Methods
Software
The process for analysis was done through several software programs. First the lens systems were designed in Zemax. Zemax created the vast amounts of lens data and raytrace data that ISET would use. ISET would then allow for futher analysis of these images as well as produce simulated optical images from the raytrace information. This is very detailed information that results from individual point analysis. Finally once the data was accessable through ISET I was able to start futher analysis. ISET made it easy to access the data.
Zemax
Zemax is an optic system design software that is available commercially. Other optic system design software that is commonly used (and used by the Rim et al paper) is CodeV. There are distinct difference in data analysis between Zemax and CodeV as I found out during the process of this project.
For this project Zemax lens analysis was limited to a single wavelength (550nm). Most of the ray trace angles were limited to three defining locations: 0 deg, 11 deg, 26 deg, and for ball_cfpa 34 deg.
ISET
Image System Evaluation Tools (ISET) is a 3rd party toolbox add-on to Matlab from the company ImagEval. This toolbox contained functions that would automatically convert the data from lens designs in Zemax and convert them into accessable variables in Matlab.
ISET allows for creating a scene to analyze. This scene has photon components and for the purposes of this project the only wavelengths used were 400nm, 500nm 600nm. By limiting the wavelengths of the image the ultimate optical image simulation finish quicker.
The ISET-optics would be able to then convert and import the Zemax data. The optics analysis required an additional module in ISET called RayTrace. Using raytrace the optics data was analyzed (see Results).
In addition, it allows for the use of point spread function and apply them to a simulated sensor plane image. It is important to note that for much of the simulations results were displayed within a reasonable amount of time, for full optical image simulations using raytrace information each pixel was analyzed individually and so for a 128x128px (smallest) optical image size it took minimum 35min, for a 256x256px image it normally took 2.5 hrs. As a result only a limited number trials as well as limited resolution for scene and optical image analysis were available.
Lens type used
The following are the description and details of the three lens systems used during the analysis of this project. The three types were chosen based on the common use and applications. Each lens in the context of this study were used as imaging lenses.
Plano-convex PCX
1-element plano-convex lens on a planar FPA. Plano-convex refers to the lens element which has one side positive spherical lens and the other side a flat (plano) side. This is one of the most commonly used lenses. Notice that the rays do not focus on the FPA beyond the center of FPA. This issue of ray spreading effects data collection in all the lens parameters. Therefore the analysis of the PCX lens could not be compared in as much detail as the other lenses were. Suffice to say that the lens properties of the PCX model is so poor that no analysis is nessesary to show its sub-par imaging qualities.
Digital Camera
3-element simplified digital camera lens design with a planar FPA. This is a simplified model, more complex and expensive optical systems with more elements may have better properties. Notice the ray is focused on the FPA at all times unlike the PCX lens.
Ball CFPA
1-element spherical lens (ball) with a curved focal plane array (CFPA). While the image may appear to be a 2 element lens system it is actually one. The aperture needed to be defined in the center between the two sides of the single lens. Both lens have the same radius and thus if extended to their full diameter would look like a circle. The CFPA is spherical sharing the same center as the lens at the aperture location. Later in this report we will discuss the effects of misasligning the curvature (Geometric Robustness)
Glass type specified as: BK7, a standard optical glass component.
