Point action camera or other digital video cameras, as they are referred to herein, go by many other names, including point of view cameras (see, e.g., pointofviewcameras.com), helmet cameras, action cams or action cameras, point of view shooter cams, video action cameras, and extreme sports cameras among others. Brand names include GoPro and ReplayXD. Conventional point action cameras or other digital video cameras capturing images at a wide field of view typically have significant distortion, particularly at the outer several degrees of the wide field of view. In addition, astigmatism errors in conventional point action cameras or other digital video cameras can negatively impact the appearance of the video images that it captures. It is desired to have a point action camera or other digital video camera that is capable of capturing a wide field of view, or a field of view that is greater than 90 degrees in either or both of the horizontal (x) and/or vertical (y) dimensions (or an arbitrary axis normal to the depth (z) dimension), and in certain embodiments greater than 120 degrees, and perhaps 135-150 degrees or more in the horizontal (x) dimension and/or perhaps 110-120 degrees or more in the vertical (y) dimension, and that is configured with built-in distortion and astigmatism error compensation, as well as residual oblique aberrational error compensation.
Distortion in wide field of view cameras has been reduced with image processing software (see, e.g., U.S. Pat. Nos. 8,493,459 and 8,493,460, and US published patent applications nos. 2011/0216156 and 2011/0216157). It is desired however to alternatively provide a point action camera or other digital video camera, wherein the distortion that is typically inherent in wide field of view systems such as conventional point action cameras or other digital video cameras is compensated by an effective and efficient optical design.
Alex Ning describes a six lens design in U.S. Pat. No. 7,023,628 that has a ratio of total track length (TTL) to effective focal length (EFL), or TTL/EFL, that has a maximum value of 15 over which Ning states that the design would not have been considered compact. The Ning six lens design also has a minimum value of 8 under which Ning states that the design would not achieve the required fish eye field of view. U.S. Pat. No. 7,929,221 describes multiple optical assemblies that each include three aspheric surfaces on two lens elements and that each have a TTL/EFL ratio between 15 and 25. In an unrelated technical field, U.S. Pat. No. 7,675,694 nonetheless describes multiple optical assemblies that each include six aspheric surfaces on three lens elements. At U.S. Pat. No. 8,873,167, Ning describes an optical system that includes three lens elements in the first group and either having no aspheric lens elements or two aspheric lens elements, one in each of the two optical groups. In one example, Ning discloses a TTL/EPL ratio of 17.6, while in more compact examples TTL/EFL is described as being not less than 8. It is desired to have an optical assembly for a compact camera that exhibits a wide field of view with low distortion and that has a TTL/EFL ratio that is less than 8.
It is recognized by the present inventors that it would be advantageous to have a design with a lower TTL/EFL ratio, which takes into account the desire for compactness in physical size as well as the desire to have point action video and other digital video with a wide field of view without intolerable amounts of distortion and astigmatism errors, nor errors from residual oblique aberrations. It is desired therefore to have an optical system for a point action camera or other digital video camera or other digital camera that has a low TTL/EFL ratio and that also achieves a desired wide field of view with tolerable, minimal, insubstantial, insignificant or drastically reduced distortion, astigmatism and residual oblique aberrational characteristics.
Wang et al. have proposed at U.S. Pat. No. 9,019,629 an optical assembly for a mobile phone camera that exhibits a ratio of the sensor diagonal to the focal length between 1.27 and 1.55. The optical assembly of Wang et al. is not configured for capturing images at a wide field of view.