TravisAllen747

Introduction

For my course project, I wanted to learn more about the Image Systems Evaluation Toolbox (ISET) while incorporating some of my experience with optics and an optical design program known as Zemax OpticStudio. Several years ago (potentially 10-12 years ago), others had developed a basic capability for bringing lens parameters, as defined in Zemax, into ISET for use as "raytrace optics". The current implementation is pretty straightforward, but it is a bit dated. When this method was originally implemented, there was no inherent interoperability between Opticstudio and Matlab (the programming software that runs ISET). Now, in 2017, OpticStudio has options for interfacing with several external programs, including Matlab.

Since I was working alone and fairly unfamiliar with both ISET and the current method for interfacing with Opticstudio, my project began with the primary goal of taking a lens system in Zemax Opticstudio and importing it into ISET using the old method. Since the scripts that did this had not been used by anyone in quite some time, my plan was to work through each part of the process and fix anything that didn't work and clean up code that was unnecessary. My hope was to learn more about both ISET and Zemax OpticStudio along the way.

The second (stretch) goal was to try and modify the way the PSF's are currently applied in the raytrace optics chain in ISET. Currently, the PSF values are interpolated between field heights and wavelengths. A potentially better method, as described by Professor Wandell, would be to parameterize the PSF's as Gaussians and interpolate between those defining parameters (like variance). Unfortunately, I spent quite a bit of time on the first goal and was unable to make any meaningful progress on this second goal.

Background

In the Image Systems Evaluation Toolbox (ISET) in Matlab, one can simulate each part of an image capture chain: from the scene, to the optics, to the sensor, to the processor, and, finally, to the display. This project focused on the "optics" portion of that chain, which essentially transforms the scene radiance to the optical irradiance, which can then be captured by the simulated sensor. One lesser used method in ISET for describing and implementing this optics transformation system is called the "raytrace" method. The raytrace optics scripts and methods in ISET tend to revolve around output from Zemax Opticstudio, optical systems design software that is widely used in the industry. Since these scripts are rarely used, some of the code has become outdated and needed to be cleaned up.

The main file that needed to be updated was the Zemax Opticstudio export macro. When the capability to import raytrace lens parameters from a program like OpticStudio was originally conceived, there was no straightforward method for exporting parameters into external programs (like Matlab) for manipulation. However, Zemax did allow for macro programming in order to rapidly execute tasks. So, about 10 years ago, the ISET team wrote a macro that went in, executed several commands, and exported data in a well-defined format. This macro is written in the .ZPL format which, when run, will output wavelength and field height-dependent Point Spread Functions (PSF's), relative illumination, and distortion parameters for the optics system currently loaded in OpticStudio. This macro had a lot of obsolete keywords that needed to be updated and a few parts that needed to be modified to work with more general lens files.

On the ISET side, there are a series of scripts that need to be implemented to import the data from the files created by the macro into a usable format in Matlab. There were several files that needed to be updated to ensure that the data was transferred into ISET in a correct manner.

Methods / Updates Made

Zemax OpticStudio Export Macro

The import macro I focused on for this project was the ISET_RT_ZEMAX_2D.ZPL macro. There is a 3D version, but, since I am uncertain as to whether or not it is currently implemented in ISET, I focused on the 2D file. Throughout the macro, there were obsolete keywords and formatting issues that needed to be addressed. I made these changes and added comments throughout in order to document them. There was also an issue with an initial RAYTRACE command that appeared to rely on the original lens file to have a few different field heights available by default (which is not always the case). Additionally, since ISET is expecting FFT PSF output, and the macro had been changed to output a Huygen PSF, I changed it back to the expected format. ISET import scripts are literally hard-coded to read the FFT PSF file format in the current implementation. I also added back into the script the ability to output grid distortions, which had been part of an early version of the macro but was removed at one point. I commented out this portion of the script because it does not appear to be used currently in ISET, but these files may be useful at a later date and I wanted to capture that.

Figure 1: Where to Place the Macro

ISET_RT_ZEMAX_2D.ZPL has now been fully updated to work with Zemax OpticStudio 17.5 and should execute correctly when placed in the Zemax/Macros folder. See Figure 1 for an illustration of where to put this file.

Figure 2: How to Run the Macro (Step 1 of 2)

Figure 3: How to Run the Macro (Step 2 of 2)

It's fairly simple and straightforward to run the macro. Once you have made the basic changes to the macro itself (identifying how many wavelengths and field heights you want, for instance), you then go into Zemax OpticStudio and run the script using the commands as illustrated in Figures 2 and 3.

Figure 4: Example of the Macro Running

When you execute the macro, you should see a window pop up with a bunch of output as can be seen in Figure 4.

Figure 5: Location of the Exported Files

Once the macro is finished running, the exported files will reside in a directory inside of Zemax/Samples. This directory is created based on the name of the lens (here AB0618MG).

One Note: while the macro is capable of creating this directory on its own, it will NOT create the ISETPARMS.txt file that it needs to write to within this directory. For that reason, it makes sense to create the directory and place a blank .txt file in it with the name ISETPARMS.txt. Then there should be no errors.

Appendix

You can write math equations as follows: $y=x+5$

You can include images as follows (you will need to upload the image first using the toolbox on the left bar.):