As of Summer 2009, if you step up to digital single reflex lens (DSLR) photography, you have two basic choices: cameras with full frame sensors and cameras with 'cropped' sensors. Full frame sensors are roughly the same size as the 35mm film. The cropped sensors (they come in two sizes APS-C and four thirds) are smaller - by a crop 'factor'. The most popular DSLR cameras (at least by volume sold) are the those equipped with an APS-C sensor. The crop factor varies, but it is generally 1.5 to 1.6. What this means is that an APS-C sensor is 1.5 (or 1.6) times smaller than a full size sensor. Both types can use legacy SLR lenses. So which way should one go? Here are the relative advantages:
APS-C (or in Nikon parlance, DX):
- Increased range at the telephoto end. For example, for a 200mm lens on an APS-C sensor, the angle of view and magnification would be similar to a 300mm lens on a full frame sensor. Not bad if you're a wildlife photographer.
- A new breed of DX only lenses. Since these lenses have to cover a smaller sensor, they can be made smaller and lighter (everything else being equal - and by that I mean mostly their light gathering abilities). Smaller and lighter means you need to haul less equipment and attract less attention from your subjects.
- Cheaper lenses. Smaller and lighter usually means cheaper as well. For example the 12-24mm DX Nikon lens is about $700 and 1 pound in weight, whereas the Nikon 14-24mm full frame lens will set you back $1900 and it weighs a whopping 2.2 pounds.
- Increased depth of field at a given focal length. Lens design at wider focal lenghts usually has the advantage of a deeper depth of field (everything else - particularly aperture, being equal). In other words, if you shoot the same scene with a 35mm prime lens on a DX sensor you usually get more in focus at the same aperture than if you shoot that scene with a 50mm prime on a FX (full frame) sensor. This should appeal to some, but not all situations.
- Everything else being equal, less vignetting (a.k.a. light falloff). Because cropped sensors only use the center portion of a lens, they will likely be less affected by light falloff in the corners.
- Slightly better image quality from full frame lenses. This is a gross generalization, but typically, lenses are designed to be at their sharpest and distortion free in the middle.
- Cheaper cameras. Big sensors are expensive to make - as of now, the premium between the most expensive APS-C camera and the cheapest full frame camera is anywhere between $700 to $1000. The chepest FX cameras available today start around $2000 new.
- Smaller, lighter cameras. Bigger sensors need bigger cameras - and that adds weight to the stuff you have to carry. Add the extra weight from bigger lenses and you go from carrying 2-3 pounds (camera and 2 -3 lenses) to 4-8 if you opt for FX.
Full frame (or in Nikon parlance, FX):
- Increased depth of field as compared to images taken with corresponding lenses on DX. This is very desirable for portraiture, as well as for situations where out of focus backgrounds (bokeh) is used in composition.
- Extreme wide angle lenses stay extreme. 12mm on a FX sensor looks ultra wide angle, while on DX it would look only moderately so (12mm x 1.5 = 18mm). Wacky compositions stay wacky and interior spaces look cavernous.
- Bigger viewfinders. When migrating from point and shoot digital cameras to DSLRs, the first thing one notices is how radically different photographic composition becomes. You go from framing your shot on a nice, bright 2.5 inch screen to looking through a dim, small viewfinder. Nasty surprises - picture ruining details that you just didn't see through the viewfinder, are much easier to avoid using a bigger viewfinder.
- Better image quality (IQ). Everything else being equal - namely megapixels and sensor design, a bigger sensor means proportionally more light hitting it. More light means less noise at the same settings. This really becomes apparent at higher ISOs. State of the art full frame sensors allow the photographer to increase the ISO by 1 or 2 stops without sacrificing the image quality (as compared to cropped sensor sensors). Lower noise is just the beginning - more light also positively affects color depth (you get more vibrant colors that accurately reflect what one sees) and dynamic range (hard to explain in a few words - but basically how large the spectrum of light is between the lightest tones and the darkest tones a sensor can capture). This benefit really only kicks in for low light photography and for high dynamic range scenes (anything with strong light). However, this is more important than you think; if one would shoot in perfect light all the time, one would not need a DSLR period. Any cheap point and shoot can produce comparable results with the most expensive full frame DSLR in perfect light. The catch is - perfect light is hard to get.
So which way should you go? It depends on what and how you shoot. If you shoot a lot of distant subjects, have a tight budget and want to travel light, go for a cropped sensor lens. If you can swallow the price premium, don't mind the extra weight of the equipment, and you often find yourself wanting to explore scenes with less than perfect light, go full frame. For me, going full frame made sense, mostly for the IQ and ease of composition aspects. Looking through a horribly small viewfinder was just too frustrating. I also shoot a lot of low light scenes, so getting acceptable results there was important.
