What do the different ISO speeds in digital cameras do?

Question

For example, what is the difference between ISO 200 and 400.

Answer 1

This has been answered, but I'll sum everything up for you.

ISO 400 is twice as sensitive to light as ISO 200.

In a _digital_ camera, just as other people have said, ISO refers to signal gain. Higher ISO means more sensitivity to light.

Your digital camera has 3 different ways to control the amount of light it gets.

1) Shutter speed. The longer you keep the shutter open, the more light gets in. When you're inside or it's at night, you can open the shutter for longer to let in enough light. The problem, though, is the longer you have the shutter open, the more "movement" shows up. If your hands are shaking, the picture will look blurry. If your subject is moving, it will look blurry!

2) Aperture. This controls how big of an opening you use to let the light in. A bigger opening lets in more light, but only a small area of your photograph will be in focus. If you use a smaller aperture, more of your photo will be in focus.

3) ISO. This is light sensitivity. You get "more light" if you turn it up, but it looks grainy. If you can get enough light through other means, keep your ISO low.

The amount of light is measured in "f stops." Each "stop" is twice as much light as the previous one. Sooo, if you turn your ISO up from 200 to 400, you're getting twice as much light. That means you can use a shutter speed that's twice as fast - from 1/30th of a second to 1/60th of a second, for example.

Once you learn how to use all three controls together to get the effect you want, you can make great pictures!

Answer 2

The ISO numbers are a carryover from film photography, where the film was rated for its sensitivity to light. The higher the ISO number, the "faster" (more sensitive to light) the film was. Higher ISO numbers are better for low light situations and for some high shutter speed action shots.

In a digicam, you have only one sensor to record the light, so you cannot switch to a higher ISO sensor. Instead the camera electronically simulates changes in ISO by raising or lowering the signal strength from the sensor.

Thie simulation works reasonably well at lower ISO numbers, but starts to fail at higher ISO numbers, and generates electronic "noise". This looks like little dots, especially across high contrast areas. You get noise when there wasn't enough light gathered to record the correct pixels.

When this happens depends on the quality of the digicam. D-SLR's have the least noise, lower quality compacts the most.

But sometimes having a pic with some noise is better than having no pic. And often there is noise that is visible on a computer screen, but it will not show on a print.

The Automatic setting for ISO seems to work pretty well. If you are shooting in really low light, you may wish to force the camera to use a higher ISO setting.

Good Luck

Answer 3

This is the film speeds of shutter and the lower the film speed the less movement is required. ISO 200 is almost the slowest you can use, tell everybody to hold REAL still or it will turn out blurry. The shutter and image placed on the film run at different speeds. ISO 400 is what most people prefer. Good for personal photographs of landscapes and pictures of people posing for you. ISO 800 can be used indoors without much light and any movement, like a waterfall, river, should turn out. ISO 1000 is what I use, sometimes if it is a once in a lifetime photo I use ISO 1600. Any ISO 1000 can be taken anywhere and in low light conditions, like in your house; or at a BBQ where there are people moving about you won't get photos all that blurry as you would have with a Speed of 200. ISO 200 is film where everybody needs to stand still big time! Not a good film, photos usually don't turn out very well at all. At ISO 1000 you don't need to worry about ANYTHING. ISO 800 is good for all round photos taken inside and outside! I hope this helps. There is also a ISO 600, another good film speed. Usually ISO200 needs a tripod because any movement is caught on film. So, you have a roll of 400 will work for most photos using a flash when needed indoors or at dusk at night. I use ISO 800 because it is universal, ISO 1600 is fantastic, crisp, movement OK. The higher speeds are harder to find because most folks don't know this stuff and end up with blurry photos and are bummed out. So go ISO800, or ISO 1600 for weddings and parties inside. And you can still use it outside at a BBQ and later into the evening that night too!

Answer 4

What is also remarkable is what the newer cameras are able to do with higher ISOs. On my Canon Digital Rebel 350XT for instance, I can use ISO 1600 (very sensitive) with the lens way open (f/1.4) and shoot in candlelight. Witness the pictures I did linked below in the Freedom gallery and at the Isla Vista Juggling Convention. At the IVJC, I was able to use a fast shutter speed to stop the motion with available light using high ISO and wide open shutter.

What makes that possible is the chip in the Canon is very thermally quiet (is uneffected by ambient temperature). The same can be said for the Canon SD700 which is their new point-and-shoot. There you can actually use ISO 800 without a lot of noise. Another thing that helps is digital post-processing software like Noise Ninja or Clear Image that helps get rid of the speckles due strictly from thermal noise.

We are now able to shoot pictures in light that would have been impossible for film. We are handholding cameras in areas that would have taken tripods and seconds long pictures because of the sensitivity of the sensor and image stabilization (gyroscopes built into the camera or lens).

Answer 5

ISO is the sensititvity of your camera to light. However, unlike with film, this sensitivity is emulated somewhat with a digital camera. You get extra light, but it is across the board, not specific to the image. The result is noise as your camera uses higher ISO settings.

So what would you want to use them? There are three things that determine your exposure. The amount the shutter opens. The length of time the shutter remains open and the sensitivity to light.

As you open the shutter more, you lose sharpness to your photo. With the shutter open longer, any movement will show up as smear when you take the picture. In film cameras, you can use higher sensitivity film so you can avoid either of these. In a digital camera, you can up the ISO setting to avoid these but get noise.

More expensive digital cameras have less noise when you do this. Your average $400 camera will have alot of noise. My top of the line $800 Sony DSC-R1 has much less noise. Very high end SLR cameras in the $3000 or more range will have almost no noise.

Answer 6

Everyone is basically right.

Sometimes multiple pixels are used to amplify light, but that lowers resolution.

Also, in FILM the faster (higher ISO) the more grainy the image. Fast films are made by making larger grains of silver salts. This grain equates to noise in a digital camera.

You want to stick with 400 or less ISO for must situations.

If you need fast shutter speeds for low light, up the ISO.

Inside an ISO 100 may use a 1/8th exposure while if you up it to 800 ISO you'll get 1/60th or 1/100th of a second and stop action better, but it may look nosier (color smear and artificats).

Test it out and see what happens!

It's amazing what you learn by testing. I found out there was minimal difference between Fuji's 2 MP and 5 MP settings. Minimal. By dropping resolution you get more pictures, but the 8x10s still look good and you can't see a bit of difference between them in 2 MP or 5 MP.

Answer 7

ISO in digital cameras is signal gain, turn it up and the sensor is more sensitive, but has more noise, turn it down and you need more light to make an exposure but get cleaner less noisy images. ISO 400 is 2x as sensitive as ISO 200.