Introduction
Optical zoom is a feature of many cameras and binoculars that allows one to zoom in on a subject without losing image quality. Optical zoom works by physically adjusting the lens inside the camera or binoculars, which changes the focal length and magnification of the image. Usually, optical zoom systems are complex with many optical components, here we will focus on simple systems with up to three lenses for simplicity and educational purposes.
In an optical zoom system, there are usually several lens elements that work together to produce a clear, high-quality image. These lens elements are arranged in groups and move back and forth inside the camera or binoculars when you zoom in or out.
Optical zoom systems are often described in terms of their zoom ratio, which is the maximum magnification divided by the minimum magnification. For example, a camera with a zoom ratio of 10x can zoom in up to 10 times closer to a subject than the minimum magnification.
One important consideration when choosing an optical zoom system is the aperture size. The aperture is the opening in the lens that allows light to enter the camera or binoculars. A larger aperture allows more light to enter, which can result in better image quality, especially in low-light conditions.
Overall, optical zoom systems can be a great feature for capturing high-quality images and getting a closer look at distant subjects. However, it’s important to choose a system that meets your needs and budget and to keep in mind that optical zoom is just one of many factors that can affect image quality.
Single lens systems
Optical variable zoom with a single lens is a type of zoom lens design that uses a single lens element to achieve variable magnification and focal length. This type of zoom lens is commonly used in consumer cameras and mobile devices, as it provides a simple and compact solution for achieving variable magnification with minimal moving parts.
In a single-lens variable zoom system, the focal length and magnification are adjusted by moving the lens elements within the lens barrel. By changing the distance between the lens element and the image sensor or film plane, the effective focal length and magnification of the lens can be changed.
One example of a single-lens variable zoom system is the “periscope” zoom lens used in advanced smartphones. In this type of system, a single lens element is mounted at an angle within the lens barrel and is moved along its axis to achieve variable magnification. The lens element is mounted at an angle to allow for a longer effective focal length in a compact lens design.
Another example of a single-lens variable zoom system is the “Liquid Lens” zoom lens, which uses a lens element filled with a transparent fluid that can be adjusted by applying an electrical charge to the fluid. By adjusting the shape of the fluid within the lens element, the focal length and magnification of the lens can be changed.
The magnification of a system is defined by either comparing the image size to the object size or by comparing the input ray divergence to the output ray divergence. When the object is not far away, we can define the magnification as the ratio between the image and the object which is equivalent to M=-v/u{in} where u is the distance to the object and v is the distance to the image. When the object distance is infinite or very far away, the magnification is defined by the ratio between the divergence at the input compared to the divergence at the output. We will use this definition in the second exercise
Exercise 1:
- Based on the imaging condition: 1/u+1/v=1/f. and the imaging definition of M=-v/u{in}, What are the two magnifications available with a single lens which is free to move while the object and the image planes are fixed?
- Load the file “Variable_ex1.opt”.
- The distance between the sources and the image plane is 500 mm. Change the radius of the lens and place it in two places so the magnifications will be 2 and 0.5. Fill in the following table:
|
Distance between object and lens = u |
Distance between image and lens = v | Magnification | Total distance = u+v |
|
|
2 | 500 | |
|
|
0.5 | 500 | |
|
|
3 | 500 | |
|
|
0.3333 | 500 | |
Adaptive lens
Lenses that can change their curvature are known as “adaptive lenses” or “tunable lenses”. The focal length (or the refractive power) of these lenses can be modified in response to a stimulus such as an electrical signal, mechanical pressure, or temperature change. There are several types of adaptive lenses, including liquid lenses, electroactive lenses, and shape-memory alloys. Liquid lenses use a droplet of liquid that changes shape when a voltage is applied, causing the lens to change its focal length. Electroactive lenses use an electric field to change the shape of the lens, while shape-memory alloys change shape in response to temperature changes.
Adaptive lenses have a wide range of applications in various fields, such as ophthalmology, microscopy, and telecommunications. In ophthalmology, for example, adaptive lenses can be used in corrective eyewear to adjust the focus for people with presbyopia, a condition that affects the ability to focus on near objects. In microscopy, adaptive lenses can be used to correct aberrations and improve the clarity of images. In telecommunications, these can be used to control the direction and focus of light in optical communication systems.
The magnification for an object at infinite is easily calculated by evaluating the beam which passes in the middle of the lens from two different orientations. This is illustrated in Fig. 1. This beam does not deflect due to the lens, so all we need to do is to calculate the size of u_x. To change the magnification of the system, we need to shift the position of the lens and change its curvature. This is usually not a simple task since lenses are made from ridged glass, but some lenses can change their curvature easily.
Two lenses systems
Optical zoom systems with two lenses are a type of zoom lens design that uses two separate lenses to achieve variable magnification and focal length. In this type of system, one lens acts as the primary lens, while the second lens acts as a magnifying lens.
When the lens system is set to its lowest magnification, only the primary lens is used, and the magnifying lens is moved away from the primary lens. As the zoom is increased, the magnifying lens is moved closer to the primary lens, effectively increasing the magnification and focal length of the lens system.
Optical zoom systems with two lenses are commonly used in consumer cameras and camcorders, as they provide a simple and effective way to achieve variable magnification with a compact and lightweight design. They are also often less expensive than other types of zoom lenses.
One example of an optical zoom system with two lenses is the “vario” zoom lens used in compact cameras and camcorders. In this type of system, the primary lens is a fixed focal length lens, while the second lens is a magnifying lens that can be moved closer to or further away from the primary lens. As the magnifying lens moves closer to the primary lens, the magnification and focal length of the lens system increase.
Three lenses systems
An optical zoom system with three lenses typically works by using a combination of a wide-angle lens, a telephoto lens, and a zoom lens. Here is a brief explanation of how each lens works in a three-lens optical zoom system:
- Wide-Angle Lens: A wide-angle lens is designed to have a short focal length, which means it can capture a wide field of view. This lens is typically used for the minimum magnification setting in an optical zoom system, allowing you to capture a wider view of the scene. It’s also useful for landscape and architectural photography.
- Telephoto Lens: A telephoto lens is designed to have a longer focal length, which means it can magnify distant subjects. This lens is typically used for the maximum magnification setting in an Telephoto Lens: A telephoto lens is designed to have a longer focal length, which means it can magnify distant subjects. This lens is typically used for the maximum magnification setting in an optical zoom system, allowing you to get closer to distant subjects without losing image quality. It’s also useful for wildlife and sports photography.
- Zoom Lens: The zoom lens is the key component that allows you to adjust the magnification between the minimum and maximum settings. The zoom lens contains several lens elements that move back and forth inside the lens barrel to adjust the focal length and magnification of the image.
When you adjust the zoom setting on an optical zoom system with three lenses, the camera or binoculars adjust the position of the lens elements to switch between the wide-angle, telephoto, and zoom lenses as needed. This allows you to adjust the magnification of the image without sacrificing image quality. Overall, a three-lens optical zoom system can provide a versatile range of magnification options for a variety of photography and viewing needs.
Exercise 2:
Here we will analyze three lenses zoomed telescope. We will start by analyzing a regular telescope and then add a third lens. A standard telescope is based on two lenses placed at combined focal distances from each other. One lens with a long focal distance f_1 and the other with a short focal distance f_2 , as shown in Fig. 2. The telescope is intended for objects far away with parallel beams. Therefore, it enhances the angle of incoming beams. If parallel input beams are arriving at an angle \alpha_{in}, then the output angle is \alpha_{out}=f_1/f_2 \alpha_{in} .
- Load the file “Variable_ex2.opt” and run the simulation. The first lens has a focal length of 250 mm and the second lens has a focal lens of 77 mm.
- Change the angle of the source and calculate the output angle by filling in the following table:
| Input angle | Output angle |
Magnification |
|
2 |
||
|
4 |
|
|
|
6 |
|
|
|
8 |
|
|
- Now we build a telescope with variable magnification by adding a concave lens and shifting the position of the second lens. Add a concave lens with a focal length of -200 mm which changes the effective focal length of the first lens. Find the effective focal length of the first lens and the concave lens. Place the second lens according to this focal length. Find the magnification.
| Distance between the first lens and the concave lens | Effective focal length | Position of the second lens |
Magnification |
|
|
|||
|
|
|||
|
|
|||
|
|
|||
Single moving component
A variable power optical system with a single moving component refers to a type of zoom lens design that uses a single movable lens element to vary the magnification and focal length of the lens.
In this type of system, the movable lens element can be moved back and forth along the optical axis of the lens using a motor or other mechanism. This movement changes the distance between the lens elements and allows the lens to adjust its focal length and magnification.
The advantage of a variable power optical system with a single moving component is that it can provide a wide range of magnification options with fewer parts and a simpler design compared to other zoom lens designs. This can result in a smaller, lighter, and more cost-effective lens design.
One example of a variable power optical system with a single moving component is the “varifocal lens,” which is commonly used in security cameras and other applications where a wide range of magnification is needed. In a varifocal lens, a single movable lens element is used to adjust the focal length and magnification of the lens, allowing the camera to zoom in or out as needed to capture different parts of a scene.
Overall, variable power optical systems with a single moving component can provide a simple and effective solution for achieving a range of magnification options in a compact, cost-effective lens design.
Mechanically compensate zoom lens
A mechanically compensated zoom lens is a type of zoom lens that uses a combination of fixed and movable lens elements to achieve zooming while also compensating for various aberrations that can occur in the image when the lens elements move.
In a mechanically compensated zoom lens, the fixed lens elements are designed to compensate for various aberrations, such as distortion and chromatic aberration, at different zoom settings. Meanwhile, the movable lens elements are adjusted to vary the magnification and focal length of the lens.
The advantage of a mechanically compensated zoom lens is that it can provide high-quality images over a range of magnifications with minimal distortion and other aberrations. This is achieved by carefully designing the lens elements and their positions so that they work together to compensate for any aberrations that occur as the lens zooms in and out.
One example of a mechanically compensated zoom lens is the “retrofocus” design used in wide-angle lenses. In a retrofocus lens, the front element of the lens is larger than the rear element, creating a reverse telephoto configuration. This design helps to reduce the distance between the lens and the film or sensor, allowing for a wider angle of view. However, this design can also introduce various aberrations, such as distortion and chromatic aberration. To compensate for these aberrations, the lens is designed with a combination of fixed and movable lens elements, which work together to provide high-quality images over a range of magnifications.
