Friday's Photo Tip - What is ISO?

Friday's Photo Tip - What is ISO?







Dory, over at Can't Remember Diddly, left a comment on last week's photo tip, and she stated:

"When your reader used the numbers 200 and 1600, it made me think that they are confusing shutter speed and ISO".

I will have to admit that I was thinking along the ISO lines too with the numbers that were given, so I thought it would make a good topic for this week.

Just what exactly is ISO, you ask?

Well technically, the letters stand for International Organization for Standardization. They are the standards that define the speeds for film.

It uses an arithmetic and a logarithmic scale to make this calculation, and we recognize it as ISO 100, 200, 400, etc.

Not very interesting a topic so far, but it really is a necessary part of understanding your camera.

Think of it like this - a camera is used for capturing light.

How much light is available for it to capture affects many settings in your camera.

In the days of film, it was important to know your lighting conditions before hand,so you could buy the appropriate film speed. With today's digital cameras, that "film speed" or ISO can be flipped back and forth without a problem.

An ISO of 100 is a fairly "slow" film, which means it needs more light to capture an image. A bright sunny day, or a studio filled with flood lights would be great for this less sensitive ISO setting.

An ISO of 1000 or 1600 is a "fast" speed which is more sensitive to light and can pick up lower light levels - a church or a candle light dinner.

Now, there are always pros and cons to everything, and I will give a few of these for the different ISO settings.

In the film days, a photographer's first choice for ISO was always a lower number - 64 or 100 was about as far as one wanted to go.

The lower the number, the sharper and clearer the image, especially if larger sized prints were going to be made.

One would sacrifice sharpness for graininess as the ISO number began to rise. Grainy photos were the norm for high ISO images.

So, now that we use digital cameras and not film, you would think that we no longer have to worry about this graininess any longer.

Digital has introduced us to something else that we have to worry about with ISO.

Once again, the lower the number the better.

Digital Noise is a problem that begins to creep into an image when a higher ISO is used.

Noise is very undesirable - especially if a larger image is going to be printed.

The digital sensors in the cameras tend to "heat up" as they process images, and the higher ISO settings make them work harder - making more heat.

Heat is one of the reasons for the "noise". Longer shutter speeds, hot days, and prolonged use of the camera also create "noise".

In film, the graininess is spread evenly across the entire image.

With digital, the noise appears as splotches or spots or an overall blurriness, sometimes only showing up in certain shadows or colors in the photo.

The larger the sensor in the camera, the better it is able to handle the noise. DSLRs deliver a less noisy image at high ISO settings than the smaller point and shoot cameras.

The texture in the image above contains noise. Due to the lower light levels, I used a higher ISO when taking the photo.