Take a Lumia 920 and slap on an AMOLED screen, and you have a Lumia 925 or 928. Take a Lumia 920 and slap on an AMOLED screen and a hulking great camera—now you have the Lumia 1020.

The Lumia 1020 is Nokia's new flagship Windows Phone. It's a mix of the familiar and the novel. Familiar are the phone's internals, sensors, and screen. There's the same dual core 1.5GHz Qualcomm Snapdragon S4 as found in the 920, 925, and 928. The same 4.5-inch 1280×768 AMOLED screen as the 925 and 928 with the same Gorilla Glass coating and "PureMotion HD+" that's supposed to reduce reflections, improve sunlight visibility, and ensure crisp 60Hz screen updates.

Even the design is very familiar. From most angles, it looks just like the Lumia 920. The body is seamless polycarbonate (black, white, or yellow) with a slightly curved black screen on the front. The right-hand side has a set of buttons: power, volume, and a camera button with half-press focus.

There are a few minor internal differences. The Lumia 1020 has 2GB of RAM instead of the 1GB found on the 920-series phones. It apparently contains a barometer, new to Windows Phone, in addition to the typical GPS/GLONASS, compass, accelerometer, and gyroscope. Slightly peculiarly, it eschews the built-in wireless charging support found on the 920 and 928, instead using a clip-on cover to provide wireless charging, similar to the 925.

But the point of the Lumia 1020 is the camera. If you don't care about smartphone cameras, the Lumia 1020 has nothing significant to offer above the 920 series. I don't think you'll ever notice the extra RAM or barometer.

That camera

If, however, you like taking photos with your smartphone, the Lumia 1020 is altogether more interesting.

Though the Lumia 1020 looks like a 920 in most regards, it has one striking difference: a great big bulge on the back where the camera is.

Small cameras—the kinds found in phones and point-and-shoots—have their imaging sensors measured in an honestly idiotic "inch" system that doesn't actually correspond to the size of the sensor itself. In the 1950s, the analog sensors used in TV cameras used glass tubes. These came in a wide range of diameters, and it's these diameters that are used to denote the size of the imaging sensors. However, the actual usable sensor size in these tubes was about two-thirds of the diameter.

Even though nobody uses video camera tubes any more, these smaller sensors retain the tube-based sizing policy. A sensor described as being 1/3.2", such as that found in the iPhone 5, has a diagonal not of 1 ÷ 3.2 = 0.3125 inches/7.9 mm but rather about two-thirds of that, 0.208 inches/5.28 mm. This isn't exact. The ratios vary, with the iPhone 5's sensor being about 0.233 inches/5.9 mm.

Under this historic, inaccurate, and downright anachronistic measurement system, the Lumia 1020 has a 2/3" sensor. This translates to a diagonal of about 0.444 inches/11.2 mm.

The sensor has a resolution of 7712×5360 for a total of 41.3 megapixels. The optical parts of the camera don't illuminate the corners of the sensor, however. Instead, it supports 16:9 images at 7712×4345 (33.6MP) and 4:3 images at 7136×5360 (38.2MP). Each pixel is 1.1 microns.

As is increasingly common, the sensor is back-side illuminated. Most imaging sensors use front-side illumination: like the human eye, photons have to pass through the sensor's wiring before reaching the photo diode itself. This arrangement is easier to manufacture and more physically robust, but the wires reflect some of the light falling on the sensor, reducing the low-light performance.

Back-side illumination constructs the sensor similar to that of a cephalopod eye, with the wiring behind the photo diode. This is more complex, but it allows more light capture. Apple has used back-side illuminated sensors since the iPhone 4; Nokia uses them in the 920 series' cameras, among others.