How to shift a focal point af an objective

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    Focal Point Shift
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SUMMARY

The discussion centers on shifting the focal point of a 50 mm focal length objective lens to accommodate a CCD camera positioned 1-2 cm behind the objective. The recommended solution involves using a negative lens in series with the objective to effectively translate the focal point, although this may reduce image sharpness and coverage. Alternative suggestions include using a positive lens with a short focal length or a system of two plano-convex lenses to maintain 1:1 magnification. Participants agree that while sharpness reduction is acceptable, the choice of lens configuration is critical for optimal performance.

PREREQUISITES
  • Understanding of optical systems and lens types
  • Knowledge of focal length and magnification principles
  • Familiarity with lens combinations and their effects on image quality
  • Basic concepts of CCD camera positioning and optics
NEXT STEPS
  • Research the effects of negative lenses on focal length and image quality
  • Learn about plano-convex lens configurations and their applications
  • Explore the principles of compound lenses in optical systems
  • Investigate methods for maintaining 1:1 magnification in lens systems
USEFUL FOR

Optical engineers, hobbyist photographers, and anyone involved in designing or modifying optical systems for CCD cameras.

martim
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Hi, i have a simple optical system composed of:

1. objective with 50 mm focal lenght

2. CCD camera that can not be mounted behind the objective, for mechanical reasons... it can only be mounted 1-2 cm far behind the objective.

So i need to "translate" the focal point of the objective 1-2 cm behind the ojcetive original focal point.

How can i do this?? Have i two use one or at least two lenses?

Thanks in advance!
 
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You can add a negative lens in "series" to increase the focal length. See http://en.wikipedia.org/wiki/Lens_(optics ) "compound lenses". But this will change the image coverage, just like putting a telephoto lens on your camera, and -- maybe you don't care -- likely reduce the sharpness a bit.
 
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Hi, thanks for your answer... a reduction of the sharpness is not a problem...

A question: why a negative lens? I though about two solutions (but maybe the are not the best choice...)

1. a positive lens (diam. 6 - 10 mm) with a focal as shot as possible... few millimeters, posizioned symmetrycally between the focus of the objective and the CCD... to maintain the 1:1 magnification

2. a system comped by two piano convex lenses

what is, in your opinion, the best solution?

bye!
 

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