Nature of Convex Lens Shadows – Lenses are one of the important items in human life, both lenses used for aesthetics and lenses used to assist research. There are also lenses that have various types depending on the need or purpose of using the lens. One type of lens that is quite popular and familiar is a convex lens.
A convex lens is a type of lens that is thicker in the center than at the edges, either a convex lens or a concave lens is a type of thin lens based on its surface. The lens itself can be interpreted as transparent glass that has a curved surface.
The surface of the lens can produce different refractive effects. So, so that Sinaumed’s can study material related to convex lenses further, here’s an explanation of the meaning of a convex lens and the nature of the image of a convex lens.
Definition of Convex Lens
The lens is a clear object bounded by two refractive planes. A convex or convex lens is a type of lens that is thicker in the middle than at the edges.
You could say that a convex lens has a bulging center. Convex lenses generally have a circular shape and are made of glass or plastic, so a convex lens has a higher index of refraction than air.
A convex lens is also known as a positive lens. A convex lens has the property of being able to gather light, so a convex lens is also known as a converging lens. If there is a beam of light parallel to the main axis and the light hits the surface of the lens, then the light beam will be refracted through one point.
From the picture above, it can be seen that the refracted rays gather at a single focal point which is behind the lens. Unlike a mirror which has only one focal point, a lens generally has two focal points.
The focus point is the meeting point of the refractive rays and is referred to as the main focus or F1, also known as the active focus. Because in a convex lens the refractive rays gather behind the lens, the location of the F1 is behind the lens. Meanwhile, the passive focus point or F2 is symmetrical with F1. for a convex lens, the location of F2 is in front of the lens.
Types of Convex Lenses
Based on the shape of the curved surface, convex lenses are divided into three, namely biconvex lenses, convex planes and convexconcave lenses. Here’s an explanation.
1. Biconvex convex lens (double convex lens)
A type of biconvex convex lens is a lens that has two convex surfaces.
2. Convex plan convex lens (flat convex lens)
A convex lens has one convex surface and one flat surface. This type of convex lens with two surfaces is called a convex plane convex lens.
3. Concave convex lens
The third type of convex lens is a convex lens which has one convex surface and the other is concave. However, the convex surface tends to be more dominant than the concave surface.
So that Sinaumed’s can better understand what a convex lens is, consider the image below.
A convex lens has 7 main parts, among which are the following:
 The main axis, namely the line A to B, is a line perpendicular to the lens.
 The optical center, O, is also known as the vertex point. The vertex point is a meeting point between the main axis and the lens.
 The focal point or focal point, which is in front of the F1 is the dkus which is in front of the convex lens.
 The focal point or focal point, behind F2 is the focus behind the convex lens.
 Points O to F are referred to as the focal length of a convex lens.
 The 2F point is called the center of curvature of a convex lens.
 Points O to 2F are also known as the radius of curvature on a convex lens.
From the explanation regarding the definition of a convex lens above, it can be concluded that a convex lens has three characteristics, namely: a) the center is thicker than the edges, b) has the property of gathering light or converging properties, c) has a positive focus value, So the convex lens is also known as a positive lens.
Properties of a convex lens
Convex lenses have several properties that differentiate them from other types of lenses. The following is an explanation of the properties of a convex lens:
 In a convex lens, light can come from two directions, so a convex lens has two focal points. The front convex lens is where the light comes from while the rear convex lens is where the light is refracted.
 If there are three rays coming in parallel, then directed at a convex lens, then the rays from these rays will be refracted by the lens and intersect or go to a point. The focus point on the front of the convex lens is called the virtual focus point or passive focus with the symbol F2, while the focus point on the back of the convex lens is called the true focus point or active focus point with the symbol F1.
 Convex lenses have the property of gathering or converging. Because the light that comes through a convex lens is always refracted towards one point or collects light, a convex lens is called a converging lens or collecting lens.
 The focal length of the convex lens is always positive, because the intersection or destination of the refractive rays is always at the back of the convex lens, so the focus of the convex lens is a true focus.
 The amount of light refraction in a convex lens is affected by the refractive index of the lens material and the curvature of the lens surface. Meanwhile, the index of refraction depends on how fast or slow the light is in the lens.
 A convex lens with a thicker size can produce a greater refraction of light as well, compared to a convex lens with a thinner thickness. In addition, a thick convex lens also produces a shorter lens focal length, compared to a thin convex lens.
Properties of the Image of a Convex Lens
After knowing the properties of a convex lens, here’s an explanation of the nature of the image from a convex lens.
1. The object is between points O and F

A’B’ = Virtual image is in front of the lens
 F1 = Focus is behind the lens
 F2 = Focus is in front of the lens
The nature of the image above is virtual, upright and magnified.
2. The object is between points F2 and 2F2
The image of object A’B’ is real, inverted and magnified.
3. The object is between point F2 to ~
A’B”s image is inverted, real and diminished.
From the three pictures above, if the object is between points O and F, then the nature of the image is upright, full and magnified. Meanwhile, if the object is between points F and 2F, then the nature of the image is inverted, real and magnified.
 If S = F the image is upright, virtual and infinite.
 If S = 2 F the image has real, inverted and the same size.
 If S > 2F, the image is inverted, real and diminished
 Shadow magnified s′ > s, the image is reduced if s′ < s. (caption= –5 = 5 or 5 = 5).
4. The object is at the focal point F
Objects that are at the focal point or F, objects at the focal point (s = f), images that are easy to observe have upright, virtual and magnified properties.
5. Objects are at 2F (s= 2F)
Objects that are at 2 F (s= 2F) have real, inverted and equal image properties. Objects that are at 2F2, the image of 2F1 has real, inverted and the same size.
From the five pictures above, it can be concluded as follows:
 All virtual images formed by a convex lens are always perpendicular to the object.
 All real images formed by a convex lens will be inverted on the object.
Special Rays of Convex Lenses
There are three special rays that a convex lens has, here are the three special rays:
 Rays coming parallel to the principal axis will be refracted through the focal point (F) behind the lens.
 The incoming light goes to the focal point in front of the lens (F2), it will be refracted parallel to the main axis.
 Rays coming through the center of the optical lens (O) will be forwarded and not refracted.
Convex Lens Formula
There are several formulas that can be used for convex lenses, here are the explanations:
1. Formulas for object distance, image and focus from a convex lens
The formula for object distance, image and focus or focal point of a convex lens can be written using the following mathematical equation:
1/s + 1/s’ = 1/1
Information:
 s = object distance (m or cm)
 s’= distance from the image (m or cm)
 f= distance from focus (m or cm)
Notes:
If s’ has a positive value, then the image behind the lens is real. Meanwhile, if s’ has a negative value, then the image in front of the lens is virtual.
2. The formula for the height or magnification of the image on a convex lens
The formula for the height or magnification of the image in a convex lens can be written using the following mathematical equation:
h’/h = s’/ s = M
Information :
 h’= shadow height (m or cm)
 h=height of the object (m or cm)
 s’= height of the shadow (m or cm)
 s=height of the object (m or cm)
 M = magnification of the image
3. The formula for the radius of curvature and index of refraction for a convex lens
The formula for the radius of curvature and refractive index of a convex lens can be written using the following mathematical equation:
1/F = (n2/n1 – 1) (1/R1 + 1/R2)
Information :
 F = focal length (m or cm)
 n1 = index of refraction around the convex lens
 n2 = index of refraction of the lens
 R1 = radius of curvature that is in front of the lens
 R2 = radius of curvature that is behind the lens
4. Formula for the power of a convex lens
The formula that can be used to calculate the power of a convex lens can be written using the following mathematical equation:
P = 1/F
Information :
P = power on a convex lens or diopters
It is important to note that the following is the convention for the sign of a convex lens:
 F convex lens always has a positive value
 + s for the real object to be in front of the lens
 – s for virtual objects is behind the lens
 +s’ for the real image is behind the lens
 s’ for the virtual image is in front of the lens
 +M for an upright shadow
 M for an inverted shadow
The Benefits of Convex Lenses in Everyday Life
A convex lens has the function of being able to focus on the incoming light beam. So that light entering through the front surface will be refracted at one point by the back surface of the convex lens.
Then, in everyday life, convex lenses are often used by humans in various kinds of equipment and technology. Here are some examples of the use of convex lenses in everyday life:
1. Lup or magnifying glass
A loupe is an optical instrument whose function is to see small objects so that they appear larger. This tool is a fairly simple tool, because it only consists of a convex lens and a support or frame if needed.
A watchmaker is someone who most often uses a lup or magnifying glass. By using a lup, small parts of the movement will appear larger and clearer.
2. Microscope
The nature of the convex lens is that it can make the image bigger, so the nature of the convex lens is used in a microscope. In a microscope, there are two convex lenses used, namely the lens facing the object or objective and the lens facing the eyepiece.
A convex lens that is placed opposite the object has the function of forming a real and inverted image, while a convex lens that is close to the eye has the function of forming an upright, virtual and magnified image.
3. Camera
The camera is one of the items that are familiar to use today, the camera can be used because it utilizes a convex lens, so that it forms a real, inverted and reduced image. Shadows in the photo must be at a distance of more than 2F and F is the focus of the lens. The convex lens on the camera is placed in a row so that it can produce photos or videos.
4. Binoculars
Binoculars are a tool used to see objects that are far away. Binoculars can be used because they use two convex lenses, just like a microscope.
The two convex lenses used are lenses that are placed facing the object or objective and lenses that are placed facing the eye or eyepiece.
The convex lens that is directly opposite the object or objective has the function of gathering light, while the convex lens that is facing the eye has the function of magnifying the image.
5. Glasses
Convex lenses in glasses are used specifically for people with nearsightedness or hypermetropia. People with hypermetropia cannot see objects clearly, because the image of the object falls behind the retina.
Therefore, the way to overcome it is to use glasses made of convex lenses. The convex lens has the function of adjusting the image of objects close to the eye, so that it falls on the retina.
That is an explanation of the image of a convex lens and its general characteristics. Hopefully all the discussion above is useful for you. Sinaumed’s who want to deepen other Physics material, can get more information by reading books.