Current Optics and Photonics

Optical Society of Korea (한국광학회)
권호 표지
DOI QR코드

DOI QR Code

Measurement of Focal Length for Off-axis Optical Systems

  • Choe, Se-woon (Department of Medical IT Convergence Engineering, Kumoh National Institute of Technology) ;
  • Ryu, Jaemyung (Department of Optical Engineering, Kumoh National Institute of Technology)
  • Received : 2021.02.15
  • Accepted : 2021.04.09
  • Published : 2021.08.25
Download PDF
⟨ Previous Next ⟩

Abstract

An off-axis system refers to an optical system in which the optical axis and normal vector at the vertex of each surface do not match. The most important specification in an optical system is its focal length. Among the various methods for measuring the focal length, the most suitable method for the off-axis system is the method that adopts magnification. However, head-mounted display (HMD) optics must be measured while considering the virtual image distance, which is not infinity owing to product characteristics. For the virtual image distance, a camera with a focusing function was used. By measuring HMD optics via this magnification method, the error generated in this measurement was 0.68% of the HMD's focal length, which is within the 1%-3% range of the conventionally permitted design error for the focal length allowed at the optical design stage. Therefore, it can be verified that the measurement accuracy of the method proposed in this study is sufficiently feasible in practice.

Keywords

Acknowledgement

This research was supported by a grant from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF2020R1I1A3052712), the Korean government (MSIT) (NRF-2019R1F1A1062397), and Brain Korea 21 FOUR Project (Department of IT convergence engineering, Kumoh National Institute of Technology). This research was supported by the MSIT (Ministry of Science and ICT), Korea, under the Grand Information Technology Research Center support program (IITP-2021-2020-0-01612) and supervised by the IITP (Institute for information & communications technology planning & evaluation).

References

  1. S. Chang and A. Prata, "Geometrical theory of in classical aberrations off-axis reflecting near the axis telescopes," J. Opt. Soc. Am. A 22, 2454-2464 (2005). https://doi.org/10.1364/JOSAA.22.002454
  2. G. D. Miller, "See-through display with an optical assembly including a wedge-shaped illumination system," US Patents 8467133B2 (2013).
  3. J. Rolland, and H. Hua, Encyclopedia of optical engineering, R. G. Driggers, C. Hoffman, R. Driggers, Eds., 1st ed. (CRC Press, FL, USA. 2003), pp. 1-13.
  4. Hyndai Motors, "AR Head up display (HUD)", (HMG Journal, Published date: 2017), https://news.hmgjournal.com/Tech/?p=151553 (Accessed date : July 19, 2021).
  5. S. H. Seo, J. M. Ryu, and H. Choi, "Focus-adjustable head mounted display with off-axis system," Appl. Sci. 10, 7931 (2020). https://doi.org/10.3390/app10217931
  6. Japanese Standards Association, JIS Handbook ISO 9000 2013 (Japanese Standards Association, Tokyo, Japan. 2013).
  7. W. J. Smith, Modern Optical engineering, 4th ed. (McGrew-Hill, NY, USA. 2007).
  8. K. Cho, J.-H. Seo, G. Heo, and S.-W. Choe, "An alternative approach to detecting cancer cells by multi-directional fluorescence detection system using cost-effective LED and photodiode," Sensors 19, 2301 (2019). https://doi.org/10.3390/s19102301
  9. D. Bradley and G. Roth, "Adapting thresholding using the integral image," J. Graph. Tools 12, 13-21 (2007). https://doi.org/10.1080/2151237X.2007.10129236
  10. D. Baskin, R. Butler, R. Sanyal, and J. Keller, "Samsung NX1 Review," (Digital Photography Review, Published date: April 9, 2015), https://www.dpreview.com/reviews/samsung-nx1(Accessed date: 2021).
  11. Digital Photography Review, "Samsung NX 20mm F2.8 Pancake Overview," (Digital Photography Review, Published date: September 14, 2010) https://www.dpreview.com/products/samsung/lenses/samsung_20_2p8 (Accessed date: 2021).
  12. Trioptics, " ImageMaster® HR/HR TempControl/Universal," (Trioptics), https://trioptics.com/products/imagemaster-hruniversal-image-quality-mtf-testing/ (Accessed date: 2021).