Tech companies love to wave big numbers and fancy sounding words around in their ads, and camera manufacturers are no exception. Although it isn’t as bad as it was a few years ago, “megapixels” is normally their go-to buzzword. But what is a megapixel and does more really mean better? Let’s find out.
What Are Megapixels?
On every digital camera sensor, there are tiny little “photosites”. Each of these is a sensor for a single pixel. When light hits a photosite, it determines what color that pixel should be in the resulting photo. Obviously you need lots of photosites to get a high resolution image; one million photosites will give you one million pixels—or one megapixel—in the final image. This means a 20MP photo was taken with a camera that had a sensor with twenty million photosites.
Megapixels and Sensor Size
The sensors in digital cameras come in different sizes. The sensor inside your smartphone is smaller than the sensor inside a crop sensor camera and the sensor inside a crop sensor camera is smaller again than the sensor inside a full-frame DSLR.
All three of these cameras, however, can have a 12MP sensor. What changes is the size of the photosites on the sensor. On a smartphone camera, they’re tiny, while on a full-frame camera, they’ll be much much larger. This affects the overall image quality.
The Pros and Cons of High Megapixels
The size of the photosites is very important for image quality and low light performance. While the technology has come a long way over the last few years, and it’s now possible to cram more photosites than ever onto a sensor, there are pros and cons to it.
The more megapixels a sensor has, the bigger the image it can create. This is really useful for fashion and studio photographers who want every single detail, such as the subject’s eyelashes, as clearly as they can capture.
Higher resolution sensors also make it possible to print larger photos, although that isn’t as big a deal as it used to be. As Apple has demonstrated, you can make billboards from 12MP smartphone images.
A camera with a lot of megapixels is also more forgiving to use. If you stand too far back from your subject when you take the photo, you’ve more flexibility to crop in close and still have a decent size image.
The downside is that, with smaller photosites, you have worse low light performance. Since sensor size doesn’t change, a 20MP and a 50MP camera will have the same amount of light to work with. The photosites on the 20MP sensor will each get about twice as much light falling on them as those in the 50MP sensor.
With large images also comes large file sizes. A 20MP image shot with a DSLR will often be about 25MB; with a 50MP image, the file size more than doubles to about 60MB. This not only means you need more storage (which is cheap), but more processing power in your computer to edit them efficiently (which often isn’t cheap).
What Is the Sweet Spot?
Right now, any modern camera has enough megapixels for almost anything you could want to do. It’s no longer the differentiator it once was and, once you get passed a certain point, other factors start to become more important.
Smartphones seem to have settled for around 12MP sensors over the last few years. The iPhone 7, Google Pixel, and Samsung Galaxy S8 all have sensors of about this size. This seems to be a bit of a goldilocks spot in terms of image size and low light performance for small sensors. You get an image big enough to do what you want with, and they aren’t absolutely awful in low light. Cheaper phones with lower resolution sensors, and thus larger photosites, don’t have better low light performance; they generally just have worse cameras.
For crop sensor DSLRs, around 20MP is a great ballpark. Canon and Nikon offer cameras with sensors between 18MP and 24MP. That’s obviously more than big enough for almost anything, but the photosites are still large enough that the low light performance tends to be okay.
Full frame DSLRs have much larger sensors so can handle more megapixels. This has led to a split in the models offered. While there are super high resolution cameras with 50MP+ sensors; these are best for specialist uses in ideal settings like fashion photography in a studio. Both Canon and Nikon seem to have settled on around 30MP as the best balance between file size and low light performance for their flagship models.
Right now, buying something because it has more megapixels isn’t the best idea. Instead, try to stick to those sweet spots for the sensor in your camera. You won’t go far wrong. Stepping outside of these means you’re getting into more specialist territory and will start to see the downsides of having too many megapixels.
Image Credits: Torbakhopper via Flickr