OpticStudio has a number of operands that allow you to optimize for MTF based on diffraction MTF, geometrical MTF (which is faster, but less accurate than the diffraction MTF) or Moore-Elliot Contrast optimization (a more robust method for optimizing for MTF without using the MTF operands). Methods for analyzing MTF in OpticStudio has a more in-depth comparison of the different methods. These are very powerful tools that allow you to design specifically to your goals. However, early in the design process, the large aberrations make it impossible to accurately calculate the MTF. It is generally better to optimize initially to another criterion, such as RMS spot size, and then to introduce your MTF goal as you approach your final design. MTF calculations, especially when diffraction based, are also not well suited to the early stages of the design process becasuse their execution speeds are much slower than those for the RMS analyses. If your system is not close to the diffraction limit, then the results of geometric calculations will be comparable to the more accurate diffraction calculations, and can be used to expedite your analysis. For a tutorial on contrast optimization, read the knowledge base article Optimizing for MTF performance using Contrast Optimization.