Focal length of convex lens is positive or negative

Lenses used in cameras have varying focal lengths used for specific purposes. Shorter focal lengths (e.g. 18 mm) provide a wider field of view, while longer focal lengths (e.g. 55 mm) provide a smaller field of view. These lenses produce a sharp image when light converges to a specific point, called the focal point. The red dot or red square that appears in a camera's viewfinder is its focal point. Suppose that a beam of parallel rays hits a curved mirror. What will happen to the light rays? The law of reflection states that these light rays will bounce back at an angle equal to when they hit the mirror. The reflected rays will try to converge at one single point. In regular curved mirrors, most reflected rays do not converge at one point, thus producing blurred images. However, if the mirror is small enough compared to its radius of curvature, then the reflected rays will intersect at one specific point. This is referred to as focus. Most reflected rays in regular curved surfaces do not meet at one single point. This is the reason why blurred images are formed. In the figure below, the incident rays are parallel to a line called the principal axis. It is always perpendicular to the curved surface. The point where all the reflected rays converge is called the focal point, F. The distance between the vertex of the surface and the mirror's focal point is called the focal length, f. The center of curvature, C, refers to the center of the sphere by which the mirror is original...

did you see a diagram of the light rays? If so, you will see that the rays look as though they 'come from a point'. so the image LOOKS as though it should be somewhere, but really it is not. you can not shine the rays of light onto the wall and see an image on the wall. You only see an image when you eye focusses the light again to make it real (on the back of your eye) Hope that helps So Im confused, In previous videos the other instructor (Sal I think) always drew the real image of a convex lens LARGER than the object itself. Sal used 2 light rays defracting through the lens that both went through the focal points on either side of the lens to accomplish this. He also drew a diagram in his video "object image height and distance relationship", where the image was larger. SO WHY IS THE IMAGE IN THIS VIDEO SMALLER THAN THE OBJECT FOR THE CONVEX LENS?! In Sal's video, the image of an object seen through a convex lens was larger when the object was placed a distance between f and 2f from the lens. When the object is placed at a point past 2f (i.e. 2f or greater), the inverted real image is smaller. In the example used in this video, we see that f = 12cm, and the object is placed at 36cm (3f). So, the inverted real image is smaller. - [Voiceover] If I had been handed this problem on a physics test I probably would have freaked out. This looks really intimidating but it's actually not that bad. It's a classic example of a two lens system and overall, before we get lost in deta...

[ "article:topic", "paraxial approximation", "authorname:openstax", "aberration", "concave mirror", "convex mirror", "curved mirror", "focal length", "focal point", "linear magnification", "optical axis", "small-angle approximation", "spherical aberration", "vertex", "license:ccby", "showtoc:no", "coma (optics)", "program:openstax", "licenseversion:40", "source@https://openstax.org/details/books/university-physics-volume-3" ] https://phys.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fphys.libretexts.org%2FBookshelves%2FUniversity_Physics%2FBook%253A_University_Physics_(OpenStax)%2FUniversity_Physics_III_-_Optics_and_Modern_Physics_(OpenStax)%2F02%253A_Geometric_Optics_and_Image_Formation%2F2.03%253A_Spherical_Mirrors \( \newcommand\) • • • • • • • • • • • • • • • • • • Learning Objectives By the end of this section, you will be able to: • Describe image formation by spherical mirrors. • Use ray diagrams and the mirror equation to calculate the properties of an image in a spherical mirror. The image in a plane mirror has the same size as the object, is upright, and is the same distance behind the mirror as the object is in front of the mirror. A curved mirror, on the other hand, can form images that may be larger or smaller than the object and may form either in front of the mirror or behind it. In general, any curved surface will form an image, although some images make be so distorted as to be unrecognizable (think of fun house mirrors). Because curved mirrors c...

Rochelle Enrera Rochelle has a bachelor's degree in Physics for Teachers from Philippine Normal University-Manila and has completed 30+ units in MS Geology at University of the Philippines-Diliman. She is a licensed teacher and has taught Grade 10 Physics for three years. She has been a science content writer and copywriter for over three years now. • Instructor Lens A lens is an optical device, commonly made of glass or plastic, that has at least one curved side. It forms images either by allowing light to converge or diverge as it passes through it. It is found in various applications including telescopes, cameras, and eyeglasses. There are mainly two types of lenses—converging and diverging lenses. Converging, or convex, lenses have thicker centers and thinner edges. Parallel light rays refract and meet at a single point as they pass through a convex lens. Diverging, or concave, lenses have thinner centers than their edges. Unlike converging lenses, diverging lenses make the parallel light rays spread out. Converging and diverging lenses Lens Examples Lenses are found in a wide range of applications. Some of these lens examples include telescopes, cameras, magnifying glasses, microscopes, and eyeglasses. • A telescope produces large images of distant objects. It is one of the most important tools in astronomy and is used to collect data about other planets and stars. Common telescopes use two converging lenses to produce a magnified image. A Galilean telescope, which ...

A convex lens in a medium with index larger than that of the lens will act like a divergent lens, yes. This is the physical fact. If you consider the focal length positive or negative will depend on the convention used. By usual convention, the focal lens of divergent lenses is taken with minus sign. If you use the lens-maker formula (in the thin lens approximation) $$ \frac$ the focal length will be negative. Note that the formula is written with the convention that $R_2$ is negative for convex lenses so that the content of the second parenthesis on the RHS is always positive for convex lenses. If you are talking about a biconvex lens then it can not have a negative focal length if the surrounding medium is denser than the lens. As we know the formula for focal length of a thin lens( refractive index=$n_$, you can have a negative focal length. $\begingroup$ I didn't say that. You didn't mention the type of convex lens. If you consider it ti be biconvex in a denser medium then it can not have negative focal length irrespective of the relation between R1 and R2. I think you didn't undersrand what I said. Read it properly once again. $\endgroup$

\( \newcommand\) • • • An optical device such as the lens can be used for a variety of reasons:to transmit light which converges the light beam or refract light which diverges the light beam. Most lens are typically made from transparent material such as glass or plastic. The purpose of using such materials helps correct the direction of light needed in a specific situation. There are many types of lens but let's first discuss the construction of this optical device. The most abundant type of lenses is the spherical shape. There are two surfaces that are perpendicular to the axis of the lens. There can be a convex lens which looks like a bubble bulging outward or a concave lens which has an inward bulging bubble shapes. The next type of lens which is called the toric lens has 2 distinct radii of curvature that are perpendicular to each other. This creates a type of astigmatism which is where rays that propagate in two orthogonal planes have distinct foci. Although these lenses may seem simple they do certainly become more complicated. The more complex aspheric lenses have a shape that is neither spherical or cylindrical. These lenses can produce images with less aberrations. These are more adaptive lenses that can be used for digital devices (cameras). As previously mentioned, astigmatism creates a great deal of aberrations in its images and an aspheric lens can eliminate them. These lenses are great to improve visionary performance due to their ability to eliminate aberra...

An optical tool or device that tends to both converge and diverge a beam of light (based on the situation and type) through refraction, is referred to as a lens. A simple lens usually consists of only a single piece of transparent material whereas a compound lens tends to have several simple lenses (elements), that are generally arranged along a common axis. What is Convex Lens? The convex lens is a lens that converges rays of light that convey parallel to its principal axis (i.e. converges the incident rays towards the principal axis) which is relatively thick across the middle and thin at the lower and upper edges. The edges are curved outward rather than inward. It is used in front of the eye to bend the incoming light sharply so the focal point shortens and the light focuses properly on the retina. Generally, a convex lens can converge a beam of parallel rays to a point on the other side of the lens. This point is called a focus of the lens and its distance from the Optical Center of the beam is called the focal length. The radius of curvatures R1 and R2 of the spherical surfaces and the focal length of the lens ‘f’ are connected by an approximate equation. For Mathematical Equation: \[ \frac)\] Where, n is the refractive index. R 1 and R 2 are the radii of curvature. R 1 is denoted as the surface very near to the light source. R 2 is denoted as the surface very far from the light source. In the case of Double Convex Lens, the focal length is greater due to the presenc...

Previous Section Focal Length The focal length of a lens is a fundamental parameter that describes how strongly it focuses or diverges light. A large focal length indicates that light is bent gradually while a short focal length indicates that the light is bent at sharp angles. In general, lenses with positive focal lengths converge light while lenses with negative focal lengths cause light to diverge, although there are some exceptions based on the distance from the lens to the object being imaged. Field of View Field of view describes the viewable area that can be imaged by a lens system. This is the portion of the object that fills the camera’s sensor. This can be described by the physical area which can be imaged, such as a horizontal or vertical field of view in mm, or an angular field of view specified in degrees. The relationships between focal length and field of view are shown below. Fixed Focal Length Lenses A angular field of view (AFOV). By focusing the lens for different working distances (WDs), differently sized field of view (FOV) can be obtained, though the viewing angle is constant. AFOV is typically specified as the full angle (in degrees) associated with the horizontal dimension (width) of the sensor that the lens is to be used with. Note: Fixed focal length lenses should not be confused with fixed focus lenses. Fixed focal length lenses can be focused for different distances; fixed focus lenses are intended for use at a single, specific WD. Examples of ...

The correct option is B Convex lens has positive focal length and concave lens has a negative focal length. Focus of converging or convex lens is at the right hand side of the lens, hence focal length is positive. Focus of diverging or concave lens is at the left hand side of the lens, hence focal length is negative. Q. Question 8 Which of the following statements is true? (a) A convex lens has 4 dioptre power having a focal length 0.25 m. (b) A convex lens has -4 dioptre power having a focal length -0.25 m. (c) A concave lens has 4 dioptre power having a focal length 0.25 m. (d) A concave lens has 4 dioptre power having a focal length -0.25 m.