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Why small sensor size may leave your photos feeling inadequate

When buying a digital camera, there are many important specs to consider besides which color to pick. In years past, the way you’d approach this was to get the camera with the highest resolution – measured in megapixels – you can afford. But, with many new compact point-and-shoots boasting the same resolution as their higher-end cousins, could they really perform at the same level?

The answer, of course, is no. The 16-megapixel resolution in Canon’s entry-level PowerShot A4000 IS doesn’t mean it’s stronger than Canon’s top-end PowerShot G1 X with a 14.3-megapixel resolution. There are many things that differentiate low-end from high-end, and one you should focus on is the sensor. A camera’s sensor is a highly sophisticated piece of component that captures light through small pixels (also called photosites) and turns them into a digital signal. (How they work is far more complex than our general description, but we know you have better things to do than sit down for a science lesson.) While a compact point-and-shoot sensor may have the same number of megapixels as that of a compact DSLR, they aren’t equal – it’s how big those pixels themselves are.

While resolution is still important, your buying decision should include factoring in the camera sensor. Here are some things to keep in mind.

CCD versus CMOS: Equal but not the same

CCD sensor (left) and CMOS sensor (right). (Images via Wikipedia Creative Commons)

Whether it’s a DSLR or point-and-shoot, digital cameras use one of two sensor types: charged-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS). Without getting too technical, a CCD sensor delivers higher image quality, but is more expensive to produce and requires a lot of power. A CMOS sensor uses less energy and is cheaper to produce, but traditionally it’s larger in size, isn’t as light sensitive, and more susceptible to noise than CCD. A new variant of CMOS, called back-illuminated CMOS, is starting to appear in more and more digicams. Instead of being placed on the front, the wiring that delivers the signal from each pixel in a back-illuminated CMOS sensor is on the back, which allows more light to reach each pixel.

But picking one or the other is unimportant. Thanks to advancements in sensor design, today’s CCD and CMOS sensors are able to produce high-quality images, so don’t get hung-up on sensor type. (The trend in the camera industry, however, is moving toward CMOS.) You should be concerned about sensor size, which we’ll describe next.

Sensor size, not megapixels, is what matters

Compare the size of a DSLR to a pocket camera or smartphone – the difference is noticeable. From this you can conclude that the larger DSLR will accommodate a larger sensor, and in turn a larger sensor will produce the better picture. This is why resolution doesn’t matter solely, because a more advanced camera with a large sensor will trump the low-end point-and-shoot with a small sensor, even if both sport the same number of megapixels. With a small sensor, the pixels can’t capture as much light, so a pocket camera will produce images that have less dynamic range and never as clean as a DSLR. A camera with a larger sensor will also produce images with less noise, especially at high ISO. Of course, the tradeoff in image quality means more convenience.

Manufacturers list sensor sizes for DSLR and point-and-shoots differently. DSLR sensors are measured in width and height in millimeters, but point-and-shoot sensors are measured diagonally in fractions of an inch. For example, Nikon lists the sensor size of its Coolpix S3200 as 1/2.3 inches, while Sony lists its a99 DSLR’s sensor as 35.8 x 23.9mm. To compare the sensor size equally, you can convert either measurement into an approximate measurement in diagonal inches. In the two models mentioned, the Nikon sensor is approximately 0.43 inches and the Sony’s is 1.69 inches. As you can see, the Sony’s sensor is nearly 4x the size, which will produce image quality that’s much better. Sensor-Size offers a handy calculator that does the conversion for you. The site also lists the specs of some of the most popular models.

In the interchangeable lens category, which includes DSLRs and mirrorless/Compact System Cameras (CSC), sensor sizes are also described as full-format, APS-C or APS-H, Four Thirds, and Micro Four Thirds.

A full-format sensor (24 x 36mm) is equivalent to a frame of 35mm film in size, and these sensors are very large and expensive. They are found in flagship DSLR models – you can’t miss them, they look huge and are heavy to carry. These are what many pros use to capture amazing images.

Most other DSLRs use an APS, or Advanced Photo System, sensor. The APS designation is equivalent to the size of APS film formats (14 x 21mm to 16 x 24mm for APS-C and 28.7 x 19.1mm for APS-H). The smaller sensor size of APS-C allows manufacturers to create compact DSLRs that aren’t as powerful as full-frame models, yet still deliver a great picture quality nonetheless.

Another standard, Four Thirds, features a sensor that’s even smaller (13 x 17.3mm). Developed by Kodak and Olympus, DSLR cameras using Four Thirds were made primarily by Olympus and Panasonic. The smaller sensor means a smaller and lighter camera body that can achieve deeper depth-of-field. Four Thirds cameras use a 4:3 aspect ratio instead of the 3:2 of APS.

A new standard, Micro Four Thirds, has the same sensor size and qualities of Four Thirds. Created by Olympus and Panasonic, Micro Four Thirds cameras don’t use a mirror like a traditional SLR, and are far smaller and lighter. However, Micro Four Thirds cameras tend to have slower autofocusing and image quality isn’t as strong.

What sensor do you need?

For online sharing purposes, like e-mail or posting to a social networking site, small sensors in compact point-and-shoots and smartphones will do the job. But if you intend to use your photos for other purposes – whether it’s printing on paper, cropping an image, or publishing it in a magazine – know that cameras with small sensors may not deliver the image quality you’re looking for.

As we noted in our article on how to print large images the right way, resolution (megapixels) play a role in how large an image you can print (check out the article to find out how to determine the print size a particular resolution will yield). However, resolution, as we’ve already mentioned, doesn’t necessarily mean great image quality. If you plan to use your images for commercial purposes, invest in a full-frame or a high-end APS DSLR. For printing at home to share or display, check out entry-level DSLRs, CSCs, or high-end point-and-shoots that feature a large CMOS or CCD sensor.

Remember, although the sensor is more important than megapixels, know that there are other digital camera components – the lens, for example – that are also important.