Folded Fisheye Lens Design for Compact 360-Degree Virtual Reality Camera

Abstract

The consumer electronic industry has continued to drive modern camera design to be as small and compact as possible, as is seen with the rise of very thin smartphone cameras, compact action cameras, and wearable technologies. As sensor technology continues to develop, and consumers prefer more minimal form factors, modern imaging modules are continuously being pushed to be short in length, while maintaining sharp image quality at a low cost. With this, consumers have begun to develop interests in immersive digital content, which has given rise to the popularity of action cameras and virtual reality capture devices, generating high-demand for high performance compact fisheye lens modules. Many virtual reality cameras which are being developed today utilize two fisheye lens imaging modules to create two hemispherical images, which are stitched together to create a full 360-degree photosphere. The end-user can pan around and view any location in this photosphere, creating a unique scenario where the optical performance at the edge of the field-of-view is just as important in the center of the image. This thesis explores the unique requirements and properties of fisheye lenses used in these systems, and a new folded fisheye lens is designed with the intent to be used in a compact virtual reality 360-degree camera. The optical system designed is an f/2.8 fisheye lens meant to be used with a 1/2.7” CMOS image sensor, which has a focal length of 1.297mm and a full-field of view of 190 degrees. This lens design utilizes a powered prism to fold the optical path after the first lens element to maintain a compact form-factor and minimize the center thickness of the imaging system when the two fisheye lens modules are placed back-to-back. The optical quality, stray-light and ghost performance, and manufacturability of the compact folded fisheye lens design are analyzed and discussed in detail.