Retina Display is the name for the high-resolution screen technology Apple uses on various models of the iPhone, iPad, and other Apple products. It was introduced with the iPhone 4 in June 2010 ...

In other words, how many pixels per inch depends on the size and resolution of the screen you're talking about, so we'll have to do some math to get the number you're after for yours.

Pixel binning may be the latest buzzword in consumer tech, but astroimagers know the technique has been around since the dawn of charge-coupled devices.