the best bet is to try it out for yourself – it really is simple.

Keep your ISO low when your outside on a nice sunny day – such as ISO 100 or 200 – for the best possible image quality, and when you’re inside or in really dark conditions, up the ISO to 800, 1600 or 3200. Don’t worry about the image quality degrading, as you just won’t notice it if you view your images at web-size, or print 6″ x 7″ photos – it’s always better to take the photo rather than missing the moment forever.

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