My lens has a sweet WHAT?!?

So the discussion came up in my photography class this past weekend about the "sweet spot" of a lens. I guess I take for granted sometimes that aperture and depth of field are photography concepts that take a while to fully understand. It wasn't that long ago that I didn't know my aperture from a hole in the wall (bad pun intended).

An aperture is literally "a hole or an opening through which light travels." Nothing more, nothing less. The amount of light let through the opening in a lens is defined by aperture stops or f/stops. Each f/stop down allows exactly 50% less light to pass through the lens onto the camera film or sensor.

A basic understanding of aperture is required to understand why a lens has a sweet spot. Basically all lenses are different in terms of quality and build but a good rule of thumb is that the sweet spot, or sharpest aperture, of any lens is typically one to two f/stops down from the lens's maximum aperture. This doesn't mean that you can't shoot at the maximum aperture but the image will be noticeably sharper stopped down. The more expensive a lens is, the closer the sweet spot is to its maximum aperture.

Here are some resources on the subject:
B&H Insights
Digital Photography School
Digital Shot