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Look at the following table: enter image description here

By spot size I mean if we have a point source for the object, the angular radius of the spot created by the source as viewed in the image plane. My question is is all of the above the 'standard' criterion used for that specific application and if not then what is?

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All of these criteria are more or less the same. I'm not aware that there is one "standard" criterion. More importantly, I think, is that these numbers obtain for ideal conditions, but real systems will suffer from various imperfections and aberrations meaning that the actual resolution and spot size will be degraded. Furthermore, specific applications may call for a different definition altogether.

The spot size or resolution also depends on the geometry. Hence the resolution of the slit geometry is significantly different from that of a circular aperture. If the optical system in question has some kind of aperture stop that is not circular (say, hexagonal or octagonal) then the spot size will not be circular, and the resolution will depend on the arrangement of the spots.

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  • $\begingroup$ Ok let's me rephrase the question slightly then. Let's say on an exam paper you set you asked someone to do all of these things, i.e. find the minimum angle of separation that can be resolved and for a simple lens and microscope to find the size of the 'spot' created at the end. Would you expect the majority of answers to use (respectively) the equations that I have given above? $\endgroup$ Apr 13 '15 at 17:42
  • $\begingroup$ Yes, those are the answers I would expect. $\endgroup$
    – garyp
    Apr 13 '15 at 19:31

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