More Mega Pixels (A bit more)

In a previous Blog I touched on the subject of why I stuck with my 12 mega pixel Nikon D700, in this one I am going to explain it in a little bit more depth.

It all has a great deal to do with a little thing called an Airy Disk, discovered by one George Airy, it is the 2-d diffraction pattern of a wave of light passing through an aperture. There are some calculations for working this out but I am not going to touch on that here as it would go over most peoples heads.

For a given circular aperture there is a set Airy disk diameter, f1.4 that diameter is 1.9 microns and if we go all the way to my favourite aperture f22 has an Airy Disk diameter of 29.3 microns, these figures are based on the wavelength of the middle of the visible spectrum of light. In other words the smaller the aperture the bigger the Airy Disk (confused yet?).

Right that is the first par, next we come on to sensor pixel size. My 12 mega pixel sensor has an individual pixel size of 8.5 microns, if we also look at say the Nikon D810 with a 36 mega pixel sensor each pixel is 4.9 microns (still with me).

Next part. Based on viewing on a computer at 100% the 12 mp sensor has a circle of confusion of 21.21 microns and the 36 mp sensor is 12.25 microns. Now the diffraction limit is said to come in when the Airy Disk diameter is between 2-3 times the pixel size. Roughly the circle of confusion.

As you can see at f22 i am just over the diffraction limit of my sensor ( diffraction starts to appear at f16 based on these figures) and the D810 is a long way over its diffraction limit (Diffraction starts at f8).

Now lots of things can effect what is happening with regards to diffraction limits, light wavelengths and if you are printing the print size and veiwing distance also come into the calculations of the circle of confusion.

My theory has always been. If you start with better quality images then it is far easier to work with them. Diffraction really shows itself as a slight softening of an image and more beyond the limits of your sensor you push it the softer it becomes.

Meadow Grasshopper Nikon D700 Nikkor 200mm f4 micro 1/100 @ f22

© Ian Hutchinson 2017