How do I accurately measure the size of an object using CCTV lenses?

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SUMMARY

The discussion focuses on accurately measuring the size of an object using CCTV lenses, specifically a lens with a focal length of 12mm. The user clarifies that the nodal points of the lens coincide with the principle planes, given that the surrounding medium is air. The user also confirms that the focal length is measured from the mounting surface of the lens, not from the last element. The thread concludes with the user expressing confidence in their understanding of the topic.

PREREQUISITES
  • Understanding of nodal points and principle planes in optics
  • Knowledge of focal length measurement in CCTV lenses
  • Basic principles of ray tracing in lens systems
  • Familiarity with pixel measurement in digital imaging
NEXT STEPS
  • Research the principles of ray tracing in optical systems
  • Learn about the impact of focal length on image size in CCTV applications
  • Explore methods for converting pixel dimensions to real-world measurements
  • Investigate different types of CCTV lenses and their specifications
USEFUL FOR

Optics enthusiasts, CCTV technicians, and anyone involved in measuring objects using digital imaging techniques will benefit from this discussion.

bobjim
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[SOLVED] Understanding CCTV lenses

Hey guys, I'm trying to get my head around the way a lens works...

I've found the nodal points, and since the medium surrounding the lens is air constant refractive index (air) then they nodal points coincide with the principle planes, right?

Also the Focal length of the lens is 12mm, which I assume since it's a CCTV lens, is measured from the mounting surface rather than the last element of the lens... is that a fair assumption?

I've drawn a diagram of what I think represents the path of a ray going through the lens. (see attached) What I'm trying to do is accurately measure the size of something from it's size in pixels in the image.
 

Attachments

  • Lens Principle Planes.png
    Lens Principle Planes.png
    7.3 KB · Views: 521
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damn, I talk some rubbish sometimes! *think* I've figured it all out now... ignore everything above! If an admin want's to close/delete this thread, please feel free.
 

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