Sensor Size

Why therefore do camera manufacturers not use the bigger image sensors in consumer digital cameras? A bigger image sensor means the need for a bigger lens. Unlike film that can capture light incident on it at an angle, an image sensor requires that light falls on it straight on. Bigger lens add costs, need a bigger body, etc. etc. You get the idea. You quickly end up with a camera body the size of a... DSLR. Many consumers simply want small compact cameras.

The biggest image sensor on a prosumer digital camera is 2/3 in. sized at 8.8 x 6.6 mm (though most of them now use an improved 1/1.8 in. type). We wait for the day when an APS-sized image sensor is used in a prosumer model!

The next size down is 1/1.8 in. (sized at 7.2 x 5.3 mm) and is prevalent in most of the 5MP, 6MP and 7MP consumer digital cameras today.

Camera manufacturers have 'squeezed' more megapixels into the same 1/1.8 in. image sensor. That is one reason some people say that a digital camera at a lower megapixels resolution gives images that are more noise-free than one at a higher megapixels resolution -- on the same size image sensor. More megapixels on the same sized image sensor means the pixels are closer together -- thus more noise. Of course, better in-camera noise reduction algorithms in the newer digital cameras can counter this tendency toward more noise to a certain extent. Photographers must balance the advantage of higher megapixels versus more noise (albeit reduced with the in-camera noise reduction algorithms), although camera manufacturers leave us with few choices as they all move to the higher megapixels image sensor to compete with one another.

The DSLRs have image sensors that are much larger than 2/3 in. Some DSLRs have an APS-sized (or, 'half-frame', approx. 23.7 x 15.6 mm) image sensor.

When we talk about a 'full-frame' image sensor, it is in relation to a 35mm film and is therefore sized at 36 x 24 mm. Compare these with the 2/3 in. image sensors in prosumer digital cameras sized at 8.8 x 6.6 mm, and you'd agree that the size difference is indeed substantial. No wonder dSLRs produce practically noise-free images.

Are we ever going to see bigger image sensors in prosumer digital cameras? Bigger sensors mean bigger lenses mean more expensive cameras. So that is why most of the work being done now is focused more on improving the small image sensors and writing better noise reduction algorithms. However, we believe it is inevitable for the APS-sized image sensor to eventually move down to consumer digital cameras, starting with the prosumer models.

What Can You Do?

There are a number of things to remember about noise:

• A higher ISO introduces noise.
• Noise Reduction Software will clean up the noise in some images, and sometimes it's done well enough that you can't really tell the original image had unacceptable noise level in it.
• A slow or long exposure introduces noise.
• If you must have the option of using high ISOs (e.g. to capture fast action in low-light situations), then get a dSLR. Since many amateur photographers purchase 35mm SLR cameras today (especially since they are relatively cheap), I don't see why they should not be able to use a dSLR. as easily. The only roadblock to owning a dSLR. for many today is its high price, though even that is steadily coming down as competition heats up among camera manufacturers. We can now obtain a dSLR. for under $1000, including the lens.

Noise is a fact of life in consumer and prosumer digital cameras, and is going to stay with us for some time longer until camera manufacturers engineer better and small noise-free image sensors. Until then, what can you do to reduce the amount of noise in your digital images?

1. Avoid slow or long exposures.
2. Use lower ISO settings. (For more information on why see text following.)
3. When comparing digital cameras, all things being equal, favor the one with the larger image sensor. For example, Camera A may be 3MP using a 1/2.7 in. image sensor (sized at 5.3 x 4.0 mm), while Camera B may also be 3MP but uses a larger 1/1.8 in. image sensor. Camera B will probably produce images that have less noise than Camera A.
4. Purchase a noise reduction software. This will allow you to take pictures and not miss some great shots. You'll find that a good noise reduction software usually does a pretty good job of 'cleaning' up the noise to an acceptable level in most of your noisy images.

This illustration shows the approximate sizes of the most popular image sensors: