These file formats, STEP, IGS, SAT, and STL, are commonly used in 3D modeling, CAD, and engineering applications. The main difference between STEP, IGS, SAT, and STL lies in how they store and represent 3D geometry in CAD, engineering, and 3D printing applications.
Zemax OpticStudio, the performance of STEP, IGES, SAT, and STL files can vary significantly depending on the file type and use case, such as non-sequential ray tracing, mechanical housing, or optical components.
The STEP performs fastest among CAD file types because it represents solid models efficiently. Zemax can directly read and convert solids, avoiding excessive triangulation. It can handle complex geometries with high accuracy while maintaining manageable computation time. Furthermore, STEP keeps smaller file sizes compared to STL for complex shapes. It is best for importing mechanical parts, lenses, and optical mounts with precision.
The SAT is comparable to STEP, but partially depends on the software generating the file. Uses the ACIS kernel, which Zemax can interpret efficiently. It handles solid models well, making it a viable alternative to STEP. However, it sometimes appears compatibility issues with non-ACIS-based software. In this case, SAT file is best for importing solid objects when working with ACIS-based CAD systems.
The IGES performs slower than STEP because IGES stores geometry as surfaces, which can lead to gaps and inconsistencies in solid modeling. In Zemax, the IGES may struggle with surface mismatches, requiring extra processing to fix, also leading to higher computation time for ray tracing. While it is less accurate for solid models compared to STEP, the best application scenario locates at surface-based geometry, not recommended for solids unless necessary.
STL is widely used for freeform surfaces and organic geometries that may be difficult to define in traditional CAD formats like STEP or IGES. Furthermore, Good for modeling non-standard optical surfaces or diffusers, scattering objects, and mechanical housings.
Here is a comparison in a Zemax model in Nonsequential mode. An off-axis parabola mirror (highlighted orange) in the layout to reflect and focus an infinite parallel beam (in blue). The reflected beam (in green) focuses light on a distant detector. All focus positions are precisely located by merit function, with distance limited by operands NPZL and NPZG.
The layouts of focal status of STEP, IGES, SAT and STL are listed below. With STEP model, the focal distance is 1983.29 mm, the RMS spot radius at the image plane is 2.82 mm. In this model, the IGES and SAT optical performance is identical as STEP file. If the reflector is imported with STL, the RMS spot radius is 22.16 mm. While the focal distance is identical to what is produced by STEP, the STL presents a bigger focal spot than STEP does.
Optical layout with reflector in .STEP file
Optical layout with reflector in .STL file
Here we do more research between STEP and STL. An STL file always represents surface topography as a collection of triangles. This is because STL is a mesh-based format that does not store exact mathematical surfaces, but rather an approximate representation using a triangular faceted structure.
There are good features in STL over STEP in Zemax, as STL is easy for file conversion between mechanical and optical software in complex geometries, especially some additional specific scenarios where STL has advantages over STEP.
First, STL is better for freeform and irregular shapes because it allows for complex, organic, or freeform geometries that may be difficult to represent with STEP. Useful for light diffusers, micro-optic structures, and rough optical surfaces.
Second, STL output smaller file size for simple mechanical parts. This is when simple mechanical components exist, such as housings, frames, baffles, STL can sometimes be lighter than STEP, especially when solids are not required.
Third, STL works well for non-sequential ray tracing. Zemax can use STL files to represent scatter models, such as rough, textured, or faceted optical surfaces. This is useful for simulations involving diffuse reflection, scattering lenses, or complex surface roughness effects.
Fourth, if importing a 3D scan of a physical object, STL is the preferred format since scans are typically converted into triangular meshes rather than solid CAD bodies.
For high-precision optical simulations, STEP is still the better choice. But STL has advantages in cases where triangular meshes, 3D scans, or scatter models are needed.
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