How Can a Near Object Be Focused While Looking at Distant Objects?

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SUMMARY

To focus on a near object while simultaneously viewing distant objects, a small convex (magnifying) lens is effective. This technique is exemplified by the use of a prismatic compass, which allows users to see both a nearby compass card and distant landmarks clearly. The discussion confirms that a positive fresnel lens is not necessary for this purpose, as a standard convex lens suffices. This method is particularly useful for individuals with limited experience in optics.

PREREQUISITES
  • Understanding of basic optics principles
  • Familiarity with lens types, specifically convex lenses
  • Knowledge of prismatic compass functionality
  • Awareness of visual acuity and focusing techniques
NEXT STEPS
  • Research the properties and applications of convex lenses in optics
  • Explore the design and usage of prismatic compasses
  • Learn about bifocal lenses and their advantages for vision correction
  • Investigate the principles of focal length and depth of field in photography
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Optics enthusiasts, amateur astronomers, and individuals seeking to improve their understanding of lens applications in practical scenarios.

jstwinkles
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Hi, I have what might seem like an odd question. Suppose that someone is looking at an object in the distance, and there is an object placed about an inch in front of one of the person's eye. Obviously, this object would appear out of focus. My question is this: how would one bring this object into focus so that when the person is looking at distant objects it appears in focus? Could a small positive fresnel lens be used? If not, any ideas on how to go about doing this or any alternatives? Sorry if this sounds like a vague question, I have relatively little experience in optics.

Thanks ahead of time.
 
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A small convex (magnifing) lens does the trick. For example an prismatic compass uses such a lens to allow the user to view the moving compass card (a couple inches from the eye) and a landmark in the distance (miles away) at the same time for accurate readings.
 
jstwinkles said:
Hi, I have what might seem like an odd question. Suppose that someone is looking at an object in the distance, and there is an object placed about an inch in front of one of the person's eye. Obviously, this object would appear out of focus. My question is this: how would one bring this object into focus so that when the person is looking at distant objects it appears in focus? Could a small positive fresnel lens be used? If not, any ideas on how to go about doing this or any alternatives? Sorry if this sounds like a vague question, I have relatively little experience in optics.

Thanks ahead of time.

bifocals?
 
drummin said:
A small convex (magnifing) lens does the trick. For example an prismatic compass uses such a lens to allow the user to view the moving compass card (a couple inches from the eye) and a landmark in the distance (miles away) at the same time for accurate readings.

Thanks, drummin, that's exactly what I needed to know! I appreciate it.
 
drummin said:
A small convex (magnifing) lens does the trick. For example an prismatic compass uses such a lens to allow the user to view the moving compass card (a couple inches from the eye) and a landmark in the distance (miles away) at the same time for accurate readings.

Very interesting. I did not know that could be done. Thanks.
 

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