Sensor Size and Image Quality
When it comes to digital camera sensors, bigger is DEFINITELY better.
Instead of a sophisticated piece of electronics, think of a digital sensor for a moment as a collection of hollow cylinders arranged in a rectangular grid.
Also imagine - for the sake of simplicity - that the grid consists of 30 horizontal cylinders and 20 vertical ones for a total of 600 cylinders.
The purpose of each one of these cylinders is to gather light so that the light can be converted into an image.
First, let's place all of these cylinders in a rectangle that is limited in width to 120 pixels (I'm using pixels as a unit of measurement to avoid any references to inches vs. millimeters). At only 120 pixels wide, each cylinder can only measure 4 pixels across.
But if we expand the width of the rectangle that contains the cylinders to 240 pixels, then each cylinder can be twice as wide (8 pixels across). Increasing the surface area for the cylinders without increasing their number means that each cylinder can be physically larger.
Digital Sensors and Photosites
Instead of cylinders, digital camera sensors contain millions of individual light-gathering elements called photosites (where a photosite is like the cylinders in the example above).
When a manufacturer creates a camera with a larger sensor, they have two choices:
As I discuss on my page on megapixels, more megapixels are really only necessary if you want to make giant prints. Having more megapixels does NOT make your photos look better.
But why would a manufacter choose to increase the size of the photosites rather than upping the megapixel count?
Once you know the answer, the real benefit of larger sensors becomes apparent: larger photosites DO capture images with higher quality, especially at high ISO settings.
Large photosites produce less noise at high ISO settings, while small photosites produce a ton of noise even at relatively low ISO settings.
Take a look at these two photos.
The photo on the left was captured with a compact camera with a small sensor at ISO 800. Notice the level of speckling - also called image noise - that is visible. The photo on the right was captured with a digital SLR with a large sensor at ISO 800.
Even though the ISO value is the same for both photos, the larger sensor in the DSLR produces less noise.
Sensor Sizes - From Compact to DSLR
Now that you know that the size of a digital sensor can have an impact on the quality of your photos, let's take a look at the different options that are available to you.
There are currently five main sensor sizes in digital cameras:
Since just looking at the numbers is not enough to see the difference in size, the following diagram illustrates the differences (note: these are not the actual sizes of the sensors, but the relative proportions are correct). Since 4/3 and micro 4/3 sensors are so close in size, I have not included regular 4/3 in the diagram.
Remember: the larger the sensor, the less noise you get at high ISO settings. Put another way, you get BETTER image quality across all ISO values when you use a camera with a larger sensor.
The reason that mirrorless DSLR cameras are appealing is because on the outside they have the same size and shape as a compact camera, but on the inside they're hiding sensors that are significantly larger.
This means that you don't need to lug around a giant camera if you want to capture higher-quality photos. It's especially nice to know that you can take pictures in relatively dim light without having to compromise image quality too much.
Great image quality in a small, light package — it's the best of two worlds.
Mirrorless Camera Terms