Quote Originally Posted by ic-racer View Post
You can't 'design' a lens to have any specific diffraction characteristic. It a physical function of aperture size. Its simple, the smaller the aperture, the more the diffraction (or the larger the bullseyes). Its physics of light, not design of the lens.
As aperture is relative to focal length it goes without saying that an LF lens at f22 is quite different to a an equivalent 35mm or 120 lens of the same field of view at the same aperture. Diffraction is more apparent with lenses of smaller formats and manufacturers of LF lenses take this into account when designing their lenses, it's not a co-incidence that virtually all of them state the optimum aperture is f22 for their LF lenses.

As you say it's simple but the diameter of an aperture of f22 on a 35mm camera is more likely to be equivalent of f45 or even f64 with an LF lens, and f90 or f128 with ULF lenses, hence the reason f22 is used for best overall balance with 5x4 lenses.

Ian