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What Is ISO

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ISO is actually a common short name for the International Organisation for Standardization.

The ISO setting on your camera is something that has carried over from film. Remember back in the ‘old days’ when you used to go and buy your rolls of film and you would buy film rated at 100, 200 or 400, maybe even 800 or 1600? Well that number refers to the film’s sensitivity to light. The higher the number, the more sensitive to light the film is. The ISO bit is from the standards for film sensitivity, and the number refers to it’s rating.

So what does sensitivity mean? Well a low sensitivity means that the film has to be exposed to light for a longer period of time than a film with a high sensitivity in order to properly expose the image. With a lower sensitivity you also get a better quality image too which is why you should always try and use the lowest sensitivity you can get away with. Let’s not get ahead of ourselves though, a little more explanation is required.

You might remember buying film for a sunny holiday and the shop assistant would recommend using a film rated at 100 or 200. If, on the other hand, you were going to be taking pictures indoors, then you might be recommended a higher sensitivity like 400 or maybe 800. If you used ISO100 film and decided to take some pictures indoors, chances are you would need to use the flash, or your pictures would come out quite dark.

This is because the film’s sensitivity is so low that the shutter would need to be open for a long time to let enough light in. Your camera may not have had the features to allow it to keep the shutter open for long enough, which is why you ended up with dark pictures.

This was one of the problems with film. Once you’d loaded it into your camera, you were pretty much stuck with that film sensitivity for 24 or 36 shots.

Bring on digital cameras and you can now change the ISO setting for each shot you take. That is one of the big advantages of digital photography.

So why do you only get choices like 100, 200, 400, 800, 1600 and maybe 3200 when it’s digital, surely you could set 154 or 958 if you wanted it? It’s only electrical currents and circuits after all, not a piece of film. Well, in theory you could choose any setting you wanted, but imagine how tricky that would be.

There are three settings which combine to give you the exposure, these are Aperture, Shutter Speed and ISO. Each one can be changed individually to allow you to set then to what you think will give you the perfect exposure, or you can let the camera set them for you to what it thinks is the perfect exposure for the conditions it can detect. Already with three different options, each having several settings themselves, the combinations are numerous, so keeping ISO to set values, which people will understand makes it a little less confusing.

Now, I mentioned quality too, and that better quality images are achieved with a lower ISO number. If, again, you go back to film days you may remember the sort of grainy effect some images had. Well this grain effect is what is introduced with a higher sensitivity film. Digital has it’s own grain effect with higher sensitivity and is known as Noise.

Digital noise can be seen a sort of speckley effect in areas of similar colour, like skies or dark shadow areas. It is a subject of much discussion and the camera is often judged on the amount of noise it produces at these higher sensitivities. This is why you should always try and keep your ISO set to the lowest number, and use aperture and shutter speed to get the right exposure. If you can’t do that with aperture or shutter speed, move up to the next ISO setting and try again.

Why is a high ISO setting needed? Well for indoor work, where flash isn’t allowed and the light levels are fairly low. Or you can use it deliberately to get the grainy gritty feel to the image (although I would prefer to add this later on the computer).

It’s well worth experimenting with ISO settings so you can see just how your camera performs at the various levels. Once you have got to grips with how changing Aperture, Shutter Speed and ISO effect your image, you’ve pretty much got all the technical fundamentals nailed.

Over at the Digital Photography School Blog there is a nice post on how to choose the right ISO setting which is worth checking out.

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Written by bargainmemorycards

February 20, 2009 at 10:38 pm

Shutter Speed

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Shutter speed is a setting on your camera which controls the length of time the shutter is open, allowing light through the lens to the sensor inside your camera. Shutter speeds can go from very small fractions of a second, to several seconds long on most cameras.

So why would you want to change it?

On a very bright day when there is a lot of light, if you allow the shutter to be open for too long then too much light will get to the sensor. When this happens you end up with pictures that are very pale and almost all white. This is known as being Over Exposed.

Let’s say, for a simplified example, that to get a perfectly exposed image on a bright sunny day, ignoring all the other camera settings, that you need the shutter to open for half a second. This half a second allows just the right amount of light through to the sensor to get a well exposed imaged.

Now, as the day goes by and you get to the evening, there isn’t as much light about. So if you took a picture and your shutter speed was still set at half a second you would end up with a very dark image, or an Under Exposed image. This is because not enough light got through to the cameras sensor in that half a second. So in order to compensate against lower levels of light, you would need to keep the shutter open for longer.

This may seem straight forward enough, but the longer the shutter is open, the more chance there is of ending up with a blurred image. The slightest of movements while the shutter is open will register as a blurred effect. Sometimes this can be the desired effect, but most of the time you want a sharp image. Using a tripod, sitting the camera on a solid object like a wall or the floor or holding the camera against a solid object like a big tree or wall can help reduce the chances of getting blurry images.

Most digital cameras will have a fully automatic setting where it decides what settings are best, so all you have to worry about is pointing the camera in the right direction and pressing the button. This may be the mode you use all the time, but it’s well worth experimenting with these settings yourself to see what effect they have. Once you start to understand these settings and what they can do to your image you will open up a whole new range of photographic opportunities and much more creative and pleasing photos.

Written by bargainmemorycards

February 20, 2009 at 10:02 pm

Posted in Photography Tips

Undersatnding Aperture

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Aperture is the term used to describe what is simply the hole in the lens that light travels through to reach the camera’s sensor or film. This hole can be set at different sizes, and combined with shutter speed, you get the two main settings which control exposure.

There is some maths involved to get the actual values, but to be honest, that doesn’t really matter. What’s more important is to know what aperture is, and what happens when you change it. Getting your head round aperture can be a bit of a hurdle, so hopefully this will help a little bit.

The first thing to get your head round is that the smaller the number the larger the hole. OK, that may sound a little odd but in this example f2.8 is the largest hole, and f22 is the smallest hole for the lens shown in the next photo.

aperture

Don’t worry about the ‘f’ either, there aren’t ‘g’ settings or ‘z’ settings, but it’s handy to know that when someone says “I used f8″, you know what they are referring to.

There are of course a range of settings in between the ones shown, and depending on what lens your camera has may effect what settings are available to use, but this should give you an idea of what is actually happening when you change the aperture setting on your camera. By making the hole smaller, you are reducing the amount of light that reaches the sensor or film in the time that the shutter is open. So from this you can start to see how shutter speed and aperture work together.

For example, if you are getting the perfect exposure with a shutter speed of 1 second and an aperture of f8, and then it gets a bit darker. You want to let more light in, so you can either keep the shutter open for longer, or make the hole bigger. Both will let more light in, but both have their own effects on the image, and it is these effects you should learn to understand.

Written by bargainmemorycards

February 20, 2009 at 9:36 pm