Why Is a Fast Lens a High Resolution Lens?

Because high-ISO noise robs your images of resolution, that’s why. It’s also the reason that a high-resolution sensor does not necessarily yield a better image than one with less resolution but more sensitivity.

A faster lens means shooting with a lower ISO, and a lower ISO means less noise. Noise robs your images of resolution, just as a lower resolution sensor does. Only noise is not really part of the image, and can degrade an otherwise acceptable image very quickly.

So, if your camera uses interchangeable lenses, before you go hunting for a camera with a higher resolution sensor, consider purchasing a faster prime lens. Not only will your images have less noise, but they’ll be sharper as well, as dollar for dollar, prime lenses typically have higher resolving power and less chromatic aberration. Plus, their compact size and reduced weight make them much more portable.

Wide lenses are ideal candidates, as their enormous depth of field make focusing a snap, and if you need a tighter shot you can always crop the image in post. Because the images will contain less noise, they will also enlarge much better.