Question about sign convention for R1 and R2 when using the lens maker's formula

In summary, the conversation discusses how to determine the sign for R1 and R2 when dealing with convex, planoconvex, concave, planoconcave, and meniscus lenses. The individual is confused about how to use the incident light method and came across a website that provides contradictory information. The conversation concludes with the suggestion to use the sign convention, where R1 is negative on the left side of the pole.
  • #1
chitturp
4
0
Hi!
I'm having some trouble with optics.
When we have convex, planoconvex, concave, planoconcave, and meniscus lenses, I don't understand how to substitute with the sign for R1 and R2. How do I determine whether the radius of a side is negative or positive? A book that I'm using said to take incident light in a particular direction and then measure the radius from the lens itself, but I honestly still don't understand that method at all... Then I found this:

http://www.livephysics.com/tools/optics/focal-length-for-thin-lens.html

but even though it says there that a surface "bulging out" of the lens is taken as R>0, and a surface "depressed into the lens" is R<0, it has the exact opposite shown in a few of the diagrams..

I'm confused and I would really appreciate it if someone could clarify this.
Thank you!
 
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  • #2
Use sign convention. For example R1 is negative if it lies on ghe left side of the pole.
 
  • #3
It makes sense now! Thank you!
 

FAQ: Question about sign convention for R1 and R2 when using the lens maker's formula

What is the sign convention for R1 and R2 in the lens maker's formula?

The sign convention for R1 and R2 in the lens maker's formula follows the Cartesian convention, where distances to the left of the lens are considered negative and distances to the right are considered positive. This means that a convex surface has a positive radius of curvature, while a concave surface has a negative radius of curvature.

Can the sign convention for R1 and R2 in the lens maker's formula be changed?

Yes, the sign convention for R1 and R2 in the lens maker's formula can be changed, but it is important to maintain consistency throughout calculations. In some cases, a different sign convention may be used, such as in the Gaussian lens formula.

How are the signs for R1 and R2 determined in the lens maker's formula?

The signs for R1 and R2 in the lens maker's formula are determined based on the direction of the curvature of the lens surface. If the surface is convex, the radius of curvature is positive, and if the surface is concave, the radius of curvature is negative.

Why is the sign convention important in the lens maker's formula?

The sign convention is important in the lens maker's formula because it helps to determine the direction and magnitude of the focal length of a lens. It also allows for consistent calculations and comparison of different lenses.

Can the sign convention for R1 and R2 affect the final result in the lens maker's formula?

Yes, the sign convention for R1 and R2 can affect the final result in the lens maker's formula, as it directly affects the sign of the focal length. A change in sign convention can result in a negative focal length, indicating a virtual image instead of a real image. Therefore, it is important to use the correct sign convention for accurate results.

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