Galaxy S7 camera back samsungRafi Letzter/Tech Insider

In technology as in life, bigger is usually better. The iPhone 6s Plus's main selling point is that its screen is nearly an inch larger than the iPhone 6s. A terabyte hard drive is obviously better than a gigabyte hard drive. No one advertises that their headphones are quieter than the competition's.

But cameras are hard to measure in terms of size.

We denote aperture, the most important spec on a smartphone camera, in weird numbers like f/2.2 and f/1.7 — and f/1.7 is actually the better of the two! And even that is only true in some circumstances! The only element of photography where bigger really is better is sensor size, and that hits a hard upper limit in the cramped confines of a thin pocket device.

So tech reviewers without backgrounds in photography zero in on a spec that seems to matter, but really doesn't: megapixels.

Megapixels are a measure of resolution, or the number of individual dots packed onto a camera's sensor. A one-megapixel image has 1 million pixels. If it's perfectly square, that means it'll have 1,000 pixels on each side. That's about the size of a typical image on a website. If you're reading this on an HD screen, you're seeing a smidge more that 2 megapixels. A 4k screen has over 8 megapixels. In order to print an image across the glossy pages of National Geographic you'll want about 10.

You can see then that megapixels do matter up to a point. But every major smartphone brand on the market shot past that point years ago. Still, it's the only measure of a camera most people have heard of or understand. Which is how you end up with statements like this one from CNET's review of the Galaxy S7:

"Although this camera has fewer megapixels than last year's S6, it takes better photos. Scenes are brighter, which makes the action easier to see."

The Galaxy S6 had a 16 megapixel camera. The S7 has 12 megapixels. A reasonable person might assume that would be a disadvantage, but in reality it's an advantage. Let's explore why.

First, megapixel counts on their own have no impact on optics — that's all to do with the lens. Check out these two images:

megapixels qualityRafi Letzter/Tech Insider

I shot both using the same lens, but with different cameras. The one on the left comes from a 12 megapixel Nikon D700, the one on the right from a 36 megapixel Nikon D800. There's no difference in sharpness, color quality, sensor size, aperture, or any other optical effect. The only advantage the D800 has over the D700 is that it'll print magazine-quality images up to the size of my wall, rather than just a large poster. Great for counting pores, but otherwise useless.

(And no, digital zoom doesn't count as a good use if you care about image quality — which, if you're reading this article, I assume you do.)

But high megapixel counts are more than just useless in most circumstances. They can actually be harmful to image quality. The more dots you pack into the tiny area of a smartphone camera sensor, the smaller they have to be. And the smaller they are, the weaker they'll be at accurately detecting light brightness and color.

i tried again under a softer light in a different part of the store but ran into the same problem again the iphone had no trouble in this situationRafi Letzter/Tech Insider

A great example of a smartphone that chased megapixel counts off a quality cliff is the Sony Xperia Z5. Packing and proudly advertising a whopping 23 megapixels — more than Nikon's $6,500 D5 camera — Sony promised a "revolutionary" device. But my comparison revealed a machine that fell well short of the mark. Highlights got blown out, shadows clipped, and the image was actually less sharp than the 12 megapixel iPhone 6s Plus due to imperfections in the lens.

Finally, super-duper-high-res images are just a drag on your storage capacity. The 12 megapixel Galaxy S7 shoots images that hover around 3 megabytes. The 16 megapixel phones make images that nearly double that at 7 or 8 megabytes. That means that a small sacrifice in print size can lead to more than double the photo storage capacity on the same sized card.

Samsung and Apple seem to have found the smartphone sweet spot at 12 megapixels — big enough for beautiful prints, but small enough to retain quality and storage space. Instead focusing on engineering problems like lensing empowers those companies to make the best smartphone cameras on the planet. Expect megapixel counts on other brands' devices to drop as they fight to keep up.