S-polarized light is reflected differently compared to p-polarized light, especially at angles far from normal incidence. These differences are exploited in ...

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).

The idea behind such a construction is quite clear. The samples for an inverted microscope are positioned in a petri dish, a flask or any other “high volume” vessel. Adherend cells at the bottom of the vessel have to be treated with an objective of 1.1mm cover slip correction (in this case the bottom of the vessel is equivalent to the cover slip). Floating cells or water samples from a pond need the additional LWD feature. Only this construction allows a focusing “through” the sample, inspecting the complete fluid layer. A short look on motorized inverted microscopes gives us an interesting hint: Before changing the objective by rotating the nosepiece, first drive down the revolving nosepiece. This will avoid scratches on the front lens. Parfocality of the objectives in this case is less relevant.

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.

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.

For “dry” objectives with high numerical apertures (≥ 0.7) it is helpful to use cover slips with a minimized tolerance in thickness. The lab suppliers offer glasses with a tolerance of +/- 0.005mm. Together with a “flat” embedding of the sample, preconditions for a good image result are given.

The cover slip has to be placed on top of the sample. A slight pressing of a dissecting needle will help to avoid too much embedding medium (water, etc.) between sample and cover slip. The embedding medium in this case works as an additional layer and thus simulates a thicker cover slip. A wrong covering of the sample reduces the N.A. power, means detail information and contrast. So please take care to mount your section properly.

Stagemicroscope function

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]

High power objectivemicroscope function

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Besides performing the first step of magnification in a compound microscope, means following an imaging purpose, in incident light applications for uncovered specimen this kind of objectives is also used for illumination purposes. Traced from the light source, the light passes these objectives on its way to the sample, thus requesting another kind of anti-reflex coating within the objective. A typical setup for that kind of samples looks like this:

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Types ofmicroscope objectives

2. In some medical work flows it is common to omit the covering of the sample. In this case Non-Cover-Glass objectives without cover slip correction are necessary, especially for objectives with an N.A. ≥ 0.30. The higher the N.A., the more the correct objective (0.17 vs. 0) has an influence on the image quality. Non-covered blood smears are typical samples.

Low power objectivemicroscope function

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8. For Inverted Microscopes in bio/medical applications, especially higher magnifications need a Long-Working-Distance construction. The LWD feature works of course at the expense of resolution power.

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.

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Condensermicroscope function

6. Following another international coding, Phase Contrast objectives are marked with a green inscription. Phase contrast is a contrast method for transmitted light, but the respective objectives can also be used in bright field. A slight reduction of image quality is system immanent.

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.

4. For maximum resolution power, immersion objectives are the best option. Mostly it is immersion oil with a defined refractive index (1,51) to be in use, but please realize that water or glycerin in some cases are preferred. The necessary immersion medium is indicated on the objective sleeve. Immersion for that kind of objectives is not an option, it is an imperative!

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.

Stage clipsmicroscope function

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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.

7. For metallurgical applications, dark field (DF) in incident light is quite common. The necessary objectives have to have a larger diameter to incorporate the DF illumination ring: a mirror system built around the centrally positioned bright field objective. Analog to the situation in transmitted light, a central stop in the Epi illuminator (some people call this device Epi condenser!) stops the direct light entering the objective. So the periphery of such an objective works as an illuminator, the central part as an imager.

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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 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.

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.

Armmicroscope function

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×.

Ocular lensmicroscope function

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.

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.

Different samples require different microscopes. This rule refers to the fact that an opaque, bulky sample with a reflective surface needs another treatment than a transparent, unstained smear from the cavitas oris. The microscope stand offers the necessary space for a correct positioning of the sample and all options for the appropriate illumination method.The microscope objective is an even more specific item. Here we talk about the required resolution power (= numerical aperture), but also about cover glass correction, immersion method and working distance.1. The standard upright microscope for transmitted light is constructed for glass slides with a 0.17mm cover slip. This restriction is indicated on the objective sleeve:

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.

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 (∞).

5. Objectives for Polarization Microscopes just have one purpose. Here we do not talk about color fidelity (in any case Plan Apos will be best) or transmission rates (Fluorite objectives with a reasonable quantity of glass built in are mostly recommended). Here we talk about strain-free glass elements mounted without tension within the objective. Once this target is achieved, the purpose of these objectives is fulfilled: maximum extinction when polarizer and analyzer are crossed.

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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]