If you are looking for more details, kindly visit optec.
Thread starter
physics user1
Start date
Mar 27,Tags
It may be that a source uses a different convention or different sign convention. If you know what should happen in a simple case, you can figure out what they're doing and adjust accordingly.In summary, when considering the orientation of a plan convex lens, it does not affect its focal length. However, flipping the lens can affect aberrations and it is important to be careful with sign conventions in optics. It is recommended to keep a simple case in mind and adjust accordingly for different conventions.
physics user1
Does the orientation of a plan convex lens affect it's focal lenght?
If I put il like in the first example in the photo and makeep the calculation using the lens maker equation I get f positive
What happens if I turn the curved face on the right?
Using the lens maker equation now the radius is negative so the focal length should be -f...
Is that Right?
Mentor
Cozma Alex said:
Cozma Alex said:
It does not.That not correct. The lens maker equation has two terms in it that matter here: ##\frac{1}{R1}-\frac{1}{R2}##If you flip your lens around, the sign of the radii of curvatures change, but then surface 1 becomes surface 2 and vice versa. If R1 is initially 100 and R2 is ', then ##\frac{1}{100}-\frac{1}{'} = 0.01 - 0 = 0.01##Flip the lens around and you get: ##\frac{1}{'}-\frac{1}{-100} = 0 - (-0.01) = 0.01##
Science Advisor
Insights Author
Clearly not. Imagine a symmetric biconvex lens - that would have zero power if you were correct.
You need to be careful with sign conventions in optics. If you are switching signs on your radius of curvature when you switch sides then the relevant formula uses ##(1/r_1-1/r_2)## so you get the same overall sign. Sometimes you see the convention that all convex curves are positive, but that would give ##(1/r_1+1/r_2)##.
Edit: It does affect aberration. Best to put the curved face on the side where the rays are nearer parallel.
physics user1
Thank you guys I got it now
physics user1
But, how do I choose surface one and 2?
Science Advisor
Insights Author
Surface 1 has the lower x coordinate of you're using the ##(1/r_1-1/r_2)## form. It doesn't matter if you're using the other form.
Keep in mind a simple case, such as a biconvex lens. You know that f is positive. That let's you make a workable choice for convention: both positive and use ##(1/r_1+1/r_2)##, or surface 1 positive and 2 negative and use ##(1/r_1-1/r_2)##. Then you can flip signs as appropriate for the surfaces of the lens you actually have.
physics user1
Correct? The surface 1 is then the firSt thwt the light hits
Science Advisor
Insights Author
It's all just convention. Usually light rays enter the system from the left, moving to the right, which is the +x direction. And curvatures are defined as positive if the inside of the curve is on the +x side of the surface. And ##r_1## would be the radius of the first surface. In that case, yes you are right.
But I advise you to keep a simple case (e.g. a symmetric biconvex lens) in mind and figure out the signs as you go. With the symmetric biconvex lens you know that the two ##1/r## terms must end up with positive signs somehow (either because the radii have opposite signs and the two terms do too or because the two terms have the same sign and so do the radii) because otherwise the power is zero.
Then you won't be fooled by people picking different conventions.
A plano convex lens is a type of lens that has one flat surface and one convex surface. It is commonly used in optical instruments to focus light.
The focal length of a plano convex lens is determined by the curvature of the convex surface and the refractive index of the material it is made of. It is the distance between the lens and the point where parallel rays of light converge after passing through the lens.
The focal length of a convex lens is positive, meaning that the point of convergence is in front of the lens. On the other hand, the focal length of a concave lens is negative, meaning that the point of convergence is behind the lens.
Yes, the focal length of a plano convex lens can be changed by changing the curvature of the convex surface or the refractive index of the material it is made of. This can be done by using different materials or shaping the lens differently.
Plano convex lenses are commonly used in telescopes, microscopes, cameras, projectors, and other optical instruments. They are also used in laser systems, medical devices, and automotive headlights.
Image Formation with Converging Lenses - Java Tutorial
Positive, or converging, thin lenses unite incident light rays that are parallel to the optical axis and focus them at the focal plane to form a real image. This interactive tutorial utilizes ray traces to explore how images are formed by the three primary types of converging lenses, and the relationship between the object and the image formed by the lens as a function of distance between the object and the focal points.
The tutorial initializes with an object (represented by a vertical gray arrow on the left-hand side of the lens) positioned more than twice the distance of the focal length away from a simple thin bi-convex lens. Ray traces emanating from the point of the object arrow (Object) pass through various points on the lens and are reunited at the apex of an inverted arrow (the Real Image) on the opposite, or image, side of the lens. Three of the rays are illustrated in red: the Principal Ray, which passes through the center of the lens, and two additional characteristic rays. One of the characteristic rays passes through the lens front focal point (F), while the other travels toward the lens parallel to the Optical Axis and crosses the axis at the rear focal point (F'). Any two of these three rays can be utilized to determine the size and placement of the image formed by the lens.
In order to operate the tutorial, use the Object Position slider to translate the object arrow back and forth along the optical axis of the lens. As the object is moved closer to the lens, the image size increases and moves farther away from the lens. In contrast, as the object is moved away from the lens, the image moves closer to the lens and grows smaller. The distance between the lens and the object (Object Distance, (p)) and image (Image Distance, (q)) are continuously updated in the lower left-hand corner of the tutorial window. The bi-convex lens can be changed to either a Positive Meniscus or Plano-Convex element by selecting the appropriate choice using the pull-down menu.
As shown in Figure 1, positive lenses have one or two convex surfaces and are thicker in the center than at the edges. A common characteristic of positive lenses is that they magnify objects when they are placed between the object and the human eye. The primary lens geometries for the positive lens elements illustrated in Figure 1 are bi-convex (Figure 1(a)) and plano-convex (Figure 1(b); having one planar or flat surface). In addition, the convex-meniscus (Figure 1(c)) lens has both convex and concave surfaces with similar curvatures, but is thicker in the center than at the edges. Bi-convex lenses are the simplest magnifying lenses, and have a focal point and magnification factor that is dependent upon the curvature angle of the surfaces. Higher angles of curvature lead to shorter focal lengths due to the fact that light waves are refracted at a greater angle with respect to the optical axis of the lens. The symmetric nature of bi-convex lenses minimizes spherical aberration in applications where the image and object are located symmetrically. When a bi-convex optical system is fully symmetric (in effect, a 1:1 magnification), spherical aberration is at a minimum value and coma and distortion are equally minimized or cancelled. Generally, bi-convex lenses perform with minimum aberrations at magnification factors between 0.2x and 5x. Convex lenses are primarily employed for focusing applications and for image magnification.
Typical plano-convex lenses (Figure 1(b)) have one positive convex face and a flat (plano) face on the opposite side of the lens. These lens elements focus parallel light rays into a focal point that is positive and forms a real image that can be projected or manipulated by spatial filters. The asymmetry of plano-convex lenses minimizes spherical aberration in applications where the object and image lie at unequal distances from the lens. The optimum case for reduction of aberration occurs when the object is placed at infinity (in effect, parallel light rays enter the lens) and the image is the final focused point. However, the plano-convex lens will produce minimum aberration at conjugate ratios up to approximately 5:1. When the curved surface of a plano-convex lens is oriented toward the object, the sharpest possible focus is achieved. Plano-convex lenses are useful for collimating diverging beams and to apply focus to a more complex optical system.
The positive meniscus lens (Figure 1(c)) has an asymmetric structure with one face shaped as a convex radius, while the opposite face is slightly concave. Meniscus lenses are often employed in conjunction with another lens to produce an optical system having either a longer or shorter focal length than the original lens. As an example, a positive meniscus lens can be positioned after a plano-convex lens to shorten the focal length without decreasing optical system performance. Positive meniscus lenses have a greater curvature radius on the concave side of the lens than on the convex side, enabling formation of a real image.
Matthew Parry-Hill, Robert T. Sutter and Michael W. Davidson - National High Magnetic Field Laboratory, East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, .
If you want to learn more, please visit our website Micro Prisms for Endoscopy.