[wim]

This is incorrect.

As we can see from the charts here at PZ and pretty much everywhere else, diffraction hits well before these aperture values.

A good example is the best MFT lens tested here in the zone, the Oly 75mm f1.8: http://www.opticallimits.com/m43/830-oly75f18?start=1

From f5.6 onwards, the resolution is hit by diffraction already.

Keep in mind that the higher the sensor resolution, the sooner it will be hit by diffraction.

 

Please read my entire post again.

 

Diffraction is always at work, because it is a function of the fact that light bends at edges. In the end it is a matter of determining, in combination with lens aperture and sensor limits, what works best. Diffraction only does not limit a lens at F/1 or bigger apertures; limits at larger apertures are always lens limits, i.e., resolution limits caused by lens flaws etc.

 

This whole thing about "diffraction hits at..." is purely based on the way diffraction influences sytem resolution after a lens hits it highest resolution, as it can only go down thereafter.

 

The problem lies with the fact that people tend to use a shortcut way of saying how diffraction influences the final result. it would be better to say that a particular lens reaches it highest resolution, in combination with diffraction effects, at such and such an aperture, and thereafter it cannot resolve any higher lp/mm. However, that is a rather long and roundabout way to do so.

 

Also, the saying that a particular lens is diffraction limited at a specific aperture, or a bunch of apertures, only means that such a lens cannot resolve higher lp/mm only becuase it is so good that it runs into the diffraction limits, which is a physics constraint due to the properties of light, and in such cases not because of lens constraints.

 

And it is logical that the higher the resolution, the sooner diffraction limit are hit. My tables displayed above clearly indicate that. It si a natural phenomenon. Saying that a lens or system hits a sensor diffraction limit only means that teh diffraction limit for a specific aperture is reached, and based on the criteria you use for determining resolution, that si a fixed aperture, based on sensor resolution or nyquist frequency. It does not mean that a system is not good, or that it cannot do better than another system with a smaller "sensor diffraction limit".

 

All of the above can be calculated fairly easily, BTW. If you are interested, I'd suggest to look up Norman Koren's pages here on the internet. he explains things quite well.

 

HTH, kind regards, Wim