[Brightcolours]

Thank you Klaus for the excellent article.

 

Clear and detailed enough for any practical use.

 

My comment and question is, what you and the community think about "equivalence of DOF" when the final target is to get the maximum depth of field? e.g. for landscape?

 

How do the different systems compare here? What about sensor size and diffraction?

 

Any thoughts with practical relevance :-)

 

Thank you and kind regards

 

Andreas

Lets disregard diffraction softening on pixel level, because it is not part of equivalence.

Diffraction happens inside the lens, light "bends" around the edges of the aperture (simplistic way to tell it). 

 

Light ends up on a different place than it without diffraction would, which causes the softening.

 

Lets get an example.

 

MFT, 50mm f4 lens. 

FF, equivalent lens : 100mm f8. 

 

Both lenses will give a similar DOF. Both lenses have a similar aperture size:

50mm / 4 = 12.5mm, 100mm / 8 = 12.5mm.

 

The apertures are the same, so light gets diffracted around their edges in a similar fashion.

However, the aperture of the 100mm lens probably sits quite a bit further away from the film/sensor, which will mean that the impact of the diffraction on projected image of the f4 lens is less than that of the f8 lens ( extra the distance makes the diffracted light affect a larger area).

So, the MFT lens has less diffraction.

 

The MFT image capture device (sensor) is smaller, though. To get the same size image, we enlarge the image more than we do with the FF image.  The MFT diffraction softening impact gets magnified. 

 

The end effect: For both images, taken with equivalent settings, the diffraction softening impact is similar.