Digital Photography SLR
Understanding Sensor Size

When buying a digital photography SLR camera one of the things you should consider is sensor size. In DSLR cameras there are two sensor sizes, full frame and APS-C. The size of your camera's sensor will affect the pictures you take. Let's look at the difference between the two.

Full Frame

A full frame sensor is the size of a standard 35mm film frame. If you have any experience at all with film photography you can roughly remember the size of one frame on a 35mm roll of film.

Your camera's opening is round like the shape of the lens. When light comes through, it is in a column shape. Here's a crude drawing of a camera lens for you.

This is the shape of the lens and camera opening, but pictures aren't round they are rectangular. In order to make the rectangular picture cameras are fitted with rectangular sensors. A full frame sensor will cover as much of the surface area of the circle a rectangle can cover.

A full frame sensor gives you a truer sense of what you can see with your eye before taking the picture. The larger sensor can hold more megapixels giving you a clearer image.

Cameras with full frame sensors are quite expensive though. If you're not interested in being a professional photographer it isn't necessary to have a digital photography SLR camera with a full frame sensor.

APS-C Sensors

APS-C sensors are more widely found in DSLR cameras. These smaller sensors are cheaper to produce and are found in entry level and mid level cameras.

APS-C sensors cover a smaller surface area of your camera's lens meaning that it captures less of the image entering the camera. Here's an example of what I'm talking about. The brown line represents a full frame sensor and the blue line represents an APS-C sensor.

Crop Factor

When you're working with a camera that has an APS-C lens you have to calculate for crop factor in your photographs. Because an APS-C lens covers a smaller surface area it cuts out the edges of the picture giving the effect of changing the focal length of the lens. This is referred to as a focal length multiplier. To find out the true focal length effect of the lens you're using with your APS-C sensor camera multiply the focal length by the crop factor.

Different camera brands have different crop factors. Here are a few examples.

• 1.3 - Canon EOS-1D Mark IV, 1D Mark III , 1D Mark II
• 1.52 - All Nikon and Sony DSLR cameras except the full-frame models
• 1.53 - Pentax K10D, Pentax K200D
• 1.54 - Pentax K20D, Pentax K-7
• 1.6 - Canon EOS 7D, 500D (T1i), Canon EOS 550D (T2i), 60D, 50D, 1000D, 40D, 400D, 30D, 450D, 20Da, 350D
• 2.0 - Olympus E-400,E-500,E-300,E-1

For example, if you owned a Canon EOS 7D and you used a 28mm lens on the camera the crop factor would be 1.6. This means that if you use that wide angle 28mm lens on a full frame camera it would work as it should as a true wide angle lens, but on your Canon it will work like a 45mm lens (28mm x 1.6).

In certain cases crop factor does have its advantages. If you use a zoom lens you'll get more bang for your buck. This can be an advantage for wildlife and sports photographers.