We all know light sensors make our cameras work, but what makes a good light sensor? Which camera and image sensor combo is best for me and how will it affect the lenses I already own or might buy in the future? This handy guide will help you answer those questions and maybe even learn a few fun facts along the way.
If you would like to get straight to finding the right camera for you, feel free to jump ahead to the camera buying guide below. Before that are some interesting facts about sensors and the science behind them. Light sensors as you know, capture visible light (sometimes invisible light if you’re getting fancy with infrared) and turn it into digital signals.
Light sensors as you know, capture visible light (sometimes invisible light if you’re getting fancy with infrared) and turn it into digital signals.
Although the process is quite complicated, it can be summed up by saying photons that sink into a sensor produce electrons that can be read by your camera’s memory to ‘print’ an image that you can see. Most commonly this is achieved by either a CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor) sensor. CCD sensors record electrons produced by the photoelectric effect then bus them, in sequence, to a camera’s internal memory.
The fact that CCDs move information from the sensor in sequence instead of using parallel processing is important for many reasons and is one of the defining differences between CCD and CMOS sensors. CMOS sensors, which use parallel processing, provide for higher speeds and lower power consumption. They do have drawbacks like rolling shutter and higher noise, but as of late CMOS sensors have largely replaced the older CCD sensors.
Because of their advantages and advancing camera software’s ability to mitigate the negative drawbacks, CMOS has come to dominate the digital camera market. For more in-depth information about the science behind camera sensors, this article provides a comprehensive overview of both CCD and CMOS sensors.
Getting the Right Image Sensor for Your Needs
First things first; the question you have to ask yourself is how much resolution do I need? If you are working with print or other large-scale applications, where fidelity is key– you have to be considering the larger-end sensors. Somewhat intuitively, a larger sensor returns a larger image, giving you better resolution and more space to zoom, crop and/or print without losing fidelity. If your uses will be mainly on the web or in digital format you can get away with smaller sensors and still produce high-quality images.
For video, printing fidelity is obviously not an issue, but there are other factors that may make a larger sensor more desirable. For instance, larger sensors generally perform better in poor lighting conditions and are capable of producing more intense background blur. Crop factor and lens choice will also come into play, as discussed later in this article.
Dynamic range (DR), defined as the range an image sensor can capture the strongest undistorted signal (the brightest areas) and the weakest undistorted signal (the dark areas) in an image, is also very important to consider. In photography, this range can be augmented with the HDR (High Dynamic Range) function, now featured in most cameras. But in video, a sensor’s DR still plays an important role. Given the fact that video is continuous, (most) cameras cannot expose for several different levels at the same time and a sensors DR still depicts how much detail a camera can retain in high contrast scenes. RED’s HDRx is an exception since this shooting mode allows RED cameras to shoot two exposures for each frame.
Your sensor’s dynamic range also plays a large role in how well your camera will be able to capture low light situations as well. If you know you need a versatile camera that can shoot high contrast scenes like objects in front of a bright sky or in low light situations, a larger sensor size is the right option for you.
Lens and Sensor Combos
When considering sensors and lens sizes, consider that sensors smaller than the baseline 35mm shift the focal length of a lens to be more telephoto. For example, when using a Canon with an APS-C size sensor like those in the Rebel series, all of your lenses zoom in by a factor of 1.6, making a 50mm become an 80mm, a 70mm becomes a 112mm and so on. This limits your wide-angle capability and should be a major factor in considering what size sensor is right for you. The graph below should illuminate how a sensor will change the size of the lens that you already own or may buy in the future.
An item to note as well is that, contrary to popular belief, a sensor does not change a lens’ depth-of-field, though the focal length of the lens you are able to use to get the shot you want will influence the appearance of the background blur in your image. The cropped image may also force to you move farther away from a subject to achieve the same shot a full frame sensor would give you in the original position.
Solutions for Smaller Sensors
Once you have considered all of your needs and the sensor that might be right for you, don’t forget that there are many software options that can help you save money by allowing you to select a slightly subpar sensor for your needs. Perhaps you know you will need a large sensor for low light situations but can’t afford a full frame camera. Software like Neat Video (which I personally use) and other denoising filters and plug-ins can clean up dirty footage to a great degree, letting you use a smaller sensor while still providing a high-quality image.
If perhaps you have prime lenses that offer very wide apertures, this could also help capture low light situations on a smaller sensor with less noise.
Overall, when considering different cameras and their sensors, draw up a diagram of your needs, expectations and budget. Shop with these factors in mind and you are sure to find the right camera to suit your work.
Sky Scholfield has been producing videos for clients including National Public Radio, The Smithsonian and NGOs throughout Northern California for over ten years. He is now producing a documentary film about the Pit-River Tribe in Northern California