Photography Basics - Sensor Size

For the first post on the Photography Basic's series, I thought I would start with the so called "brain" of digital cameras, which of course is the sensor. This item one of the most important features inside the camera body, as it is the thing that actually "sees" or senses the images you capture. Sensors come in a large variety of shapes and sizes, and even employ many different ways of capturing light. I will briefly cover these points, but the main focus will be on how sensor size in a camera affects the images it takes.

First some basics. In film cameras, the frames of film act as the light sensitive medium which capture the image. In digital cameras, the film is replaced by a light sensitive sensor, and becomes permanent in contrast to the single use frames of film. Sensors in digital cameras primarily use either a CCD (Charged Coupled Device) or CMOS (Complementary metal–oxide–semiconductor), both of which of course have their positive and negative points, but these are beyond the scope of this article.

The main point I wish to talk about is the size of the sensor, because if you are trying to decide upon a digital camera, its going to come with a sensor regardless, and the more important point is the size of it and how it will affect your images/lens choices.

Sensor size primarily affects two things in images - sensitivity to light, and focal length. The light sensitivity point is fairly simple - the larger the sensor, the more surface area there is for light to be absorbed. But there are also other things that factor into a sensors sensitivity - pixel count, and how closely the pixel sensors are placed together. As cameras pack larger and larger amounts of pixels, or Megapixels onto the sensor, the pixel sensor sizes have to shrink down as well. Of course, sensor technology is always improving making each location more sensitive and tightly packed than before, but lowering the pixel count still counts towards greater sensitivity. This means you can take pictures in darker places without a tripod, or have sharper images in low light conditions. For example, the new Canon 5D MkII, with its 22MP sensor, is bound to be less light sensitive than the older Canon 5D with a 12MP sensor, even though sensor technology has improved for the latter.

If you have ever tried to shoot a photo or video with a small sensor, you might have noticed how bad the photo or footage turned out. Usually in low light situations, the camera will try to raise the ISO or sensitivity levels, sometimes artificially in the case of gain, which makes everything look pixelated and usually riddled with artifacts or noise. The only way to get around this really is to either introduce more light or use a better camera (with a larger sensor).

Because 35mm film has been the standard medium of photography for a very long time, most digital photography terms use 35mm as reference for comparison. 35mm is considered 1:1, at least in the photography world, and a reference of quality. There only exist a few digital cameras that fall into the 35mm (Full Frame) category of sensor size. The first mainstream camera with this size sensor was the Canon 5D, which was followed by the Nikon D700 (There of course were other more professional grade full frame cameras, with more professional price brackets). Because 35mm frame size is used as the reference, lenses and focal lengths are based off this size or field of view. The markings on lenses give their focal lenths in millimeters. The main thing to remember about this is that the measurements are in reference to a full frame sized sensor or 35mm film. What this means, very simply, is that when you use this lens with a sensor that is bigger or smaller than this size, it will give you a different perceived focal length.

The two main sensor sizes from Canon and Nikon are slightly less than 35mm, roughly around 1/4 smaller. This changes the perceived focal length, or Crop Factor. The crop factor of the Canon is 1.6, and Nikon is 1.5, which basically means that the image as seen through a 35mm camera will be cropped down 1.5 or 1.6 times to the center. Although this doesn't physically change the focal length of the lens, it gives an apparent change in focal length as the image will appear more zoomed in. For a lot of point and shoot cameras, they give an apparent rating of the lens - they may give the figure 28mm - 200mm which the range would be on a 35mm camera, but in fact the real lens focal lengths may be 3mm - 46mm, which tells you how incredibly small the sensor in the camera is.

For the general amateur photographer, sensor size may not be that important of an issue. Most point and shoot cameras have sensors barely bigger than a grain of sand (slight exaggeration). But if you upgrade yourself to a DSLR, the main choices you will get will be 4/3 inch, APS-C (Most Canon and Nikon) or Full Frame, in range of sizes. As sensor size increases, the more sensitive your camera will be to light, and the greater perceived size of the image will be.


The other point to keep in mind also is that the larger the sensor size, usually the more money you will have to invest in glass. Lenses for full frame cameras are usually much more expensive, but use higher quality optics and are very rugged. Also, it is much easier to capture wide to very wide angle photos with a full frame camera, since they capture more of the image and you can use lenses with lower focal lengths without getting the crop factor. On the other hand, smaller sensors give you more of a perceived zoom range, as a 200mm lens will give you the equivalent of around 320mm on a Canon/Nikon. As you can see there are positives and negatives to both sides, but most of the positives lie on the larger sensor sizes.

As a side note on the importance of sensor sizes, Red is offering both the Scarlet and Epic bodies with different sensor sizes starting from a 2/3 inch sensor in the Scarlet, through to a Super 35 and Full Frame 35 version. The 2/3 inch version is estimated to be $2,500 for the body, while the Super 35 version jumps up to $7,000. Full frame is a rather expensive $12,000.

The main point it comes down to will be your use for your digital still or film camera. How often will you have to use it in low light situations? Do you want to take ultra wide angle shots, or will be using mostly the other end of the scale with far zooms? With a greater knowledge of the effects of sensor size on photo taking, your camera choices will be more well informed.