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In a telescope the objective is the lens at the front end of a refracting telescope (such as binoculars or telescopic sights) or the image-forming primary mirror of a reflecting or catadioptric telescope. A telescope's light-gathering power and angular resolution are both directly related to the diameter (or "aperture") of its objective lens or mirror. The larger the objective, the brighter the objects will appear and the more detail it can resolve.

The start of the development of plastic optical fiber for communication (POF for short) is almost the same as that of glass optical fiber, both of which started in the 1960s.

A typical microscope has three or four objective lenses with different magnifications, screwed into a circular "nosepiece" which may be rotated to select the required lens. These lenses are often color coded for easier use. The least powerful lens is called the scanning objective lens, and is typically a 4× objective. The second lens is referred to as the small objective lens and is typically a 10× lens. The most powerful lens out of the three is referred to as the large objective lens and is typically 40–100×.

Historically, microscopes were nearly universally designed with a finite mechanical tube length, which is the distance the light traveled in the microscope from the objective to the eyepiece. The Royal Microscopical Society standard is 160 millimeters, whereas Leitz often used 170 millimeters. 180 millimeter tube length objectives are also fairly common. Using an objective and microscope that were designed for different tube lengths will result in spherical aberration.

Particularly in biological applications, samples are usually observed under a glass cover slip, which introduces distortions to the image. Objectives which are designed to be used with such cover slips will correct for these distortions, and typically have the thickness of the cover slip they are designed to work with written on the side of the objective (typically 0.17 mm).

If these scenarios use GI plastic fiber, it may be more conducive to user operation and maintenance, and the cost is also lower. But unfortunately, there is no domestic production of GI plastic optical fiber, the international GI plastic optical fiber industry is not perfect, plastic optical fiber in the scale of communication applications also become distant.

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One of the most important properties of microscope objectives is their magnification. The magnification typically ranges from 4× to 100×. It is combined with the magnification of the eyepiece to determine the overall magnification of the microscope; a 4× objective with a 10× eyepiece produces an image that is 40 times the size of the object.

The figure below shows plastic optical fibers with different core diameters, the transparent part of the fiber in the figure is the core/cladding, and the black sheath is the tight sleeve layer. At the same time, plastic optical fiber is relatively soft, optical fiber can be truncated with a simple tool, and fiber ends can be completed manually. Figure a below shows the blade for cutting plastic optical fiber, and figure b below shows several plastic optical fiber connectors. The termination of glass optical fiber is much more troublesome. For example, in the FTTR scenario, the core diameter of the fiber in the indoor cable is only about 10 μm, and the cutting and termination of the indoor cable requires the operator to arrange for special technicians and equip the fiber fusion splicer to complete. If the use of GI plastic fiber, the user’s home fiber optic cabling, cutting, termination and other work can be completed by the user.

GI plastic fiber has less attenuation and large bandwidth. The mode bandwidth of some models of GI plastic optical fiber is up to 10Gbps-100m, which can support 10Gbps transmission within 100m, and can work at 850nm and 1300nm wavelengths, which can be used in most scenarios as an alternative to OM1, OM2, and OM3 multimode fibers.

All these types of objectives will exhibit some spherical aberration. While the center of the image will be in focus, the edges will be slightly blurry. When this aberration is corrected, the objective is called a "plan" objective, and has a flat image across the field of view.

The distinction between objectives designed for use with or without cover slides is important for high numerical aperture (high magnification) lenses, but makes little difference for low magnification objectives.

At present, the country only has the production capacity of SI plastic optical fiber, plastic optical fiber is only used in industrial control, automotive multimedia and other low-speed systems.

The traditional screw thread used to attach the objective to the microscope was standardized by the Royal Microscopical Society in 1858.[3] It was based on the British Standard Whitworth, with a 0.8 inch diameter and 36 threads per inch. This "RMS thread" or "society thread" is still in common use today. Alternatively, some objective manufacturers use designs based on ISO metric screw thread such as M26 × 0.75 and M25 × 0.75.

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The drawing process is just a densification process from thick rod to fine fiber, and the transmission properties of the fiber need to be obtained through the rod-making process. Therefore, GI plastic optical fiber manufacturing difficulties is to create a core refractive index distribution in line with below figure of the perform rod. The process of wire drawing from the preform is shown in the figure below. In some university laboratories, plastic optical fibers for testing are manufactured by the drawing method.

With high attenuation and low bandwidth, SI plastic optical fiber is suitable for short-distance communication systems with a transmission distance of not more than 100 meters and a transmission rate of not more than 100 Mbps.

There are two main ways to manufacture plastic optical fiber, extrusion method and drawing method. SI plastic optical fiber is usually produced by extrusion method and GI plastic optical fiber is mainly produced by drawing method.

Communication poles, also known as electric poles or telegraph poles, are supporting structures in power or communication line systems. They are usually made of wood, reinforced concrete or other materials

Back focal planeofobjective lens

SI Plastic Fiber Extrusion Production Line usually consists of a granule drum, transfer pump, core extruder, cladding extruder and fiber tray, as shown in the figure below.

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In FTTR, in-building wiring and other scenarios that require high transmission rates, glass fiber or twisted pair cable is still used as the transmission medium.

Microscope

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Instead of finite tube lengths, modern microscopes are often designed to use infinity correction instead, a technique in microscopy whereby the light coming out of the objective lens is focused at infinity.[1] This is denoted on the objective with the infinity symbol (∞).

Camera lenses (usually referred to as "photographic objectives" instead of simply "objectives"[4]) need to cover a large focal plane so are made up of a number of optical lens elements to correct optical aberrations. Image projectors (such as video, movie, and slide projectors) use objective lenses that simply reverse the function of a camera lens, with lenses designed to cover a large image plane and project it at a distance onto another surface.[5]

The objective lens of a microscope is the one at the bottom near the sample. At its simplest, it is a very high-powered magnifying glass, with very short focal length. This is brought very close to the specimen being examined so that the light from the specimen comes to a focus inside the microscope tube. The objective itself is usually a cylinder containing one or more lenses that are typically made of glass; its function is to collect light from the sample.

Numerical aperture for microscope lenses typically ranges from 0.10 to 1.25, corresponding to focal lengths of about 40 mm to 2 mm, respectively.

The refractive index of the core of a GI fiber is variable, and the speed of light transmitted along different paths is also variable. Although the path along the fiber core is the shortest, it has the highest refractive index, so the light travels the slowest; the farther away from the core, the smaller the refractive index, and the faster the light travels there.

The production process is that the pellets as the core are put into the granule drum, and then they are injected into the core extruder to extrude the core by using the transfer pump, and then the cladding extruder is used to extrude a cladding on the outside of the formed core, and then it is cooled quickly, and then finally it is made into the SI plastic optical fiber.

By using the transmission speed difference and the transmission optical range difference to completely cancel each other, dispersion can be eliminated, thus increasing the bandwidth of the GI fiber. The transmission of light in SI and GI fibers is shown below. There are two main core/cladding materials for plastic optical fibers, PMMA (polymethylmethacrylate) and PF-PMMA (fluorinated PMMA).

Objective lens

The advantage of plastic optical fiber is good flexibility and strong bending resistance, therefore, the core diameter of plastic optical fiber can be made larger, so that the coupling between the optical fiber and the light source will be easier.

Basic glass lenses will typically result in significant and unacceptable chromatic aberration. Therefore, most objectives have some kind of correction to allow multiple colors to focus at the same point. The easiest correction is an achromatic lens, which uses a combination of crown glass and flint glass to bring two colors into focus. Achromatic objectives are a typical standard design.

Plastic optical fiber attenuation, low bandwidth, easy to become the end of the characteristics of the plastic optical fiber is suitable for short distances, the transmission rate requirements of the scene is not high.

In optical engineering, an objective is an optical element that gathers light from an object being observed and focuses the light rays from it to produce a real image of the object. Objectives can be a single lens or mirror, or combinations of several optical elements. They are used in microscopes, binoculars, telescopes, cameras, slide projectors, CD players and many other optical instruments. Objectives are also called object lenses, object glasses, or objective glasses.

PF-PMMA (fluorinated PMMA) has a small attenuation coefficient but is more expensive and is generally used in GI plastic fibers.

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How to usemicroscope

When it comes to the classification of optical fiber for communication, it is relatively easy to think of: multi-mode fiber, single-mode fiber, G.652, G.654, etc. But from the 1970s, the development of glass optical fiber is like a hang-up, while the plastic optical fiber has been difficult to solve because of the problem of attenuation to the point that it is difficult to find its trace in the communication network.

In addition to oxide glasses, fluorite lenses are often used in specialty applications. These fluorite or semi-apochromat objectives deal with color better than achromatic objectives. To reduce aberration even further, more complex designs such as apochromat and superachromat objectives are also used.

The working distance (sometimes abbreviated WD) is the distance between the sample and the objective. As magnification increases, working distances generally shrinks. When space is needed, special long working distance objectives can be used.

The attenuation coefficient of plastic optical fiber is shown below. Plastic optical fiber belongs to class A4 multimode fiber, which is divided into several subclasses. The main transmission characteristics of different subclasses of SI plastic optical fiber are shown in Table 1, where the values refer to the typical values of current products. The main transmission characteristics of different subclasses of GI plastic optical fiber are shown in Table 2. Since GI plastic optical fiber is less used in China, the values in the table are mainly quoted from IEC 60793-2-40:2021, and the mode bandwidths of the actual products are higher than those in Table 2, such as the mode bandwidths of a certain A4h class of products up to 9700Mhz-100m.

At present, the domestic plastic optical fiber manufacturers only have the production capacity of SI plastic optical fiber, which are produced by extrusion method. The picture below shows the extruder and fiber tray of the plastic optical fiber being produced. The drawing method requires the use of chemical methods to create the designed refractive index distribution of the large-diameter perform rod, and then the perform rod are placed in a high-temperature furnace, heated to make it soften and drawn to meet the diameter requirements of the fine optical fiber.

Which objective lens should beinposition before you store amicroscope

Depending on the refractive index distribution of the core, plastic optical fibers are classified into step index (SI) and gradient index (GI) fibers. The refractive index distribution of SI and GI fibers is shown in the figure below. In SI fiber, different rays of light travel along paths of different lengths, and when they reach the output of the fiber they become discrete in time, with instantaneous delay, which affects the bandwidth.

G.657 optical fiber is also known as bending loss insensitive optical fiber. The optical cable that is thinner than ordinary telephone lines used to connect FTTH uses G.657 optical fiber.

Some microscopes use an oil-immersion or water-immersion lens, which can have magnification greater than 100, and numerical aperture greater than 1. These objectives are specially designed for use with refractive index matching oil or water, which must fill the gap between the front element and the object. These lenses give greater resolution at high magnification. Numerical apertures as high as 1.6 can be achieved with oil immersion.[2]