How Big Are My Pixels?
January 21, 2010
In the firestorm of comments about the Great Megapixel Swindle, a couple of questions kept coming up: “Instead of megapixels, what should I be looking at? And how do I even know what chip size a camera has?”
Well, cameramakers designate chip sizes using an almost incomprehensible naming system (inherited from video tubes, if you really must know) using numbers like 1/2.3″. In fact, if we don our conspiracy tinfoil hats, it’s almost as if they’re deliberately making it hard to understand the true size.
Thankfully there’s a table decoding various sensor formats here. (Though that page has grown a little dated: There are no longer any 2/3″-sensor models on the market, sadly.)
But the number I really care about is, what is the size of the pixels? Yes, new technology might still come up with a few sensitivity-enhancing tweaks. But loosely speaking, the bigger each pixel is, the better.
Pixel width is quoted in microns—sometimes abbreviated µm or um. But it’s not often listed directly in camera specs.
But many in-depth review sites like DPRreview will give the “pixel density” in their model listings. Note the ridiculous jump from the consumer point & shoots (between 35 and 50 megapixels per square centimeter) versus the serious DSLRs (1.4 to 3.3).
Might this tell us something?
So as a handy conversion reference, here’s how to translate some of those density numbers into actual pixel sizes*
- 50 Mp/sq. cm —> 1.4 micron pixels
[e.g. 14-megapixel compacts]
- 35 Mp/sq. cm —> 1.7 micron pixels
- 24 Mp/sq. cm —> 2.0 micron pixels
[“enthusiast” compacts, e.g Panasonic LX3]
- 16 Mp/sq. cm —> 2.5 micron pixels
[Fujifilm F31fd, circa 2007]
- 5 Mp/sq. cm —> 4.3 micron pixels
[New micro Four Thirds models]
- 3.3 Mp/sq. cm —> 5.5 micron pixels
[typical APS-C sensor DSLR]
- 1.4 Mp/sq. cm —> 8.5 micron pixels
[professional Nikon DSLR]
Now, for the reasons I’ve vented about before, the smallest pixel that makes any sense to me is about 2 microns across. Making cameras pocketable dictates smaller sensor sizes; but unless the chip is under 24 Mp/sq. cm, you’ll definitely compromise low-light capability.
But the real leap in quality comes when you drop to “single digits” in pixel density. Even compared to enthusiast compacts, those DSLR-style pixels have 5 to 8 times the light-gathering surface. That really makes a difference.
What this world needs badly is more little cameras with big pixels. I hope we get some soon.
*Note I’m really quoting the “pixel pitch.” Each actual pixel loses a bit of light-gathering area to its wiring traces. But microlenses overtop give nearly 100% coverage; and so they’re really the relevant width in terms of light-gathering area.