Aperture-aware lens design

Abstract

Optics designers use simulation tools to assist them in designing lenses for various applications. Commercial tools rely on finite differencing and sampling methods to perform gradient-based optimization of lens design objectives. Recently, differentiable rendering techniques have enabled more efficient gradient calculation of these objectives. However, these techniques are unable to optimize for light throughput, often an important metric for many applications.

We develop a method for calculating the gradients of optical systems with respect to both focus and light throughput. We formulate lens performance as an integral loss over a dynamic domain, which allows for the use of differentiable rendering techniques to calculate the required gradients. We also develop a ray tracer specifically designed for refractive lenses and derive formulas for calculating gradients that simultaneously optimize for focus and light throughput. Explicitly optimizing for light throughput produces lenses that outperform traditional optimized lenses that tend to prioritize for only focus. To evaluate our lens designs, we simulate various applications where our lenses: (1) improve imaging performance in low-light environments, (2) reduce motion blur for high-speed photography, and (3) minimize vignetting for large-format sensors.

Aperture-aware gradients

gradcheck — We consider an image of the SIGGRAPH logo through a lens, and differentiate it with respect to two lens parameters: (top row) aperture size, and (bottom row) curvature of the first refractive element. We compare the gradient images from: (a) our method, (b) finite differencing, and (c) DiffOptics [Wang et al. 2022]. Our method produces accurate gradients with respect to both lens parameters, and its results match those from finite differencing. By contrast, the biased gradients from DiffOptics cannot account for aperture size changes, producing a gradient image that is identically zero.

Throughput-sharpness trade-off

thrusharpfront — We use our warp-field technique to optimize the same initial design using the composite objective of throughput and sharpness with varying weights λ. The left plot quantifies the throughput and spot-size performance of the resulting set of lens designs, as well as designs optimized with DiffOptics[Wang et al. 2022] and Zemax. By using unbiased gradients, our technique produces lens designs with better throughput at comparable spot sizes as DiffOptics and Zemax, which both use biased gradients. Our technique additionally produces multiple other designs that achieve different trade-offs between throughput and spot size. The right figures show the lens configurations, spot diagrams, and simulated images of USAF resolution targets for the designs corresponding to the lowest (first row) and highest (second row) λ values, DiffOptics (third row) and Zemax (fourth row). These figures help qualitatively assess the differences in spot size and throughput performance. For example, the spot-size-focused design in the first row has a smaller spot, but also transmits fewer rays than the throughput-focused design in the second row.

Low-light scenes

In low-light scenarios, optimizing for more sharpness in a lens may not yield better results in the presence of noise. Alternatively, optimizing for throughput can capture more light from the scene at the cost of some sharpness

Resources

Paper: Our paper is available here.

Code: Our code will be available soon.

Citation

@InProceedings{Teh2024ApertureAware,
	author    = {Teh, Arjun and Gkioulekas, Ioannis and O'Toole, Matthew},
	title     = {Aperture-Aware Lens Design},
	booktitle = {Siggraph},
	month     = {July},
	year      = {2024},
}

Acknowledgments

We thank Yexin Hu for providing code for importing Zemax files to Blender, and Maysam Chamanzar for facilitating access to a Zemax license. This work was supported by the National Science Foundation under awards 1730147, 1900849, and 2238485, a Sloan Research Fellowship, and a gift from Google Research.