Hi,
One thing to keep in mind is that it is not possible to keep everything in focus. There is just a plane of focus, a plane that has some curvature. Going up in resolution reduces the depth of actual focus.
Shooting digital, it is normally accepted that once the Airy circle diameter exceeds twice the pixel pitch resolution is significantly reduced. So going to small pixels we need shoot with large apertures and depth of focus will be short. Just an example:
Let's assume a DSLR with a 50 mm lens and a pixel pitch of 4.8 microns and using the CoC equal twice pixel pith criteria, hyperfocal distance at f/8 will be: 31 m
Now let us go to 2.5 micron pixels, still using the same camera, with a truly excellent lens like the Otus used at f/4 where it tends to have it's best performance the hyperfocal distance will be 125 m.
Now, let's use an 80 mm lens on an MFD with 5.2 micron pitch at f/8, hyperfocal distance will be 80 m.
Shooting that 80 mm lens on 2.5 micron MFD at f/5.6 would give a hyperfocal distance of 226 m
…
This can be quite relevant. In the discussion following Tim Parkins comparison between large format film and MFD, Hans Strand (a well known Swedish landscape photographer) strongly suggested that he doesn't get better results with large format film than with MFD, due to diffraction. It is discussed in this article:
https://www.onlandscape.co.uk/2011/12/camera-test-editors-commentary/See quotes below:
This isn’t quite the end of the story though, as seen in Hans Strand’s comments where he says he is getting better results from his medium format back than he was getting from 5×4 and 8×10. Digging a little deeper, Hans was using much larger apertures that used in the tests so I did a few calculations. The following table might look really confusing at first but bear with me. What I’ve done is to provide, for each platform, a list of aperture’s used in the test where each row shows an equivalent aperture for each platform. i.e. the first row in each table is the aperture that gives the same depth of field for that platform. What follows this is the theoretical maximum enlargement based on diffraction (based on the table here) – however I’ve modified these to limit the maximum enlargement based on a couple of different factors. The first limitation is the maximum enlargement of a 35mm digital ~20Mp camera which is 12″ x 18″ (at 300dpi). The next limitation is placed on the Phase IQ180 system because it has a maximum enlargement of 26″ x 32″ (based on 300dpi). The next limitation the maximum resolution for lenses for the Mamiya 7 which is about 100 line pairs per mm. The final limitation is the resolution of LF lenses which is about 70 line pairs per mm. Each of these tables now shows the largest enlargement in mm for each platform and each f-stop for equivalent depth of fields. Fortunately you can ignore all of that maths and skip your way down to the very last table which shows the ratio of the different platforms to each other at equivalent focal lengths.
In summary, this table shows the maximum critical enlargement for each camera type at each aperture taking into account diffraction and ‘best lenses’. e.g. 35mm and Mamiya 7 are film limited at 13x but the IQ180 sensor will allow a 19x enlargement before diffraction kicks in. The last table shows the relative enlargement ratios of the camera pairs shown. e.g comparing IQ180 and 8×10 shows that at smaller apertures the advantage to 8×10 is 2.3x but this falls behind at f/90 to 0.9x – diffraction has killed 8×10’s advantage
I am pretty sure that this always applies, weather shooting small sensor or large format film. To get DoF we need to stop down and that limits resolution. Two exceptions landscape with no significant foreground and tilted plane of focus.
Focus stacking is a way around the problem, but has issues with anything that moves.
Best regards
Erik
