ACC WEBSITE HEADLINES March 2009, Vol. 1, Article 8
Full-frame vs. Sensor Cropped - What's the difference? by Norm Plummer: norm@normplummer.com If you have moved from a 35mm film SLR camera to a digital SLR, you have probably noticed that your pictures have appeared to "zoomed" in as if you are using a longer lens. This is caused by something called the crop factor. This effect varies somewhat from camera manufacturer but it usually translates to the film camera having a field of view approximately 1.5 to 1.6 times larger than the digital camera. This cropping action gives the effect of a zoomed image. On a Canon Rebel XTi, for example, the field of view will only be about 63% of the film camera, effectively turning a 50mm lens into a 80mm lens. This is caused by the size of the sensor inside the digital SLR - it is not large enough to capture the full image. Higher end cameras, for example the Canon EOS 5D, have a different sensor that will capture the full image. From a practical standpoint, what difference does this make? Here is an example of the same subjects taken with a Canon XTi (cropped sensor) and a Canon EOS 5D (full frame) with a 50mm lens.
XTi (cropped) EOS 5D(full frame) EOS 5D (full frame cropped to XTi size)
The wider field of view is readily apparent which gives the illusion of a longer lens. Of course, the picture is not really zoomed because the sensor size does not affect the focal length or the aperture. Only the field of view is smaller as if it was cropped in Photoshop. To demonstrate this principle, the third photos show the 5D full-frame images cropped in IPhoto to match the Xti images. So why should the photographer care (especially since a 5D costs more than twice as much as an XTi)? Obviously, if you need a wider field of vision, full frame is the way to go. What about the quality of the photo? The XTi has about 10.5 megapixels while the 5D has about 21 megapixels. The XTi images shown are about 3888 X 2592 pixels and the cropped EOS 5D images are about 3500 X 2400 pixels – not much difference. What if you used an equivalent lens on the full-frame camera to correspond to the cropped image (in this case, approximately an 80 mm lens)? The image (which needs no cropping) is approximately 5600 X 3700 pixels. If more pixels translate to better quality, there should be a definite advantage to the full-frame camera since it is a “true” vs. apparent zoom. The effect will be similar to optical versus digital zoom. The other issue is the cost of the lens. To achieve a similar field of vision (and zoom), the photographer will have to purchase a longer lens. The cost difference between a 200mm and 300mm lens can be considerable. However, the comparisons above show that you can shoot with the shorter lens and crop to size in post-processing to achieve the same effect. Which to choose? The first consideration is the size of your pocketbook. Full-frame photography is more expensive by a factor of two or three. However, the higher-end camera will give you more features, wider field and higher quality photos. It really boils down to your needs and wants. Hopefully, this will give you some insight into the differences and help you make a more informed decision. |
Arlington Camera Club