Sensor Size Mythology

There is a lot of misinformation going around about sensor size and many seem to believe that “full-frame” is the end-all be-all of sensor sizes and photographic nirvana. I’ve already discussed this myth here. But I thought I would approach this sensor-size envy from another angle today.

You should already know that pixel size has a direct impact on the quality of a sensor. Each pixel can be thought of as a little bucket that accumulates photons of visible light. All else being equal, the bigger the bucket, the higher the sensitivity, the lower the noise, the bigger the dynamic range and the better the colour depth. I say all else being equal because the fact is that sensor technology including both the light detecting cells themselves and the surrounding circuitry like amplifiers and processors are constantly improving. So today’s sensors can have much higher pixel densities (smaller pixel size) and still perform the same or better as far larger pixels from a few years ago. Case in point, compare my full-frame Nikon D700 12.1 megapixel sensor from 2008 with a current MFT 16 megapixel sensor that has 5 times the pixel density yet very similar performance.

sensor size diagram aps-c four thirds nikon cx one inch iphone 5This is why we can now have smartphones (which have tiny sensors) with 16 megapixels and really decent performance (mind you, I think smartphone manufacturers would be much better off sticking with 8 Mpixels but marketing obliges). And this is the crux of my point: the most popular camera today, both by number of users and the number of pictures posted to sites like Flickr, is the iPhone. Now an iPhone 6 has a 1/3″ sensor and the 5S a 1/3.2″ sensor. Look at the chart above to see how small that is. Yet millions of people are perfectly happy, even amazed, with the quality of their smartphone pictures. They do have a point as the best camera is the one you actually have with you and most of them will never make large prints anyway.

Personally I think the smallest sensor size that provides adequate image quality for a serious (as opposed to casual) camera today is the 1″ sensor. These sensors have 6 to 7 times more surface area than the iPhone sensors but only half the area of an M4/3 sensor or 1/8th the area of a FF sensor. Looking at it from the other way, while the M4/3 sensor has only 26% of the surface area of a FF sensor and 60% of the area of an APS-C sensor, it does have twice the area of a 1″ sensor, some of which are considered excellent like the one in the Sony RX100 series. The M4/3 sensor also has a whopping 13 times more surface area than the world’s most popular camera, the iPhone.

So once again, the whole sensor size thing is very relative and it is a moving target (improving significantly with each new sensor generation). If you want the ultimate in image quality and shallow depth-of-field (DOF) why stop at FF, why not go Medium-Format? If you want something that is lighter and more portable, why not go for a 1″ or M4/3 format? And if you want the ultimate in pocketability then get yourself something even smaller like a smartphone. All have their advantages and disadvantages.

To me, for my needs and priorities, the M4/3 system hits the sweet spot. A FF camera system is just too bulky. An APS-C system, while somewhat smaller, still uses relatively large lenses that are not significantly smaller than the FF lenses. The 1″ systems make it a little too hard to get some shallow DOF. The M4/3 system to me strike the perfect balance of image quality, creative flexibility, cost and system compactness.

Note that I’m talking about system compactness here and not camera compactness. Sony has already shown us that with mirrorless technology it is possible to make very compact APS-C cameras (like the A6300) and even full-frame cameras (like the RX-1). On the other hand you can only make cameras so small before they become awkward to use. In reality the size, weight and cost of the lenses has a much greater impact on your system than the camera itself. This is the secret that allows you to build a complete M4/3 kit that weighs only 3 or 4 lbs, something that you just cannot do with APS-C or FF systems because of their lenses.