In the days of film, the most common standard was the 35mm film roll. Any brand that manufactured films made this size in the maximum numbers. Most of the cameras used this size. If your father or grandfather took pictures of you while holding the camera close to the eye, there are very high chances that the camera used a 35mm film roll. Most of the photographers who have been into photography since the film days have used this size. 35mm film is actually 24mm x 36mm in size. Take a note, this means a 2:3 ratio or a 3:2 depending on how you put the length and width of the frame.
During the later stages of film era, came a system of cameras and films which was called Advanced Photo Systems. They had capability of clicking three frame sizes and the Classic size was of 16.7mm x 25.1mm. Again a 2:3 ratio. In short this was called APS-C size. This system did not make to the main stream and was soon overtaken by the digital revolution in photography.
Sensors which have now replaced films are an expensive piece of electronics to manufacture. Sensors consist of small pits where each of the pit equals one pixel in layman terms. (This is similar to how photoreceptors in our eyes correspond to each distinct point that can be seen. More on this – Our Eyes vs Camera).
Now we have the same old common formats duplicated in the sensor sizes. The 35mm sensor size is commonly called as ‘full-frame’ and the APS-C sensor is commonly called ‘crop-sensor’. Both have their advantages and disadvantages. There are cameras with still smaller sensors and those with bigger sensors but we will not include them in the discussion here.
(Representation of ‘Image Circle’ or the circular field of view projected by a lens. Area of a Full Frame Sensor marked by the outer rectangle and APS-C Sensor by the inner rectangle.)
APS-C or Crop Sensor Cameras
These sensors are comparatively cheaper to produce and are obviously smaller in size. The cheap production cost translates to lower selling price. Lower selling price helps in more sales and further helps the company to mark the price low. This is economics in play and as a result these cameras cost lower than their full-frame cousins.
Smaller size also means that the electronics can now be placed in a smaller case and the resulting cameras are therefore usually smaller and lighter than full-frame cameras… easy for people with small hands or fingers to use. I have found that most painters, surgeons and people involved with fine work prefer these smaller camera bodies over the full-sensor large camera bodies. It may be a false perception but this is what I have generally seen in my interaction with photographers and hobbyists. I always recommend that a photographer should use a camera that feels more natural while holding and the controls are comfortable to reach for with minimum efforts.
The sensor size leads to cropping of the image or a sense of magnification. This is represented by a multiplier which is used to multiply the focal length of the lens to get an idea of what focal length will give the same angle of view on a full frame. Nikon has a multiplier of 1.5 to get this idea. What it means is that a 18mm end of the usual 18-55mm kit lens on a crop sensor camera body is almost same as a 28mm (actually 27mm) lens on a full frame body. This is good when you consider wild-life or bird photography. A 150-500mm lens translates to an equivalent focal length of 225-750mm when it comes to angle of view. Smaller sensor means that the lens used to create the image circle can be smaller in size and so the corresponding lenses are also inexpensive.
Another advantage of the smaller sensor is the ease of focusing. When the above effective focal length is calculated the other way round, it becomes obvious that to achieve an angle of view similar to a 50mm lens on a full-frame, a 33.3mm lens will be required on a crop sensor camera. The smaller the focal length, the wider the lens covers and in turn leads to increased depth of field. Greater area in front and behind the focal point appears sharp and so the focusing is easier. (Go to the extreme small sensors found in phones and you’ll now understand why everything appears focused in photos clicked with these phone camera. More on phone cameras –Phone camera for photography)
All the lenses that work on full-frame cameras also work on crop sensor cameras. There may be other issues like presence or absence of focusing motor, electronic contacts etc but as far as image circle goes, the lenses meant for full frame cameras can easily provide the image for the smaller sensor too. Is that not logical? In fact, some of the average lenses which are too soft at corners with the full frame cameras, give excellent results with the crop sensor cameras since the soft periphery of the image circle get discarded.
Sensors generate heat and this heat converts into noise. Larger sensors tend to heat up faster than the smaller one. So for video users and those who intend to use liveview quite a lot, I recommend crop sensor cameras. (Remove Noise, Add Grain)
Crop sensors also force one to move back while using a lens to get in more of the area. This changes the perspective. Portraits taken with a 105mm lens on a crop sensor come out looking better than the same composition on a full-frame camera. I’ll discuss about perspective in another post.
Full Frame Cameras
The cameras are larger and heavier in general than the APS-C sensor cameras. For me this is a big plus. I have thick fingers and I really appreciate the comfort of being able to reach out for controls without pressing any unwanted buttons. Heavy cameras are somehow more stable for me to use and I can click at comparatively low shutter speeds while holding in hands. When I walk for long distances, I do still wish that I had a lighter camera.
The larger sensor covers more area and so they are useful for really wide shots.
Due to the larger area, for every image, I have to move a little closer to get a similar composition as a crop sensor camera. This increases the feeling of depth. Very effective in getting the images to look three dimensional.
The full-frame sensor requires a larger focal length to capture the same angle of view as a smaller sensor camera, and so as an opposite to everything being in focus, it is easier to get bokeh or those smooth out of focus areas.
Full-frame sensor with the same resolution as a crop-sensor, theoretically will have larger pixels and so lower chances of noise at high ISO. In fact if you are planning to do a lot of family photography in available light then compare the high ISO performance of low mega-pixel count cameras, using unprocessed raw images and then base your decision on that. However with the advancement of technology now newer cameras with small sensors are also capable of very good high ISO performance.
Full frame sensors with high pixel count on the other hand provide the comfort of cropping the image without loosing out too much of details. This in fact raises another question, especially if you have been attentive till this part of my post- Which is better? A crop sensor camera with a 500mm lens (effective focal length 750mm) or a full-frame camera with a 500mm lens and then the image cropped while post-processing to match the size of a 750mm lens? 😉