Magnification through a lens at various diameters

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  • Thread starter Thread starter Ken Van Cleave
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    Lens Magnification
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SUMMARY

The discussion focuses on the magnification effects observed through a high power plus lens when viewing circular targets of varying diameters. It establishes that the magnification ratio between the original target diameter and the viewed diameter changes significantly with larger target sizes, despite the lens power remaining constant. The phenomenon is attributed to radial distortion, which affects the accuracy of focal length and power calculations. Participants seek formulas or methods to compensate for this distortion to maintain predictive accuracy.

PREREQUISITES
  • Understanding of lens optics, specifically high power plus lenses
  • Familiarity with magnification ratios and their calculations
  • Knowledge of radial distortion in optical systems
  • Basic principles of focal length and lens power
NEXT STEPS
  • Research methods to calculate radial distortion in optical systems
  • Explore advanced lens design techniques to minimize distortion
  • Learn about the impact of target size on optical measurements
  • Investigate software tools for simulating lens behavior and distortion effects
USEFUL FOR

Optical engineers, lens designers, and anyone involved in precision optics and imaging systems will benefit from this discussion.

Ken Van Cleave
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We have a high power plus lens of known front curve, index, and center thickness and have placed a known diameter circular target at a known distance behind the lens. Observing the circular target through the lens we compute the ratio between the diameter of the original circular target behind the lens and the measured target diameter as viewed through the lens on the other side.

Using a very small target, the focal length and power of the lens can be calculated fairly accurately using this magnification ratio along with the distance from the back of the lens to the target. The problem is that the ratio changes significantly when a larger target size is used even though the lens power is the same.

Why does this happen? Are there any formula(s) that can compensate for this so the power can still be predicted as accurately as when a very small target size is used?
 
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