Resolution vs. Diffraction

As the Nikon D800 came out, many argued that the many pixels are useless, some even think they hurt image quality because of diffraction.

 

Simply put: Yes diffraction exists, but having more pixels still give you an edge.

 

So how did I find out: In the image above the right column has been shot at 70mm and the indicated aperture. I shot with a D90 where diffraction starts to become clearly visible from f/11 on.

The left column had been shot at 120mm with an aperture 1.3 stops smaller to imitate the diffraction of smaller pixels. Distance stayed the same, I cropped the same region and exported from Lr4 with standard screen sharpening to a resolution of 1200x800, which involved up-scaling for the right column (here the same without upresing ).

 

Why these numbers: The idea was to use only a third of the pixels, which means a 1.7 crop factor. 70mm * 1.7 = 120mm. The 1.3 stop difference should be 1.26, but this cannot be set on any lens - the difference is small and leans to more diffraction. (1.26 is the base 2 logarithm of 1.7). Thus the left series had been shot at f/9, f/13 and f/18.

 

When you browse the columns, you can see the effect of diffraction, the topmost images contain more detail. Comparing side by side shows that the additional resolution really helps the image.

 

So will I get a D800? Not decided yet, but I am not worried about the high resolution.

 

You can see the difference yourself in 100% view

 

You might also want to see the experiment on noise-downsampling

Done