How to determine a lens width?

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  • Thread starter Thread starter clalburn1420
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    Lens Width
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Discussion Overview

The discussion revolves around determining the width of a lens required to focus an image at a specific distance, particularly when an object is placed directly on the lens. The scope includes theoretical considerations of lens shape, focal length, and practical implications of lens placement.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions how to determine the width of a lens when an object is placed directly on it, aiming for a projected image to focus at around 3 cm.
  • Another participant notes that the width alone is insufficient, emphasizing the importance of the lens curvature and focal length, referencing the lens formula 1/f = 1/u + 1/v.
  • A different participant agrees that the lens must be convergent and suggests that while the equation can find focal length, it does not specify the lens shape.
  • One participant cautions against placing an object in contact with the lens, questioning the feasibility of forming an image at a finite distance.
  • A participant expresses curiosity about the possibility of focusing an image with the object very close to the lens, such as 1 mm away, and asks if this is achievable.
  • Another participant confirms that focusing is possible if the lens has the correct focal length, likening it to the function of a microscope objective.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility and methodology of determining lens width and shape, indicating that multiple competing perspectives remain without a consensus.

Contextual Notes

Participants have not resolved the implications of lens shape on width determination, nor the practical limitations of placing an object directly on the lens.

clalburn1420
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I am wondering... say an object was put directly on a lens and you wanted the projected image to focus at around 3 cm on the other side. How do you determine how wide the lens has to be?
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"how wide" in itself is not enough to specify this, since the angle of incedence depends on the curvature of the lens. you must look for a lens wth the correct focal length, where
1/f = 1/u + 1/v (if I'm remembering correctly)

the top bit of this page explains...
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/lenseq.html
 
Ah, so it is also determined by the shape. However, i expect it would need to be a convergent lens type and assume it needs to be like a () shaped lens. The problem is however, that this equation can help find focal length but not describe how the lens itself will be shaped.
 
Placing an object directly in contact with a lens (any lens) is not a good way to form an image any finite distance away from the lens. Why do you want to do this?
 
Simply curious if its possible. I'm not sure it is, which is why I'm wondering. What about if the object is a very small distance from the lens, like say 1 mm. Can you focus the image on the other side 3 cm away?
 
Sure, if the focal length of the lens is correct. That's how a microscope objective works.
 

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