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Full-size Sensor On DSLR Camera Has Advantages

2009-06-14 22:48 | Source
When purchasing a DSLR camera, the question of whether to choose full-size sensor is a frequent question. Simply explained, the sensor is the light-sensitive surface inside the camera body that captures light in order to make a photograph. Most photographers describe the size of a camera's sensor by comparing it to the size of a traditional 35mm negative. The APS-C sensor used in Canon's Digital Rebel cameras (T1i, XSi, XT, XTi, XS) and mid-range models (50D, 40D) is slightly smaller than a 35mm negative and it comes with a crop factor of 1.6 (Note that Nikon cameras crop factor is 1.5 instead). The "full-frame" sensor is the same size as a 35mm negative - this is the sensor sized used in Canon's 5D Mark II and 1Ds Mark III  cameras as well as those from Nikon, the D3X, D3 and D700. The recently announced Sony Alpha DSLR-A900 is also a full-frame DSLR camera. Between the APS-C and Full-frame sensor, there is also this APS-H sensor that is used in the Canon 1D Mark III camera at crop factor of 1.3. Here are the most common crop factor ratios:
  • 1.7x - Sigma SD14, Sigma SD10, Sigma SD9
  • 1.6x - Canon EOS 500D, 50D, 1000D, 40D, 400D, 30D, 450D, 20Da, 350D, 20D, 300D, 10D
  • 1.53x - Pentax K10D, Pentax K200D
  • 1.54x - Pentax K20D
  • 1.5x - all Nikon DSLR cameras (except the full-frame D3, D3x and D700); all Fuji; all Sony (except full frame A900), and all Konica Minolta DSLRs.
  • 1.3x - Canon EOS-1D Mark III, 1D Mark II (and Mark II N)

The size of the sensor inside a camera determines the field of view that will be expressed in each photograph. Most of the lenses used on DSLR camera bodies cast a light circle intended to cover a full frame sensor/35mm negative. Since a cropped sensor is smaller than a 35mm negative, it captures a smaller portion of the area covered by a full-frame sensor. Cropped sensors also have an effect on depth of field - they increase depth. The difference is not overly dramatic when comparing a full-frame sensor to a size such as APS-C or Nikon's DX format (which appears in cameras such as the D5000, D90  and D300). However if you were to compare the depth of field produced by a DSLR to that of a point & shoot camera, the difference would be quite pronounced. While taking a portrait at f/2.8 with a DSLR would give you a nice blurry, out-of-focus background, f/2.8 on a compact digital camera would put much more of the scene in-focus. The sensors in pocket-sized compact digital cameras are but a fraction of the size of those found in DSLRs, therefore differences in depth of field are very noticeable.

Another major advantage of full-frame sensor is the use of wide angle lenses. Given the crop factor of small sensor DSLRs, wide angle lenses lose their characteristic wide angle of view, for example, a 24mm lens on a small sensor camera with a crop factor of 1.5 takes on the optical characteristics of a 36mm lens. When used on full-frame DSLR, the lens will continue to behave like a  24mm lens offering the same angle of view like a 35mm film camera. In addition to wide-angle photography, the larger full-frame sensor allows for larger pixels on the sensor that provide wider dynamic range and lower noise at high ISO levels. As a consequence, full-frame DSLRs may produce better quality images in certain high contrast or low light situations.

Here is a recent Q&A from San Francisco Chronicle answering a reader question on whether he should go with a full-size sensor for the DSLR camera purchase:

"Q: I'm in the market for a DSLR camera, and I can't decide whether to go for one with a full-size sensor. They're about $2,000 more than models with the smaller APS-C/DX sensors. What makes a larger sensor better, and why the big price difference?

A: On a full-size sensor, the individual pixels are larger so they can gather more light. That produces more-detailed photos and better images in low light conditions. Photos taken with a full-size sensor can be blown up larger without losing quality.

Also, full-size sensors take full advantage of 35mm lenses, so you don't have to worry about the "crop factor" inherent with smaller sensors. That's most important for wide-angle shots, because a smaller sensor will reduce the angle of a lens.

So why do full-size cameras cost more? Because they're physically bigger than small-sensor cameras, and the larger sensors themselves cost more to manufacture (although I doubt it's $2,000 more).

There's also another reason. If Nikon and Canon put full-size sensors in their consumer DSLRs - which boast many professional features as it is - they'd cannibalize sales of the more expensive models."

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