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

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Discussion Overview

The discussion centers around the question of how to bring a near object into focus while simultaneously looking at distant objects. It explores concepts related to optics, specifically the use of lenses to achieve this effect.

Discussion Character

  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant inquires about the possibility of using a small positive fresnel lens to focus on a near object while looking at distant objects.
  • Another participant suggests that a small convex lens can achieve the desired effect, referencing the use of such lenses in prismatic compasses to view both nearby and distant objects simultaneously.
  • A later reply mentions bifocals as a potential solution, indicating an interest in alternative methods for achieving focus.

Areas of Agreement / Disagreement

There appears to be some agreement on the use of convex lenses for this purpose, but the discussion includes multiple suggestions and does not reach a consensus on the best approach or the effectiveness of alternatives like bifocals.

Contextual Notes

Participants express varying levels of experience with optics, which may influence their understanding and suggestions. The discussion does not resolve the effectiveness of different lens types or methods proposed.

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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