By Evan Coppola (firstname.lastname@example.org), Academy of Scuba Photography Programs Manager and Master Scuba Diver Trainer
At the heart of every digital camera, there is a tiny sensor – roughly the size of a postage stamp or much smaller. There are different technologies used, but every sensor does the same thing: converts light into electrons. Every sensor is made up of millions of microscopic light collectors that work like tiny solar-electric panels.
Photons of light get focused by the lens and strike the millions of tiny collectors of the sensor, which creates electrons. High-energy colors, like blue, make more electrons than low-energy colors like red. The camera’s image processor reads the amount of charge – the number of electrons – produced by each collector and precisely determines the color of light that hit each collector. Each collector yields a tiny dot of color. The image processor combines the dots to form the picture. Each dot is a pixel. The more pixels in the picture, the clearer it is, but it’s never that simple.
Dot quality is as important as quantity. Let’s compare two cameras that both advertise similar resolutions: the entry-level Nikon D3300 (24.2MP, MSRP $599) and the professional-grade Canon EOS 5D Mark III (22.3MP, MSRP $3,399). Canon makes consumer cameras and Nikon makes professional cameras and plenty of other companies make cameras too; I’m not endorsing any brand or model. The 5D Mark III is more than 5 times the price of the D3300 but has fewer pixels. The Canon has some features that appeal to professionals, but the pricing is mainly about the sensors.
A megapixel is one million pixels, so the relatively inexpensive Nikon packs 24 million collectors onto a sensor that is about 23.5mm x 15.6mm (366.60 mm2). This is a common APS-C sensor (Nikon calls it “DX”). The Canon has the same number of dots but arranged on a “full-frame” sensor that is approximately 36mm x 24mm (861.6 mm2) – the same size as a frame of 35mm film (Nikon calls this “FX”). The FX sensor has more than 2.3x the surface area of the DX sensor but the same number of pixels. Logically, each pixel on the larger sensor must be larger.
Think of the sensor as a tile floor with grout between each tile. Bigger tiles means less grout and we need the photons to hit the tiles. Larger collectors gather more photons with a smaller percentage hitting the imaginary grout lines. This creates a better “signal to noise ratio” and clearer, sharper images.
There are many variables that affect overall image quality and dozens of other sizes of sensors being used today. The SeaLife DC1400 and the new MicroHD use much smaller sensors (only about 28 mm2) but still produce excellent, 14MP images. The GoPro Hero 3 Black Edition uses a similar sensor to shoot high-quality 1080p HD video and 12MP stills. The flagship, $6,500 Nikon D4s “only” has 16.2 megapixels on its FX sensor while the Nikon D810 (also FX) has twice that many pixels for half the price. Canon’s EOS 1DX sells for $6,800 with 18.1MP while the $3,400 EOS 5D Mark III we discussed has 22.3. Obviously, the pros value more than pure pixel count. The image processor, battery life, ISO range, lens selection, durability, size, and dozens of other factors can be more critical than resolution if your living is made shooting high-speed sports or wildlife and being able to capture 10 frames per second in tricky light at maximum resolution is the difference between getting the cover photo and getting replaced.
There are practical reasons to want more pixels when cropping, enlarging, and printing your images, but we will address that in upcoming articles along with how your camera’s sensor will affect your choice of lenses for a DSLR.
Figure 1: Relative sizes of three of today’s most common digital camera sensors. Despite the huge difference in size, each is capable of making excellent photographs. Size has very little relationship to the number of megapixels the camera advertises but can impact image quality.
About the Author: Evan Coppola is Academy of Scuba’s Photo Pro. Certified as a PADI Junior Open Water Diver in 1988, Evan enjoyed more than 20 years of recreational diving before moving to the Phoenix area from New England. A former collegiate swimmer, lifeguard, swimming instructor and EMT, Evan joined Academy of Scuba in 2010 to advance his training as both a technical diver and dive professional. He holds the rating of Master Scuba Diver Trainer and is the Manager of Photography Programs and Photographer in Residence at Academy of Scuba. Evan teaches a wide array of specialties, including his passion – Digital Underwater Photography. To support his insatiable lust for world travel, diving and photography, he practices law and teaches scuba. Join Evan on the wonderful journey in becoming an Underwater Photographer.