F11 Sweetspot?

[PlatinumWeaver]

Quite often when looking at reviews of lenses I will see mentioned that setting an aperture of F11 will give the best results with this lens or that lens.

Can anyone explain why this is?

[nodabs]

well most lenses don't work there best at there extreme's wether this is aperture or zoom so for instance a 70-300 zoom will be it's weakest in terms or sharpness particularly at 300mm and wide open(it's largest apeture) stopping down or reduceing the apeture is a good way of increasing the sharpness of the lense because you increae the tollerances of the lense there is a bunch of physics behind that that i don't understand enough to explain but basically by stopping down and incresing the DOF and decreasing the sensitivity of the lense you are able to (with the approriate shutter speed and/or stable platform) get a sharper photo

[Onyx]

Also, diffraction. On DX sized sensor, it theoretically kicks in at around f/16 (one stop down from f/11).