Zemax Spot Diagram
Rosalee Ocegueda
I have an application in which I would really like to have access to the raw spot diagram data, both with and without surface scattering. This includes the ray spatial coordinates as well as their direction cosine coordinates. Not sure why it is not available from the analysis window -- seems like a rather basic aspect. In any event, it would be nice if the datagrids were exposed in the ZOS-API.
On a related note, I can certainly trace rays to programmatically create a spot diagram (similar to Example 22), but with IBatchRayTrace, which mimics the old DDE Extensions for sequential batch ray tracing, there is no option to include surface scattering. So, adding a boolean switch for scattering would also be helpful!
What is your wavelength weighting? Spot diagrams are geometric, not diffraction-based, and aren't a good measure of system performance when comparing them to diffraction-based analysis like MTF and EE. You appear to have high SA for rays near the pupul rim, and that can make spots appear much larger. Post up a ray fan plot. I'm guessing it will show relatively low ray spreading across most of the aperture, then large whiptails near the pupil rim. The ray aberrations would be larger, but there's not much energy out there. Trust diffraction MTF and EE more than spots.
This is referring to the angular deviation between a given ray and the chief ray, in image space. In afocal mode, the idea is that the output wavefront is planar (so, the output ray bundle is perfectly collimated). This means that there's ideally zero angular deviation between any two rays in image space. OpticStudio uses the chief ray angle as the (0, 0) reference angular coordinate (regardless of it's image space direction cosines). Then, sampling across the pupil, it checks angle each ray makes with respect to the chief ray, breaking the angle into the X and Y components. If there's any angular deviation in either the X or Y directions with respect to the chief ray, that shows up in the angle-space spot diagram as an offset from (0, 0) in the X/Y direction respectively.
Spot diagrams are a graphical tool used to evaluate the image quality of an optical system. They are commonly used in the field of optics to evaluate the performance of lenses, telescopes, microscopes, and other optical devices.
Spot diagrams are created by tracing a bundle of rays from an object through an optical system and then plotting the position of each ray on a diagram. The diagram typically consists of a grid that represents the image plane of the optical system, and each ray is represented by a point on the grid.
The position of each point on the diagram represents the location where the corresponding ray intersects the image plane. The size and shape of each point represent the size and shape of the spot that would be produced on the image plane by that ray. By analyzing the distribution of spots on the diagram, it is possible to evaluate the image quality of the optical system.
Spot diagrams can be used to evaluate a wide range of optical properties, including chromatic aberration, spherical aberration, coma, astigmatism, and distortion. They are a powerful tool for optimizing optical system design and for identifying and correcting problems in existing systems.
Armed with insights from spot diagram analysis, the optical design team embarked on an iterative optimization process. Adjustments to lens curvatures, thicknesses, and the introduction of corrective elements were made to counteract the identified aberrations. The impact of each adjustment on spot diagrams and RMS wavefront error was meticulously monitored throughout the optimization process.
The outcome of the optimization efforts was a microscopy system that underwent significant improvements. The optimized system exhibited consistently smaller, more uniform spots across the entire field of view. The distortions induced by aberrations were effectively mitigated, resulting in sharper and clearer images of cellular structures. The reduction in RMS wavefront error, as quantified through spot diagram analysis, indicated a substantial enhancement in the overall optical performance of the system.
The significance of this case study lies in the practical importance of spot diagram analysis in addressing complex optical challenges. By leveraging the insights gained from spot diagrams, the researchers achieved a high-resolution microscopy system that not only met but exceeded the stringent demands of their cellular biology studies. This success underscores the critical role of spot diagram analysis in guiding optical system optimization and achieving superior imaging outcomes in the realm of scientific research and applications.
Misunderstanding the influence of diffraction on spot diagrams is also a frequent error. Diffraction places fundamental limits on the achievable spot size based on the aperture size. Expecting diffraction-limited performance in all scenarios, especially for systems with large apertures, is unrealistic. Distinguishing between the effects of diffraction and other aberrations is crucial for setting realistic performance expectations and optimizing systems effectively.
Additionally, some may overlook the impact of wavelength-dependent aberrations. Spot diagrams often consider specific wavelengths, and changes in the refractive index with wavelength can introduce chromatic aberrations. Ignoring wavelength dependencies can lead to incomplete assessments of system performance, particularly in applications sensitive to color fidelity.
Lastly, an error commonly made is assuming that spot diagrams alone provide a comprehensive evaluation of image quality. While spot diagrams offer valuable insights, they represent a simplified two-dimensional representation and may not fully capture the complexities of three-dimensional imaging. Integrating additional metrics, such as modulation transfer functions and encircled energy, provides a more holistic assessment of optical system performance.
In summary, spot diagrams are a graphical tool used to evaluate the image quality of an optical system. They are created by tracing a bundle of rays through an optical system and plotting the position and size of each spot on a diagram. By analyzing the distribution of spots on the diagram, it is possible to evaluate the image quality of the optical system and identify areas for improvement.
I set up a telecentric optical system consisting of multiple lenses. Now after optimizing the system my spot radius appears smaller than the airy disk radius. I would assume the airy disk is the smallest possible spot my system would have when free of any aberrations. How is it then possible for the system to have an image quality even better than the airy radius? Is that an error in my system or does Zemax have a different definition of spot radius/airy radius? Iif you need any more details I will try to provide them. Here is an image of the spot diagram:
The spot radius being displayed here is based only on the geometric rays and doesn't account for the diffraction limited behavior of your system. Since your spot is smaller than the Airy disk, that's one indication that your system is diffraction limited and you will likely instead want to use other analyses such as the PSF to get a more realistic understanding of your system performance.
No problem! FYI, the reason that we have both a geometric spot radius analysis as well as other analyses that consider diffraction (like PSF) is because the geometric calculation is MUCH faster and it's accurate for cases with sufficient aberration. But, as you've illustrated, there are also times when the geometric analysis isn't an accurate reflection of the system because it predicts overly optimistic performance. So if you're not sure whether your system needs to account for diffraction behavior, a general recommendation is to compare the results of the two similar analyses (Spot v. PSF, for example) and if they differ significantly, go forward with the diffraction calculation. We have more examples and guidance on this in the Optical System Design Using OpticStudio course available in OpticsAcademy.
I would like to determine the centre of the mass of the spot and its location coordinates for the outermost field. It is easy for the on-axis rays, the spot is in the centre, IMA, and cursor coordinates show [0, 0]. However, the spot is stretched for the most outer points on the field plane. Do IMA coordinates show the spot's location on the image plane and the centre of the spot mass simultaneously?
The second thing is that when I was trying to find the location of the spot based on the IMA values using the mouse cursor, the IMA and cursor coordinates values were similar ( with the same signs) but the cursor was away from the spot ( situation 1), in situation 2, when I set the cursor in the centre of the spot, the cursor coordinates were opposite to IMA values.
In a Spot Diagram, the IMA label indicates the position of the grid with respect to a reference defined in the settings. If you click on Settings in the top-left corner of the Spot Diagram, you should see something like so:
In that settings window, you have a drop-down menu labelled Refer To and this is what IMA will use to display the different spots. By default, it should be Chief Ray. Meaning the position of the spot is shown relative to the chief ray landing coordinate in the Image Surface. You can also use Centroid to refer the spot diagram to the centroid (centre of mass) of your spot.
Perhaps, another way to look at this is to use a Refer To: Vertex, in that case, the reference for the spot grid is the surface vertex and is likely to be the same for all spots. Have a look at this system:
As you can see, because both spots land on the same surface, the Vertex is the same, and IMA stays at 0.000 mm. One spot (on the left) is in the centre, and the other (on the right) is at the very edge of the grid (towards the top). If I change to Refer To: Chief Ray, this is what the Spot Diagram looks like:
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