Even if it is a crucial thing for the quality of photos, most ordinary photographers are ignorant of the image sensor size they use.
Image sensor size is the most important factor of the camera’s cost. Manufacturers tend to conceal it and focus their marketing on other specifications. In the case of small cameras doesn’t even exist on their manuals and brochures. Consumer compare megapixel, body size, weight, optical zoom, connectivity and forget the most important which is the image sensor’s size.
Image sensors are cut from a big silicon disk called wafer. Silicon wafers are expensive. VERY EXPENSIVE. Usually only one in three wafers is pure enough to make sensors. A wafer can be cut in more smaller sensors than big ones. Since the wafer is circular bigger rectangular sensors create more waste space at the disk edges than smaller ones. So a small image sensor is by far more cheap than a bigger one and more profitable. Big sensors shouldn’t be related with more megapixels. Actually what counts more is the size of every individual pixel than the total amount of them. A bigger pixel receives more light than a smaller one. More light reduce the need of higher sensitivity ISO. Low ISO produce lower image noise and sharper images. Image noise is the equivalent of the grain in high ISO films. Big sensors are ideal in low light photography. That’s the reason why mobile phones no matter how expensive they are shot low quality photographs under poor lighting. It is impossible to insert a large sensor in such a slim device.
Big image sensors require bigger lenses in diameter. The bigger the elements of a lens the more expensive they are. That doesn’t have to do with the cost of the material like in the silicon wafers case. When an element of a lense is big requires more time and effort to be perfectly polished and multi layered than a smaller one. Imperfections are more visible, like barrel distortion, chromatic aberration, sharpness, flaring, clarity etc. Larger lenses are exponentially more expensive from small ones of the same materials and technology. For example full frame cameras have bigge lenses in diameter than crop sized compact cameras.
Under normal conditions the difference between small or bigger sensors is negligible. Outdoor daylight photography without shadows, or well lighted indoor photography doesn’t demand big sensors.
An iPhone can shot decent but boring photographs under ideal lighting. Impressive photographs are under special lighting. Sunset or sunrise, blue hour, artificial lighting in sports et are very demanding. A bigger sensor offers creativity to the photographer.
The bigger sensors have better dynamic range. Dynamic range is the difference of the amount of light the sensor receives from the brightest and darkest areas.
A classic example is photos during sunny middays. The shadowy and the bright areas can’t be captured equally well. In this case there is a large dynamic range of light. During a cloudy day there aren’t any shadows and the dynamic range is small. The large pixels of a large sensor copes with this problem better.
The size of a digital image sensor varies a lot. However for compability reasons with legacy lenses of the film era the main sensor is the full frame one. The full frame sensor has the same size of a 35mm film, 36mm length X 24mm width. Its aspect radio is 3:2. The aspect radio of 3:2 is considered the standar in photography. The 35mm film is named from the width of the perforated film gauge. 24mm width + 11mm holes = 35mm. The full frame sensor is considered big today. However the 35mm film was also known as small format film for amateur in comparison to professional medium format and large format films of the film era. The compatible lenses for full frame digital cameras are named EF by Canon and AF-S by Nikon.
The APS-C sensor size derives from the APS film. Advanced Photo System type Classic was introduced in 1996 a few years before the expansion of digital cameras. Its classic type size was 25.1mm × 16.7mm. It had a magnetic coating that could store informations like shutter speed, aperture size, aspect ratio etc. It was created to be more practical but not better than 35mm film. It was short lived. By 2002 the compact digital cameras were cheap enough to replace APS film cameras but not 35mm cameras yet. First mass produced digital SLR cameras appeared the early 2000. They were not affordable by anyone at the begging. Despite being compatible with 35mm lenses, they didn’t have full frame sensors. That came later. The size of the first dSLR sensors was similar to the APS-C. Even nowadays most dDSLRs have APS-C sensors because they are easier to be mass produced and offer good quality. Also most lenses are constructed for APS-C sized sensors. Canon name them EF-S and Nikon AF-S DX.
Every digital sensor bigger than full format (35mm) is named medium format. Medium format films were the choice of professionals. The 35mm film was inferior but cheap and good enough for amateurs. Medium format digital cameras are still very expensive. They have the same price of a car. Their quality is second to none. They offer by far more megapixels without reducing the size of pixels. Their Dynamic Range is perfect as their sharpness and light sensitivity. Additionally these lenses are not mass produced. That makes them very expensive. It’s a niche market. The dominant Canon and Nikon brands haven’t ever created a medium format digital camera. The both very prestigious and historical German Leica and Danish Hasselbald offer medium format digital cameras. These are cameras for the very successful professional photographers or the uber rich amateurs.
Micro Four-thirds sensor size doesn’t derive from a film size but from the 4/3 inch diameter of the common video camera tube. The standard aspect ratio of glass TV sets was 4:3. A Micro four third sensor has 17.3mm length and 13mm width. It is inferior than the previous sensor sizes. However the recent advances in low noise ISO and dynamic range have created four-thirds sensors with equal quality of a five year old APS-C sensor. The first mirrorless digital cameras in 2008 had a micro four-thirds sensor. Most mirrorless cameras still have micro four-thirds sensor. It is the only decent solution in high quality small cameras with reasonable price. It saved brands like Olympus, Fujifilm, Panasonic, Samsung that couldn’t compete with Nikon and Canon at the dSLR sector.
1″ sensor is a the more recent popular sensor size. The size of one inch sensor is 13.2mm length X 8.8mm. Nikon names it CX format and puts it in his mirroless cameras. Sony uses it in his premium compact and super zoom cameras like the series of compact Sony Cyber-shot DSC-RX100 and super zoom Sony Cyber-shot DSC-RX10. The one inch sensor is the smallest size for serious photography. Mobile phone after 2007 with first iPhone had gradually elbowed the digital compact cameras with tiny sensors. The 1″ inch sensor is big enough for quality photos and small enough to be inserted into small compact or mirrorless camera. It has reopen the gap between mobile phones and very small digital cameras.
Smaller sensors are measured in fractions of the inch. For example the legendary Nokia Lumia 1020 mobile phone has a 2/3″ 8.8mm X 6.6mm image sensor with the amazing 41.3 megapixel. The iPhone 5 with its decent camera has a 1/3.2″ 4.54mm X 3.42mm sensor. The iPhone 6 plus with its electronically stabilized lens has a 1/3″ 4.8mm X 3.6mm image sensor.
Crop factor is relative to size of an image sensor. Crop factor or Focal Length Multiplier FLM is the ratio of the diagonal length of a full frame image sensor to the diagonal length of the actual image sensor. The typical diagonal length of image sensors are: Full Frame 43.2mm, APS-C 30.1mm and Micro 4/3 21.6mm. For example if the camera has a full frame lens its crop factor is (43.2/43.2=1) 1. If the camera has an APS-C sensor then the ratio is (43.2/30.1=1.43) 1.4 crop factor. If the camera has a micro 4/3 sensors then the ratio is (43.2/21.6=2) 2 crop factor. That ratio in practice affects the field of view of the lens. In simple words a 100mm lens of a full frame (crop factor 1) camera when is put on a APS-C (crop factor 1.43) camera acts like a (100 X 1.43 = 143) 143mm lens. On a micro four thirds camera (crop factor 2) it acts like a (100 X 2 = 200) 200 mm lens. The smaller the sensor the more powerful a telephoto lens is. Super zoom compact cameras have small image sensors in order to avoid lengthy lenses.
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