Alan shows in his excellent diagrams that a 2x TC cannot improve the resolution of a lens.
But this does not mean it will not increase the resolution in an image. If two points are diffracted, but scattered over more pixels, then the
chances of seeing a dark pixel between the two lighter points is increased.
I've just run a calculation with a nominal 400mm f/5.6 lens and two overlapping Airy disks. The results show that spreading the light over more pixels does improve the resolution, taking the Airy disk radius as 4 microns and a pixel size of 4 microns too which is about that of a 7D2 or 5DS. I hope to show these results once I've persuaded Excel to display them easily.
But this does not mean it will not increase the resolution in an image. If two points are diffracted, but scattered over more pixels, then the
chances of seeing a dark pixel between the two lighter points is increased.
I've just run a calculation with a nominal 400mm f/5.6 lens and two overlapping Airy disks. The results show that spreading the light over more pixels does improve the resolution, taking the Airy disk radius as 4 microns and a pixel size of 4 microns too which is about that of a 7D2 or 5DS. I hope to show these results once I've persuaded Excel to display them easily.
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