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ISO (ASA)

From: Photography 101

Video: ISO (ASA)

To explain ISO, it might be easier if I step back in time a little bit, and talk about film. For those of you that used to buy film, you'll recall that you had to buy it based off of its speed, called the ISO, or even the ASA. Typical film speeds would be 100, like this one here, or maybe 200, or 400, and those were pretty common speeds you'd buy, like in a grocery store for example. If you went to a specialty store, an actual photography store, you might be able to buy film that was even higher speed, like 800, 1600, or even more than that. So, what do all these numbers mean? Well, if you're shooting in extreme light situations, like full on, outdoor sun, you can shoot at ISO 100.

ISO (ASA)

To explain ISO, it might be easier if I step back in time a little bit, and talk about film. For those of you that used to buy film, you'll recall that you had to buy it based off of its speed, called the ISO, or even the ASA. Typical film speeds would be 100, like this one here, or maybe 200, or 400, and those were pretty common speeds you'd buy, like in a grocery store for example. If you went to a specialty store, an actual photography store, you might be able to buy film that was even higher speed, like 800, 1600, or even more than that. So, what do all these numbers mean? Well, if you're shooting in extreme light situations, like full on, outdoor sun, you can shoot at ISO 100.

ISO 100 is great because that gives you the cleanest shot possible. Very, very like or basically no grain at all. As you get into lower light situations, you needed film that was more sensitive. So if you're shooting indoors for example, you might shoot at iso 400 which is going to give you a more sensitive film, but that film is going to give you a grain. You're going to see some texture in that film that you really don't want in there. If you get into the higher speed films, like 1600 or more, you're going to start to see a lot of grain. But this is also extremely sensitive film, and you can shoot in very, very low light.

Even outdoors at night. So that's where film ISO comes into play. In the world of digital, we no longer have to buy film and decide what ISO to shoot for full 24 or 36 exposures. Now we can set it on the camera we can change it from photo to photo. So now lets take a look at how it affects the world of digital and a DSLR, and what happens when you change the ISO, and how it actually changes the image. First let's see how we actually make the change on a camera like a Canon, a Nikon or a Sony.

You're typically going to find a button that's labeled ISO somewhere on the camera in here. So for example, here on the Canon, if I tap the ISO button and then rotate the finger dial here, you'll see that I can change it to settings like 400, 640 and so on. And this one will go all the way up to 6400, and then into a High mode, which is actually even higher than 6400. On the Nikon camera, it's basically the same. You have to find the ISO button. It might be located on the back. Press and hold that, and then rotate another dial. On this particular model, it's under your thumb.

And as I rotate the thumb dial, you'll see that we're changing the ISO speed on there. On the Sony, it's just a little bit different. On this particular Sony model, when I press the ISO button, since there's no LCD on the top, we need to look at the back of the camera. In here we can see the ISO settings that we can choose from. Many of these cameras, you'll notice, also have an auto setting. Auto ISO means that I don't have to think about it at all. The camera is going to automatically choose the optimal ISO setting for me. And by optimal, what that means, is it's going to choose the lowest number possible, because that's going to give be the best image quality.

Now hold on a second, we're talking about digital. Back in the days of film, we had to worry about the film grain. But in digital, what do we have to worry about? There's no more film grain. Well it turns out, there's something very similar. It's called digital noise. You might also hear that referred to as digital grain. Now what we're seeing in there, is little specks of noise that show up on the image, as we get into the really high ISO settings. Now, modern DSLRs are getting better and better, and giving us an incredibly high quality image, even at the very high ISO settings. Which means that we can shoot in even lower light situations, than ever before possible.

Modern DSLRs can actually shoot in situations where film could never go. And still give you an image that's totally usable. Now for your own shooting, you still want to leave the ISO as low as possible. That might be a 200 or 400 setting. And that's going to give you a nice general set up for pretty much any shot you're likely to take. And still give you a really good image quality. If you do need to go to those higher ISOs though. For example, you're in a really low light situation, and you don't want to use the flash, you can certainly change the ISO on your camera. So let's take a look at a chart and talk a little bit about what the different settings are again, when you'd use them, and then what the results are.

If you're choosing a low setting, like ISO 100, 200, 400. What that generally means is that you have lots of light, for example you're outdoors, or you're using a flash, or you have the camera on a tripod. Cuz if you do have one of these low ISO settings and you're in a low light environment, you can have the same picture taken, but with a longer exposure. In that case you're probably going to want to put the camera on a tripod. And the result of this is going to be an image with very low grain, or very low noise. If we go the other direction to the high ISO we're talking 800, 1200, 1600 or above it generally means that your in a low light situation, you probably don't have a flash and your probably shooting hand held.

The result of this of course is that your going to get visible noise on your image. Again, the best DSLRs are going to give you less and less noise in the image, but you are going to see more noise than you would at a lower ISO setting.

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Photography 101

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Joseph Linaschke
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