Nikon L21 has a 8.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor and features Expeed C2 processor. You can shoot at maximum resolution of 3648 x 2736 pixels with aspect ratios of 4:3 and 16:9. L21 has a native ISO range of 64 - 1600 but unfortunately, Nikon L21 doesn't have RAW file support. If you need a Compact camera with a RAW support, consider or in the same price range.
Nikon L21 is not the highest resolution Small Sensor camera. Canon SX740 HS with its 21.0MP sensor is leading in this class. Check the comparison of Nikon L21 vs Canon SX740 HS or take a look at Highest resolution Compact cameras list.
Let's look at how the size of the Nikon L21's 1/2.3-inch sensor compares with other standard sensor sizes.
Comparison image of Nikon L21 Sensor Size with other standard sensors
Sensor size is what determines the circle of confusion, and therefore how much
depth of field Nikon L21 gives you at any given aperture.
You can
calculate
the exact depth of field for the Nikon L21
at any focal length, aperture and subject distance, including the hyperfocal distance
for landscapes and how close you can get before the focus zone becomes too thin.