Which is your lens’ sweet spot ?

Most of us, street photographers, knows very well what the Deep Of Field (DoF) is and which aperture will allow us working at the hyperfocal distance.

However, the last digital lenses (specially those designed for CMOS cameras) don’t make this things very clear. For example:

As you can see, the red lines reveal us which aperture we have to use in order to work with Hyperfocal distances. In this Pentax-A 28mm/f2,8, the marks indicates that the Hyperfocal aperture is f8 and that all between ∞ and 1,5m will be acceptable sharp.

But, what is that about «the sweet spot» ?. The sweet spot of a lens means that every lens has a special aperture that will offer you the best image quality. This fact is related to the maximum aperture, and this «special aperture» is in most models between 2 and 4 diaphragms over the maximum aperture. If you have used lenses with f1,4 or higher you may have noticed that at the maximum aperture your lens starts to show some artifacts and colour aberrations. If you want to avoid this kind of unpleasant effects and you are seeking for the highest sharpness with your sensor/lens combination can offer, you should find out which your lenses sweet spot is.