Resolution when not diffraction limited

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Discussion Overview

The discussion revolves around determining the resolution of optical systems that are not diffraction limited. Participants explore various methods and considerations for assessing resolution in conventional optics setups, including the use of spot diagrams and comparisons with ideal systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants inquire about methods to determine resolution in non-diffraction limited systems, specifically referencing the Rayleigh criterion.
  • Spot diagrams are suggested as a potential tool for evaluating resolution, with a focus on comparing blur diameters between actual and ideal systems.
  • Near-field imaging systems, such as NSOM, are mentioned as examples where resolution is defined by the size of the fiber tip rather than diffraction limits.
  • Participants express uncertainty about the resolution limits of techniques like stimulated emission depletion and other super-resolution methods.
  • One participant emphasizes the complexity of determining resolution in systems with imperfections, noting factors such as spot size, intensity distribution, and symmetry.
  • There is a discussion about the ambiguity of the term 'resolution' and the various characteristics that can be computed, including spot size and modulation transfer function.
  • It is suggested that direct measurement of system performance may be more reliable than theoretical modeling.

Areas of Agreement / Disagreement

Participants express differing views on the methods for determining resolution in non-diffraction limited systems, and there is no consensus on a definitive approach or resolution limit.

Contextual Notes

Participants note that the definition of resolution can vary and that calculations may be complicated by factors such as aberrations, noise, and system characteristics.

Emperor42
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Does anyone know if there is a way to determine the resolution of an optics system that is NOT diffraction limited. I know you can calculate the resolution of a diffraction limited system using the Rayleigh criterion, but that assumes the system is diffraction limited. Is there some way using the spot diagrams?
 
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Emperor42 said:
Is there some way using the spot diagrams?

well, can you give some details of spot diagrams?
 
You could try comparing the spot diagram of the optical system with that of a perfect system. Try comparing the smallest blur diameter for both systems.
 
large FOV.jpg

drvrm said:
well, can you give some details of spot diagrams?
 
Emperor42 said:
Does anyone know if there is a way to determine the resolution of an optics system that is NOT diffraction limited.

You have to be more specific.

Near-field imaging systems are not diffraction limited; in NSOM (near field scanning optical microscopy) the resolution is given by the size of the fiber tip. Stimulated emission depletion is also not diffraction-limited, but I'm not sure what the resolution limit is. Other super-resolution techniques involve multiple images and/or computation.
 
Andy Resnick said:
You have to be more specific.

Near-field imaging systems are not diffraction limited; in NSOM (near field scanning optical microscopy) the resolution is given by the size of the fiber tip. Stimulated emission depletion is also not diffraction-limited, but I'm not sure what the resolution limit is. Other super-resolution techniques involve multiple images and/or computation.

I think I was not being specific in my question. I am using a conventional optics setup with an object, objective lens and a CCD chip. My question is if the optics system is not perfect so light lies outside the airy disk then what is the resolution then?
 
Last edited:
Emperor42 said:
I think I was not being specific in my question. I am using a conventional optics setup with an object, objective lens and a CCD chip. My question is if the optics system is not perfect so light lies outside the air disk then what is the resolution then?

I doubt there's an easy answer. You'd have to evaluate the optical system and the resulting spot diagrams and then do a complicated analysis. Not only does the size of the spot matter, but so does the intensity of the light at different points on the spot, the shape of the spot, and whether the spot is symmetrical or not. I can't say I'm an expert, but I've read a little on this subject, including a book full of spot diagrams of various telescopes and an actual discussion and analysis of resolution in several different contexts. The understanding I came away with was that resolution is complicated to figure out, especially when you have imperfect optics with large, asymmetric aberrations.
 
Emperor42 said:
I think I was not being specific in my question. I am using a conventional optics setup with an object, objective lens and a CCD chip. My question is if the optics system is not perfect so light lies outside the air disk then what is the resolution then?

Not sure what you mean by 'air disk'. Presumably you mean "airy disk"?

In any case, the word 'resolution' is generally poorly defined. You can compute various system characteristics (spot size, cutoff frequency, etc) and these can vary over the image field. In some cases, there is a simple way to compute the modulation transfer function (or contrast transfer function, for sampled systems such as a CCD), but the more fidelity you try to add (Bayer filter, chromatic aberrations, system noise, etc) the more complex the calculation.

If you have a spot diagram, you can try to compute the two-point separation distance (Rayleigh criterion); just be aware that the calculation is not particularly accurate. In general, it's best to directly measure the system performance rather than try to model it.
 

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