# Design of Zoom Optical System from Visible to NIR-II for Vivo Fluorescence Imaging Device
## 3 Optical Design and Optimization
### Optical System Optimization  
Afterward, we checked the Ray fans diagram to determine the aberration, in which we saw that the off-axis aberration was larger, indicating that the design could be as close to the symmetric layout as possible. The initial optimization resulted in a few more stable optical system layouts, and the subsequent design was based on the best of these layouts.  
Considering the processing problem, the lens cannot be too thick, as this will make the optical system weight increase, and part of the glass material cannot be too thick; the lens edge cannot be too thin because it is easy to cause a collapsing phenomenon in the assembly. The spacing between the lenses also needs to be controlled. In this paper, the air spacing between the lenses is set greater than 0.2 mm, and the minimum spacing between the components is greater than 1 mm. The system requires a back intercept distance greater than 17.526 mm due to the adaptation of the C-mount. These requirements can be controlled by TTHI, OPGT, MNCA, MENA, etc.  
After meeting these requirements, the system aberration needs to be further optimized by analyzing the main aberrations of the optical system through the spot diagram and the Ray fans diagram, viewing the distribution of aberrations by the Seder diagram, and appropriately changing the parameters of the surface with a large contribution to the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group** & **1** & **2** & **3** & **4** \\ \hline Initial EFL/mm & 117.64 & \(-\)70.14 & 42.87 & \(-\)140.34 \\ Final EFL/mm & 124.385 & \(-\)78.783 & 42.717 & \(-\)182.017 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Focal length of the four groups.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Distance** & **d\({}_{12}\)** & **d\({}_{23}\)** & **d\({}_{34}\)** & **d\({}_{4f}\)** \\ \hline Short focal length/mm & 0.2 & 80.15 & 4.71 & 17.526 \\ Long focal length/mm & 65.47 & 15.175 & 12.883 & 27.116 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Spacing between each group in the initial layout.  
aberration. In the optimization process, we found that chromatic and spherical aberrations are the most important aberrations. The source of chromatic aberration is generally caused by the different refractive indices of the lens materials in different wavelengths of light. The correction of chromatic aberration can be combined in the ways mentioned above--the combinations of the positive and negative lens, combinations of different dispersion material lenses, double-glued lenses, or even triple-glued lenses. Using several material combinations above, three sets of double-glued lenses were used to decrease the aberration to an acceptable level. The main methods for correcting spherical aberration are glued lenses and the separation of optical focal lengths, both of which were used. We split the lens that bears a larger optical focal length into two lenses. If the image quality does not meet the requirements, you can also add the operand MTFA control center field of view, MTFT; the MTFS control edge field of view can be further optimized, and distortion can be used in the DIMX operand for control. After fine-tuning and multiple optimizations, it was found that the image quality of each focal length could meet the requirements and reach the design index.