DSLRs are generally divided into two categories: full frame and crop sensor. The difference between the two lies in the size of their digital sensors that capture light and translate them into pixels. A full frame sensor usually has the same dimensions as the 35mm film format, which has been the standard since the early 20th century. A crop sensor, on the other hand, is smaller than a full frame sensor by a crop factor. For example, Nikon’s DX format sensors have a crop factor of 1.5, meaning the ratio between Nikon’s FX full frame sensor’s diagonal and that of DX’s is 1.5, giving users a much smaller field of view. Other manufacturers like Canon and Olympus also have different crop factors for their crop sensor cameras.
Assuming all other conditions are the same, when shot from the same spot with the same angle, crop sensor camera captures only a portion of the image a full frame camera would get. The two images below illustrate this concept. Notice how the full frame image shows a much larger field of view than the second, crop sensor image:
Now comes the question that most beginner would like to ask: which one should I get? There isn’t really a definitive answer to that question. Surely the full frame cameras seem capable of capturing more, and most, if not all, photographers would eventually upgrade to the full frames as they become more professionally developed, but does that extra field of view really worth it?
Take a moment to think about what subjects you like to shoot. If you like landscape or scenery photography, you’ll definitely find the wide-angle capability of full frame cameras useful. They also perform better in low-light situation because their sensors tend to show less noise at high-ISO than their crop counterparts. The high-ISO feature itself is also helpful for night time sports photography where low-light and fast shutter speed requirements limit your options that you could otherwise have employed.
On the other hand, although that extra field of view provided by full frame sensor comes in handy in many situations, it may actually be a disadvantage if you are shooting wild life photos or any photos that requires a telephoto lens. Because of the crop factor, crop sensor cameras have a somewhat longer “reach” than the full frame cameras, and that helps photographers to see the subjects better and to quickly compose the photos in details before their subjects slip away. Furthermore, all the above-mentioned advantages the full frames have also make them a lot more expensive to make, and that may be a turn-down for many beginners or photographers on limited budgets.
One last thing to keep in mind, is that while all lenses made for full frame cameras can also be used on crop sensor bodies, lenses that are specifically made for crop sensor cameras cannot be used on full frame bodies because they were not design for the wide field of view the full frames have. If you use a crop sensor lens on a full frame body, you’ll notice how the scenes are reflected in the center of the images, but the other parts of images are black.