[Brightcolours]

[quote name='PuxaVida' timestamp='1288619936' post='3881']

I don't agree with you BC... With the same lens to get the same FoV, you need to get closer to the subject. And to get the similar DoF you have to stop down more in FF. But in what extend? As far as I know, the delta between diffraction limited aperture of a FF and cropped sensor (with the same resolution) is more than the aperture increase to get the similar DoF. Maybe I'm wrong but this is how I know it...



Kind regards,



Serkan

[/quote]

Comparing the same lens does not make sense either!



You do not choose an f-value to use as standard between sensor formats. You choose an f-value to get the DOF you want.



Likewise: Focal length.



You choose the focal length to get the field of view you want. You do NOT choose a focal length as standard between sensor formats!



Diffraction is solely aperture based.



F-values are NOT aperture, they are focal length divided by aperture. You will find that when you use EQUIVALENT focal lengths and EQUIVALENT f-values, the aperture will be the same for APS-C and FF.



So what will be the same:

* the field of view

* the aperture

* the DOF

* the diffraction (same aperture)



However, there is one factor in play that can make a small difference: the distance from the aperture to the sensor. Usually, when you use a 50mm lens on APS-C the aperture will be closer to the sensor than with a 85mm lens on full frame camera. The bigger distance actually puts the FF sensor camera in a disadvantage diffraction wise.



But generally speaking, the diffraction effects on the IMAGE for FF and APS-C are similar when you use equivalent f-values and equivalent fields of view.



Note that I am referring to the diffraction effects on the IMAGE, the only sensible way to look at diffraction softening. I am not talking about diffraction softening on pixel level, the nonsensical way of looking at diffraction softening effects. What matters is the image, never the pixel.