Helping You Making Sense (and Cents) of Sensors

April 20, 2016 / Uncategorized

Unless you are an advanced hobbyist, semi-professional, or professional photographer you could probably care less about the internal workings of your camera body (the part of the camera minus the lens…and the strap). Should you care about such gadgetry, let us turn our attention to the topic of sensors.

In the old days we had film. Everyone knew what film was because you could touch and manipulate it; as a matter of fact, you had to do so every time you loaded it into, or removed it from, the camera. With the advent of the DSLR (Digital Single Lens Reflex) camera the “film” is out of sight and out of mind. DSLR cameras do not have film; they have sensors. Sensors are flat electronic devices that have the capability to capture light and convert that light into an electronic code that is “written” to the memory card of the camera

Colors, Colors, Everywhere

You press the shutter button and assume that all those gorgeous reds, greens, blues, yellows, violets, indigos, and oranges are magically recorded on the memory card. Well, not quite. For that to happen you would have to have and infinite number individual photocells at every site on the sensor to record all the possible options. In other words, your sensor would be somewhat the size of O’Hare Airport; not very practical, huh? Engineers figured out a way to reduce this size by using primary colors and ratios. Here is how it works:

Sensors with 24 million pixels make the details of this bouquet of red roses and white lilies jump off the page.

A Christmas wedding is the perfect time for a bouquet made of white lilies and red roses

Every sensor has a fixed number of photocells (tiny sensors that read light) called pixels. Most cameras will advertise how many pixels are included on its sensor in units called megapixels. “Mega” is the metric term for million, so a camera that is advertised as a 12 megapixel camera will have 12,000,000 photoreceptors on the sensor while a 36 megapixel camera will have 36,000,000 photoreceptors. I will discuss the implications, advantages, and disadvantages of those numbers later.

Pixels only see intensity of light, not color; kind of like seeing black, white, and all the shades of grey in between. So, how do we get the color photographs if the pixels only see the brightness or darkness of light?

Ratios

Interpreting color is all about ratios. Pixels are grouped into clusters of 4. Each cluster of 4 pixels has a pattern of filters over it that allows the cluster to see light as a mixture of color ratios. Each cluster of 4 pixels will have 1 red filter, 1 blue filter, and 2 green filters on them. This is called the Bayer filter. The camera’s computer will read the ratio of blue to green to red light from each cluster and derive an assigned color based on the ratio of intensities allowed through each filter. If you are wondering where anyone would come up with this idea, then look no further than God Himself. The human eye operates on this very same principal having only red, blue, and green photoreceptors (cones) which still allow us to see an infinite number of colors.  Just to note, there are twice as many green filters because the human eye is most sensitive to green light.

Size Matters

What is the advantage (or disadvantage) of having more megapixels? More is always better, right? Maybe…maybe not. It depends on your needs. Let me explain. Most all sensors in DLSR cameras come in one of two sizes. Small and large. The smaller sensors are called crop sensors and are approximately 16 mm tall by 24 mm wide while the bigger sensor are called full-frame sensors and are about 24 mm tall by 36 mm wide (which just happens to be the approximate size of a 35 mm film negative).

Let’s compare two sensors that are both 12 MP sensors: one is a crop sensor and the other is a full-frame sensor. If you put 12 million pixels on a smaller sensor the pixels are going to have to be smaller, right? While the same amount of pixels on a full-frame sensor will still give you 12 million data points on the image. So why have bigger pixels?

Here is where the size matters. Smaller pixels cannot gather as much light as large pixels can. Think of it as collecting rain. If you put a bathtub out in your lawn in a rainstorm and right beside it you put a test tube standing upright they will both catch water, as a matter of fact, they should both catch the same inches of water. If the bathtub collects one inch of water in the bottom of it the test tube will also collect one inch of water in the bottom of it; but the quantity of water will be vastly different. The bathtub will have much more water in it than the test tube. This same analogy applies to pixels. A large pixel will gather more light than a small pixel; therefore, the larger pixels will operate better in low light situations.

As a professional wedding photographer I want the largest pixels I can afford, because I often have to shoot a ceremony in a venue where I cannot use a flash, so I need all the help I can get to make a good exposure. And larger pixels don’t come cheap. The larger the sensor, the more expensive the camera.

But there are situations where more, smaller pixels are better. If you are a fashion photographer and you want every little hair, skin pore, eye lash, etc. then you want many pixels because more pixels will give you better resolution. Think of resolution as the ability to see and capture fine details. That is not really as important for me as a wedding photographer. I need the ability to photograph in all lighting situations.

The Cost of It All

As I stated earlier, larger pixels are more expensive to produce; therefore, full fame sensor camera are more expensive than crop sensor camera. If you want to go even bigger than full-frame you are taking about “medium format” cameras and the starting price tag can be in the $10,000 range (and up) for the camera body (called the “camera back”) alone. More pixels take up more storage on your computer, slow down the ability of the computer to read, show and manipulate the file and ultimately slow down your workflow. Just because you can afford the shiny new camera, can you also afford more storage drives for those larger files? Will you need a faster processor if you are editing a large number of files at a time?

It is a balancing act. Many professionals will have several camera bodies that cover full-frame sensors with larger, fewer pixels for sports and dim light shooting; full-frame or crop sensor with more pixels for most everyday use; and crop sensors with many pixels better resolution in bright environments.

Summary

If you are looking to buy a new camera consider the following:

Crop Sensors:

Pros                                                                 Cons

less expensive                                                     smaller pixels

good performance for outdoors sports         poor performance for indoor sports

often smaller/lighter camera bodies             often less controls on the camera body

smaller files (if less MP – can vary)

 

Full-Frame Sensors:

Pros                                                                    Cons

bigger pixels                                                          more expensive

often better resolution (portraits/fashion)     often bigger/heavier camera body

better performance for indoor sports              larger files (if more MP – can vary)

often more controls on the body

 

Take if from a professional photographer, don’t be swayed by the “Megapixel War” raged by the camera manufacturers. The first basis for choosing your camera should be selecting the sensor that is right for the job. Please feel free to e-mail me by clicking here and visit my blog by clicking here. I would love to hear from you if you have any questions on this or any other topic.