A Diffraction of spherical wave by plane grating

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Diffraction patterns from a plane grating can be analyzed using an ideal focusing lens, where the pattern's size correlates with the lens's focal length. If the incident wave is divergent or convergent, the resulting diffraction pattern will be positioned at a distance larger or smaller than the focal length, respectively. The sharpness of the diffraction pattern may vary depending on whether it is projected onto a plane or a curved surface. The size of the diffraction pattern is believed to remain proportional to the distance d, assuming a perfect lens, but real lenses introduce complications due to aberrations. Understanding these effects is crucial for accurate optical design and analysis.
Philip Koeck
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Textbook examples usually involve a plane monochromatic wave that is diffracted by a plane grating.
If one places an ideal focusing lens behind the grating one will get a diffraction pattern in the back focal plane of the lens.
The geometric size of this diffraction pattern is proportional to the focal length of the lens.

Now if the incident wave is divergent or convergent then the diffraction pattern will end up at a distance d larger or smaller, respectively, than the focal length.

There are two things I'm wondering:

Is the diffraction pattern still sharp on a plane or on a curved surface?
Is the size of the diffraction pattern still proportional to the distance d?
 
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I believe that for a hypothetical perfect lens the pattern will be planar and the distance will scale. Of course there are no perfect finite lenses in practice so we are now into the complicated world of lens abberations...I usually avoid this place.
 
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