What Does the ISO Setting on Your Digital Camera Do?
Difference Between Shooting a Picture at ISO 100 and ISO 3200
You need to balance all three settings to let in the right amount of light. Too much light leads to a blindingly bright, over-exposed photo. Too little light leads to a dark, under-exposed photo. To make things more complicated, each of these settings has a unique side effect that can impact the final look of your picture.
So what, specifically, does the the ISO rating do? And what is the side effect of increasing or decreasing the ISO rating?
ISO Rating - Sensitivity to Light
In the days of film cameras, you could use different "speeds" of film. A higher speed film, like an ISO 400 rated film, would be more sensitive to light than a lower speed film, like an ISO 100 rated film. As with fast lenses, this allowed the camera to capture more light and in turn allowed you to turn up the shutter speed.
While digital cameras don't use film, there is a similar mechanism to affect the exposure of your picture - the ISO rating on your camera. Instead of changing film, you change a setting on your camera and this will determine how sensitive your digital camera's sensor is to the light. A low ISO rating (i.e. 100) will be far less sensitive to the light than a high ISO rating (i.e. 1600 or 3200).
Turning the ISO rating up will allow more light in. You can then increase the shutter speed or shrink the aperture while maintaining the proper exposure - the right amount of light coming in.
What About That Side Effect?
Although cranking up the ISO can greatly increase the amount of light your camera captures, it can also bring with it a nasty side effect - "noise." Noise will make your pictures look grainy, pixelated, and generally nasty. You won't always notice this when viewing a thumbnail version of the image, but if you zoom in to a 1:1 ratio or print out a large version of the image, you'll definitely see the noise.
The camera you use (and its image sensor) will determine how high you can turn up the ISO before you reach an unacceptable level of noise. On my Nikon Coolpix P80, the images begin to look grainy at around 400 to 800 ISO. I wouldn't dream of using anything higher than that. On my new Canon Rebel t1i, though, I can crank the ISO up to 3200 and still get usable results. This is one of those situations where more expensive gear really pays off - more expensive cameras will handle noise better and allow you to use higher ISO ratings.
When Should I Crank Up the ISO?
You'll want to turn up the ISO when you're in low light conditions. The specific event/subject that you're shooting will also determine how high you want the ISO rating to be.
Let's say, for example, that you're shooting an event indoors - like a wedding. You might turn the ISO up to a medium setting (400 or 800). This will allow you to capture enough light to use a moderate shutter speed (1/30th or 1/60th of a second). You'll get well-exposed images, no motion blur, and (if you're using a good camera) a minimum amount of noise.
Alternatively, you might be shooting a sporting event at an indoor arena - like an indoor track meet. Lighting in these arenas is atrocious. To make things even more problematic, you'll need a really high shutter speed (1/250th of a second or higher) to freeze the runners as they traverse the track. To achieve the highest possible shutter speed, you'll want to open up the aperture (this is where having a fast lens helps) and turn the ISO rating up as high as you can (this is where having a good camera body helps). For events like these, I usually crank the ISO on my Canon t1i to 3200 and live with the noise.
Or, you might be taking portraits of someone inside a studio. In this case, you have very fine control over the amount of lighting that's present and you don't want any noise in the photos. So keep the ISO low! Adjust your lighting equipment, and you shouldn't have to (or want to) use a high ISO rating for this type of picture.
The ISO rating is the setting that is most dependent on your camera. Each camera will handle noise differently, and each will offer a varying range of ISO ratings. You'll have to test your camera out for yourself to see just how high you can push it before the image becomes useless. But no matter the camera, the basic idea still applies - a higher ISO rating lets in more light, but also creates more noise.
Published by B. Rock
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- Higher ISO ratings let in more light.
- Higher ISO ratings also generate more noise (graininess) in your picture.
- Higher ISO ratings are good for low-lighting events, like indoor sports.
5 Comments
Post a CommentThird comment. I don't think the article makes clear to the novice camera user that most if not all digital cameras today can automatically pick an appropriate ISO setting based upon shutter speed, aperture, flash settings, and available light. The key is to pay attention to the setting that is selected by the camera and decide if it will be appropriate. If not, adjust the available (priority) settings to make it so.
The tail end got chopped on previous comment. The scale changes that were listed were per liter, per milliliter and per micrometer. Measuring the water in a glass to microliter resolution versus liter resolution with the same measurement equipment will obviously result in less 'noise' at the lower resolution.
Basically, with ISA you are picking which graduated cylinder you are going to fill from your tap.
I was glad to see Cory's comment, since I had the same concern about the explanation. I don't think the response quite hits the mark, although it's headed in the right direction. I don't believe the camera is capturing any more light, it is rather being more responsive to the light that is captured. Use of the term Amplification is highly beneficial, and can be explained to the layman as turning up the volume on your radio. The corresponding noise can perhaps also be described in terms of what you hear when tuning in a radio station on the edge of the radio's reception range. The radio is not able to adequately extract the desired signal from the background.
Another analog might be comparing the received light to water flowing from a tap into a glass. If the flow rate is low or the time the glass is held under the tap is short, there won't be much water in the glass. Increasing the ISA would then be equivalent to decreasing the scale used to measure the water - one unit per liter vers
You're correct. When I said that the ISO rating makes your sensor more sensitive to the light, I meant essentially what you state about amplifying the effect of the light.
The statement "Turning the ISO rating up will allow more light in," is poorly worded in retrospect, and it might have been better put as, "Turning the ISO rating up will allow your camera to capture more light." I was merely trying to state the simple affect that ISO will have on exposure - more light - and I simplified a bit too much. Too bad you can't go back and edit articles on AC...
I understood that a digital camera ISO setting didn't let in more light, but rather amplified the effect of the light that came in. The difference is that amplification makes the noise bigger too .vs. allowing more light (signal) to come in.