OK, I've read the article...
http://luminous-landscape.com/tutorials/resolution.shtmlIt's a very technical article - some of which I understand, some I have a rough understanding and the rest is over my head! I need a little bit of help to try and understand diffraction has an impact on IQ and how this has a relavence to lens choice for Landscape shooting.
So to quote:
You have all the data at hand, but take the green-yellow light and f/8-f/11 aperture values as a reference. It represents a realistic, not too demanding case. Consider a 35mm system with a lens at f/11. At best, the maximum resolution you will get is equivalent to 16 MP, even if your camera has 22 or 25 MP. In the case of an APS-C based system the limit goes to 7 MP, and 4 MP considering a Four Thirds format. Stopping down to f/22 the limit of the effective resolution of the 35mm based system goes to 4 MP!There are a lot of factors (too much to go into), but the bottom line seems to be that the larger the sensor the less 'diffraction' occurs in reliative terms.
So from the above quote, at f11, the most MP you can get out of APS-C is 7MP and FF 16MP. And by the time you hit f22 you are down to 4MP on FF. And then it continues....
See again the Figure 2: the lens limits the resolution of the 5 microns pixel based system with an aperture of f/22, but it is also the case for f/16, f/11 or even f/8. That pixel pitch leads to a 10 MP Four Thirds sensor, a 15 APS-C sensor, a 35 MP sensor of 35mm format and a 70 MP sensor of 36x48mm dimension. Compare now those numbers with the values presented in Table 3. Only for highly corrected lenses (with better performance at f/5.6 than f/8) do higher sensor resolutions make sense. For instance, you can put 60 million of pixels into a 35mm sensor, but only a diffraction-limited lens at f/5.6 would take advantage of it. The price to pay is in the form of huge files, and comparatively low signal to noise ratios (which translates to noise, narrower dynamic range, poorer tonal variability… see, for instance, the Olympus E-3 reviews at dpreview.com and at The Luminous Landscape). The only alternative way for more detail is more capture surface, this is, a larger format, but aberrations are harder to control for larger light circles (see the “Y” variable in this table).Q1
When we are comparing the impact sensor size when shooting at small apertures for Landscapes, we are choosing small apertures for increased DOF (and maybe other factors, but lets leave this out for now). I assume we also need to take into account that the smaller the sensor the more DOF you'll get for the same aperture (1 stop difference between APS-C and FF at a guess? Please correct if this is wrong!) meaning that any gains made from a larger sensor are somewhat impacted by the reduced DOF on the larger sensor, meaning that you would need to use a smaller aperture for the same DOF on FF compared to APS-C
Q2
What I am really trying to understand, is at the point of which diffraction is limiting resolution what difference does the lens quality have at this point. i.e. if I was shooting with a 24-70 lens attached to say a D3x shooting at f16 or even f22 (where diffraction is limiting resolution regardless of the lens choice), would there be much difference in IQ between a £300 3rd party lens verses a £1200 Nikon, Canon or Sony? And if so, could someone expand on what impact the lens quality has at this point. I'm trying to work out at the point at where lens diffraction is limiting resolution, whether the lens MTF figures have a major impact on the resulting IQ.
I hope what I'm asking makes sense. If not, I'll try again and try and explain what I'm wanting to know.
