The PowerShot SX420 IS features a 24–1008 mm (35 mm film equivalent) 42x optical zoom lens that, through ZoomPlus technology, digitally extends the zoom range to approximately 84x. The camera's lens, which includes three UD lens elements and three aspherical lens elements, makes possible a telephoto zoom range that surpasses that of its predecessor, the PowerShot SX410 IS (released in March 2015).

The SX420 IS incorporates a high-resolution CCD sensor offering approximately 20 million effective pixels that, working in conjunction with Canon's DIGIC 4+ image processor, delivers highly detailed and expressive imaging performance.

With body dimensions of approximately 104.4 mm (w) x 69.1 mm (h) x 85.1 mm (d) and weighing approximately 325 g, the compact, lightweight SX420 IS realizes ease of handling that is further enhanced by its curved grip, which facilitates firm holding performance.