[center]هذه موضوع عن المجاهر الضوئية طلبها الدكتور معروف للسنة الأولى  والباقي عليكم، بالطبع البعض سيقول، من هذا المعاق الذي ينزل موضوع كهذا رداً على الدكتور، ولو كان الأمر عائداً لي لطنشت.
ولكن الدكتور ضحك عليهم وقال إن لم تأتو بالبحث سأحرمكم من فحص النظري
!!!!!!!!!!!!!!!!!!!!

microscopes
The simple microscope
General considerations

The simple microscope consists of a single or compound lens usually called a magnifier, or loupe. There are many mechanical forms in which a magnifier can be packaged to provide convenience in carrying or in use. For example, when supplied in a mount with a convenient handle, such a lens is frequently called a reading glass. A pair of lenses of low to moderate magnifying power set in a spectacle frame is often used as a magnifying aid for persons with poor vision. Higher magnification lenses are frequently packaged in a cylindrical form that can be held in place immediately in front of the eye. These are generally referred to as eye loupes or jewelers' loupes.

Basically, a simple magnifier permits the user to place his eye close to an object of interest. The closer the object is to the eye, the larger the angle that it subtends at the eye, and thus the larger the object appears. If an object is brought too close, however, the eye can no longer form a clear image. The use of the magnifying lens between the observer and the object enables the formation of a virtual image located a sufficient distance from the eye for the viewer to focus on it. To obtain the best possible image, the magnifier should be placed directly in front of the eye. The object of interest is then brought toward the eye until a clear image of the object is seen. The highest magnification will be achieved when the object is brought to the closest position at which a clear virtual image is observed. For most people, this image distance is about 25 centimetres (roughly 10 inches). As an individual ages, the nearest point of distinct vision recedes to longer distances, thus making a magnifier a useful adjunct to vision for older people.

The magnifying power, or extent to which the object being viewed appears enlarged, and the field of view, or size of the object that can be viewed, are related by the geometry of the optical system. An approximate value for the magnifying power of a lens can be found by dividing the least distance of distinct vision (25 centimetres) by the focal length of the lens. Thus, for example, a lens with a focal length of 5 centimetres will have a magnifying power of about 5 magnitudes (often written as 5×).

If the diameter of the magnifying lens is sufficient to fill or exceed the size of the eye pupil, the virtual image that is viewed will appear to be of substantially the same brightness as the original object. The field of view of the magnifier will be determined by the extent to which the magnifying lens exceeds this working diameter, as well as by the distance of the lens from the eye. The appearance of the magnified virtual image will depend upon both the aberrations present in the lens and the manner in which the lens is used.

Various aberrations influence the sharpness or quality of the image. Chromatic aberrations produce coloured fringes about the high-contrast regions of the image. Spherical aberration produces a fuzzy image. Field curvature requires users to refocus as they look over the field of view. Distortion produces curved lines from straight lines on the object. The type and degree of distortion visible is intimately related to the possible spherical aberration in the magnifier and is usually the most severe in high-power magnifiers.

The aberrations of a lens increase as the relative aperture (i.e., the working diameter divided by the focal length) of the lens is increased. Therefore, the aberrations of a lens whose diameter is twice the focal length will be worse than those of a lens whose diameter is less than the focal length. There is thus a conflict between a short focal length, which permits a high magnifying power but small field of view, and a longer focal length, which provides a lower magnifying power but a larger linear field of view.


Types of magnifiers

There are several types of magnifiers available. The choice of an optical design for a magnifier depends upon the required power and the intended application of the magnifier.

For low powers, about 2–3 magnitudes, a simple double convex lens is applicable. The image can be improved if the lens has specific nonspherical or aspheric surfaces, as can be easily obtained in a plastic molded lens. Some improvement of the distortion is easily noted when an aspheric surface is used, and the manufacture of such low-power aspheric plastic magnifiers is a major industry. In order to make the magnifier lighter in weight, a Fresnel lens can be used. A Fresnel lens, usually of embossed plastic, is in the form of a thin sheet, with the lens curvature placed in a series of concentric grooves on the surface of the sheet. This has many of the same options as a normal simple lens and can have some of the advantages of the aspheric form of the lens. The necessary presence of many symmetrical grooves on the Fresnel lens does reduce the quality of the image through light scattering, however.

For higher powers of 3–10 magnitudes, there are a number of forms for magnifiers in which the simple lens is replaced by a compound element made up of several lenses mounted and sometimes cemented together. Aspheric surfaces would be useful but are generally quite expensive to use in such compound magnifiers.

A direct improvement in the distortion that may be expected from a magnifier can be obtained by the use of two simple lenses, usually plano-convex (flat on one side, outward-curved on the other). This type of magnifier is based upon the eyepiece of the Huygenian telescope, in which the lateral chromatic aberration is corrected by spacing the elements a focal length apart. Since the imaging properties are provided and shared by two components, the spherical aberration and the distortion of the magnifier are greatly reduced over those of a simple lens of the same power.

A Coddington lens combines two lens elements into a single thick element, with a groove cut in the centre of the element to select the portion of the imaging light with the lowest aberrations. This is a simple and inexpensive design but suffers from the requirement that the working distance of the magnifier be very short.

More complex magnifiers, such as the Steinheil or Hastings forms, use three or more elements to achieve better correction for chromatic aberrations and distortion. In general, a better approach is the use of aspheric surfaces and fewer elements.


The compound microscope
General considerations

The limitation upon magnifying power imposed by the realities of the geometry of a simple magnifier can be overcome by the use of a compound microscope, in which the image is relayed by two lenses or lens systems. One lens, called the objective, has a short focal length and is placed close to the object being examined. It is used to form a real image in the front focal plane of the second lens, called an eyepiece, or ocular. The eyepiece then operates in a manner similar to that of the simple magnifier to form an enlarged virtual image that can be viewed by the observer. The magnifying power of the compound microscope is the product of the magnification of the objective lens and that of the eyepiece.

In addition to the two lenses, a basic compound microscope consists of a body tube, in which the lenses can be housed and kept an appropriate distance apart, and an illumination system, which either transmits light through or reflects light from the object being examined. Generally, some method for focusing the microscope must also be provided, as well as a means of supporting and positioning the object to be viewed.

The basic form of a compound microscope is monocular—that is, a single tube is used, with the objective at one end and a single eyepiece at the other. In order to permit viewing with two eyes and thereby increase comfort, a single objective can be employed in a tube with a binocular eyepiece on the other end. The binocular eyepiece has a matched pair of individual eyepiece lenses; beam-splitting prisms are used to send half of the light from the image formed by the objective to each eye. These prisms are mounted in a rotating mechanical assembly so that the separation between the eyepieces can be made to match the required interpupillary distance for the observer. (A stereoscopic microscope is configured by using two objectives and two eyepieces, enabling each eye to view the object separately, making it appear three-dimensional.)


Optics

There are some obvious geometric limitations that apply to the design of microscope optics. The attainable resolution, or the smallest distance at which two points can be seen as separate, or resolved, when viewed through the microscope, is the first important property. This is generally set by the ability of the eye to discern detail, as well as by the basic physics of image formation.

The eye's ability to ascertain detail is in turn determined by several parameters, including the level of illumination and the degree of contrast between light and dark regions on the object. Under reasonable light conditions, a normal eye with good visual acuity is capable of seeing two high-contrast points if they subtend a visual angle of at least one arc minute in size. Thus, at a nominal viewing distance of 25 centimetres, the points must be at least 0.1 millimetre apart or the eye will not be able to see them as separate. With a simple magnifier of 10 power, an observer can see two points separated by perhaps 0.01 millimetre. With a compound microscope of 100 power, one might expect the observer to be able to distinguish two points only 0.001 millimetre apart, but an additional complication arises for the high magnifications encountered in a compound microscope. When the dimensions to be resolved approach the wavelength of light, consideration must be given to the effect of diffraction upon the eye's ability to resolve details upon objects (see below The theory of image formation).

The resolution and the light-collecting capability of the microscope are determined by the numerical aperture of the objective. The numerical aperture is defined as the sine of half the angle of the cone of light from each point of the object that can be accepted by the objective multiplied by the index of refraction of the medium in which the object is immersed. Thus, the numerical aperture increases as the lens becomes larger or the refractive index increases. Typical values for microscope objective numerical apertures range from 0.1 for low-magnification objectives to 0.95 for dry objectives and 1.4 for immersed objectives. A dry objective is one that works with the object in air. An immersion objective requires using a liquid, usually a transparent oil, to fill the space between the object and the first element of the objective.

The limit of resolution is set by the wavelength of light and the numerical aperture. The resolution can be improved either by increasing the numerical aperture of a lens or by using light with a shorter wavelength. In an immersion objective, the effective wavelength of the light is reduced by the index of refraction of the media within which the object being examined resides. The use of immersion imaging techniques in microscopy improves the resolution capabilities of the microscope.


Mechanical components

The microscope tube separates the objective and the eyepiece and assures continuous alignment of the optics. It is a standardized length, which permits objectives and eyepieces of different powers to be interchanged with the assurance that the image quality will be maintained. Traditionally this length has been defined from the end of the screw thread that attaches the objective to the tube to a specific location at the eyepiece end of the tube. A standard length of 160 millimetres was accepted for most uses, and of 250 millimetres for metallographic microscopes. Most microscope objectives are designed to minimize aberrations at one of these distances. Use of other distances will affect the aberration balance for high-magnification objectives. Therefore, focusing of the traditional microscope requires moving the objective, the tube, and the eyepiece as a rigid unit. To achieve this, the entire tube is fitted with a rack-and-pinion mechanism that allows it, together with the objective and the eyepiece, to be moved toward or away from the specimen as needed.

The specimen in question is usually mounted on a glass slide and placed on the microscope stage (located directly below the objective). The stage is generally supplied with a pair of knobs featuring a rack-and-pinion arrangement. This permits the glass slide to be moved across the stage in two directions so that different areas of the specimen can be examined.

The accuracy with which the focusing and the movement of the slide have to be maintained increases as the depth of focus of the objective decreases. For high-numerical-aperture objectives, this depth of focus can be as small as one or two micrometres, which means that the mechanical components must provide stable motion at even smaller increments.

Several approaches have been introduced to achieve such precise stable motion at reasonable cost. Some designers have eliminated the sliding mechanism of the body tube, incorporating adjustments for the vertical movement needed for focusing, as well as the lateral motion of the object, in a single mechanical system. A more common approach has been to mount a relay objective doublet of 160-millimetre focal length into the lower end of the tube. This tube lens is attached to the tube in a fixed position and is designed to accept light from an image relayed by the objective to an infinite distance. The microscope objective itself is then designed to have aberrations corrected for an infinite object distance. An advantage of this approach is that, since the relayed image is at infinity, the microscope objective itself, a very lightweight component, can be moved to effect focusing without upsetting the aberration balance.

Because users of a microscope often desire the ability to choose between objectives of several different magnifications in order to suit the magnification to the requirements of the object, some microscopes are equipped with readily interchangeable nosepieces carrying different objectives. Others feature a rotating nosepiece that carries several objectives in a turret. In many cases, the eyepiece is designed as a portion of a zoom lens, which permits continuous variation of the magnification over a limited range.


The illumination system

The illumination system of the standard optical microscope is designed to transmit light through a translucent object for viewing. In a modern microscope, it consists of a light source, usually an electric lamp of some form, and a lens or lens system known as a condenser. The condenser concentrates the light, providing bright, uniform illumination in the region of the object under observation. Typically, the condenser focuses the image of the light source directly onto the plane of the specimen, a technique called critical illumination, or the image of the source is focused onto the condenser, which is then focused onto the entrance pupil of the microscope objective, a process called Köhler illumination. The advantage of the latter approach is that nonuniformities in the source are averaged in the imaging process. To obtain optimum use of the microscope, it is important that the light from the source both cover the object and fill the entrance aperture of the objective of the microscope. Usually, the quality of the image formation from the condenser is not critical, as it is primarily intended to provide uniform illumination. There are applications, such as phase-contrast imaging, where the quality of the source image is important, however.


The objective

The optics of the microscope objective are defined by the focal length, numerical aperture, and field of view. Objectives that have been corrected for aberrations are further defined by the wavelength requirements and the tube length of the microscope.

Manufacturers provide objective lenses with standard magnifications ranging from 2× to 100×. The focal length of the objective is inversely proportional to the magnification and, in the majority of modern microscopes, equals the tube length (usually 160 millimetres) divided by the magnification. The field of view of the eyepiece is usually set to be a standard size of about 20-millimetre diameter. The field of view of the objective is then set to range from 10 millimetres for an objective with a magnifying power of 2× to 0.2 millimetres for an objective with a magnification of 100×. As a result, the angular field of view is about a total of 7° for all objectives.


Aberration correction

The numerical aperture and the complexity of the objective increase as the magnification increases. Low-power objectives, of the order of two to five magnitudes, are generally simple two-element, or doublet, lenses. Ordinary crown glass and flint glass (optical glasses with, respectively, low and high refractive indexes) can be used to obtain correction for the spherical aberration and chromatic aberration.

For objectives with magnifying powers of 10×, the required numerical aperture increases to 0.25, and a more complex type of lens is required. Most microscope objectives of this magnification use a separated pair of doublets, sharing the refractive power. The correction of spherical aberration is readily achieved, but residual chromatic aberration is obtained when normal optical glasses are used for the lens elements. For most optical applications, this is not important. For the critical high-magnification microscope objectives (magnifications greater than 25×), this aberration is visible as chromatic blur. The only method of correcting this residual aberration is through the use of special optical glasses whose dispersion properties vary from the normal glasses. There are only a few such glasses or crystalline materials that are useful for this purpose. Objectives designed using these special glasses are called apochromats.

Most traditional microscope objectives do not produce a flat image surface. The intrinsic field curvature is generally of little importance in the visual use of the microscope because the eye has a reasonable accommodative capability when examining the image. Field curvature is, however, a problem for video or photographic systems. Special objectives with flat-field lenses have been designed for these purposes.


High-power objectives

High-power objectives pose several design problems. Because the focal length of an objective decreases as the numerical aperture and magnifying power increase, the working distance, or distance from the objective to the object, is shortened for higher-power objectives. The need to use additional elements in the lens system for high magnifications further shortens the working distance to only 10 to 20 percent of the focal length. Thus, an objective with a magnification of 40× and a focal length of 4 millimetres may have a working distance of less than 0.4 millimetre, which clearly becomes a problem. A number of objectives with increased working distance have been designed. These use a negative lens element between the object and the eyepiece, which has the added attraction of providing some field flattening as well. These objectives are especially of value in use with video detectors.

In objectives with magnifying powers of 25× or greater, meniscus-shaped aplanatic elements are designed into the microscope objective in the space between the object and the pairs of doublets that carry out the relayed imaging. These aplanatic components have the optical property of converging the light without adding spherical aberration to the image and are important in that they provide some increase in the numerical aperture without introducing considerable additional aberration.

The highest-power microscope objective available is the immersion objective. When this type of objective is used, a drop of oil must be placed between the object on the microscope slide and the bottom of the objective. The objective is then moved toward the slide until it contacts the drop of oil, capturing a region of oil between the slide and the objective. The oil used typically has an index of refraction which matches that of the glass in the first component of the objective and which is greater than that of air. Increasing the refractive index in this way increases the numerical aperture, thus permitting higher magnifications. The first component used in immersion objectives is generally a hyper-hemisphere (a small optical surface shaped like a hemisphere but with a bounding curve exceeding 180 degrees), which acts as an aplanatic coupler between the slide and the rest of the microscope objective. An immersion objective with a high numerical aperture typically consists of a hyper-hemisphere followed by one or two aplanatic collectors and then two or more sets of doublets. Such objectives are made with magnifying powers greater than 50×, the extreme being about 100×.


Depth of focus

The large numerical aperture of most microscope objectives severely restricts the focusing requirements of the objective. The depth of focus is shown in the table as the accuracy with which the focal plane must be located in a direction along the axis of the microscope optics in order that the highest possible resolution can be obtained.



The eyepiece

The eyepiece is selected to examine the relayed image under conditions that are comfortable for the viewer. The magnifying power of the eyepiece generally does not exceed 10×. The field of view is then about 40° total, a convenient value for a relatively simple optical design. The observer must place his eye in the exit pupil of the eyepiece, the point at which the light rays leaving the eyepiece come together. In most cases an eye relief (or distance from the exit pupil to the last element of the eyepiece) of about one centimetre is desirable. Too short an eye relief makes viewing difficult for observers who wear corrective eyeglasses.

All the objectives described above are nominally intended to relay an image through an eyepiece for direct viewing by an observer. The use of a photographic recording method requires that a real image be provided to a film holder or camera without a lens. One approach is to remove the eyepiece and place the film holder directly in the focal plane of the eyepiece and thus intercept the image from the objective directly. A better approach is to use a specifically designed projection eyepiece, which can be adjusted to provide the appropriate magnification coupling the image to the film. Such an eyepiece can incorporate a change in the chromatic aberration correction to accommodate the requirements of the photographic system.

Even more prevalent today is the use of an electronic detector to capture the magnified image as a video signal. This video signal can be observed directly on a monitor or sent to a computer via a frame “grabber” that captures a single frame (or perhaps several averaged frames) of video data. The computer can then be used to provide some image processing.


The theory of image formation

The geometric optics of image formation in the compound microscope are easy to understand. The objective collects a fan of rays from each object point and images the ray bundle to the front focal plane of the eyepiece. All the rules of ray tracing apply to the image formation. In the absence of aberration, geometric rays form a point image of each object point. In the presence of aberrations, each object point is represented by a blurred point. The eyepiece images the rays to a focal point at a convenient distance for viewing the image. In this direct view approach, the brightness of the image is determined by the sizes of the apertures of the lenses and by the size of the pupil of the eye. The focal length and resulting magnification of the objective should be chosen to attain the desired resolution of the object at a size convenient for viewing with the eyepiece.

The actual image formation in the microscope is complicated by the diffraction and interference that take place in the imaging system and by the requirement to use a light source that is imaged into the focal plane.

The modern theory of image formation in the microscope was initiated by the German physicist Ernst Abbe in 1873. The starting point for the Abbe theory is that objects in the focal plane of the microscope are illuminated by convergent light from a condenser. The convergent light from the source can be considered as a collection of many plane waves propagating in a specified set of directions and superimposed to form the incident illumination. Each of these effective plane waves is diffracted by the details in the object plane: the smaller the detail structure of the object, the wider the angle of diffraction.

The structure of the object can be represented as a sum of sinusoidal components. The rapidity of variation in space of the components is defined by the period of each component, or the distance between adjacent peaks in the sinusoidal function. The spatial frequency is the reciprocal of the period. The finer the details, the higher the required spatial frequency of the components representing the object detail. Each spatial frequency component produces diffraction at a specific angle dependent upon the wavelength of light. For example, spatial frequency components having a period of one micrometre would have a spatial frequency of 1,000 lines per millimetre. The angle of diffraction for such a component for visible light with a wavelength of 550 nanometres will be 33.6°.

The microscope objective collects these diffracted waves and directs them to an image plane, where interference between the diffracted waves produces an image of the object. Because the aperture, of the objective is limited in size, not all the diffracted waves from the object can be transmitted by the objective. Abbe showed that the greater the number of diffracted waves reaching the objective, the finer the detail that can be reconstructed in the image. He designated the term numerical aperture as the measure of the objective's ability to collect diffracted light and thus also of its resolving power. On this basis, it is obvious that the greater the magnification of the objective, the greater the required numerical aperture of the objective. The largest numerical aperture theoretically possible in air is 1.0, but practical optical design questions limit the largest achievable numerical aperture to 0.95 or less.

For the example above of a component with a spatial frequency of 1,000 lines per millimetre, the required numerical aperture to collect the diffracted light would be 0.55. Thus, an objective of 0.55 numerical aperture or greater must be used to observe and collect useful data from an object with details spaced one micrometre apart. If the objective has a lower numerical aperture, the details of the object will not be resolved. Attempts to enlarge the image detail by use of a high-power eyepiece will yield no more useful resolution. This latter condition is called empty magnification.

For resolving the smallest possible details, it is possible to use the principle that the wavelength of light is shortened when propagating through a dense medium. This explains why immersion objectives are able to collect light diffracted by smaller details than can dry objectives. The numerical aperture is multiplied by the index of refraction of the medium, and working numerical apertures of 1.25 to 1.4 are possible. At the extreme, spatial frequency components with periods as small as 0.4 micrometre can be observed.


Specialized types of microscopes
Stereoscopic microscopes

Binocular stereomicroscopes are, fundamentally, a matched pair of microscopes mounted side by side, usually with a small angle between the optical axes. The object is imaged independently to each eye, and the stereoscopic effect, which permits discrimination of height on the object, is retained. The effect can be exaggerated by proper choice of the design parameters for the microscopes. For practical reasons, the magnifying power of such instruments is usually in the range of 5 to 50 magnitudes. These microscopes are important in any work in which fine adjustment of tools or devices is to be made. For example, much use of the stereomicroscope is made in biological laboratories for dissection of subjects and in the operating room for microsurgical procedures. Moderate-power stereomicroscopes are even more widely used in the electronics manufacturing industry, where they enable human workers, as well as computer-controlled machines, to bond leads to tiny integrated-circuit chips.

شكرا يا Iron man على هالمبادرة اللطيفة و عنجد كلك ذوق.
بس يمكن محمد معروف طالب معلومات كمان.
ما بعرف ليش هالدكتور معقد الأمور كتير
لسا ما أخدنا غير 3 محاضرات و صرنا خالصين 60% من الكتاب
و عنجد شكراً كتير ألك مرة تانية    

عطي هدلول وألف خير
لأن يعني مهما دورت بظن ما رح تلاقي أكثر من هالشي
بس فعلاً معروف "................."
فلا يهمك وطنشوه
لأنه  ما يطلع بإيده شي

طيب حدها اتفقوا على ترجمتها
يعني تعاون
وبظن أنو هي بتكفي وبتوفي
لأن ما بظن في معلومات أكتر من هيك
؟؟؟؟؟؟؟؟؟

بس حبيت قلك أنو صار كل طلاب السنة الأولى ينسخو نفس يلي حاطو
عالمنتدى ، يعني صار الكل عندو نفس البحث


مشان هيك صارت العلامة تبع البحث (خمس علامات من أصل 30 تبع العملي )تنحط عأساس التنسيق و التجليد و التلوين و ما عادوا انتبهوا عالمعلومات يلي مكتوبة


بقى ما راحيت غير علينا نحنا الكم واحد يلي قعدوا ساعات يدورو عالانترنت و آخر شي ما حدا قرأ شو كاتبين و أخدوا علامة حسب التنسيق و بس

هالدكتور بوادي والمادة بوادي وأنا بوادي مع هيك مابتوقع يكتفي بالمعلومات المنشورة لأنو حضرتو طالب 3 صفحات على الأقل عن كل واحد        

بس أنا حكولي الطالبات الي داومه أنه البحث عن المجاهر للدكتورة ميساء (للعملي) مو للدكتور معروف هم هيكـ حكولي أنا ما كنت مداومه لسه ..
و البحث إذا كان الدكتور هو الي طلبه طلبه بحث عن المجاهر ما عدا (الضوئي و الالكتروني) بس بهاي الحالة عن ش احنا بدنا نبحث لكن ؟؟

بدي شرح عربي لمجاهر برايت فيلد للعينات الملونة و برايت فيلد للعينات غير ملونة و الفلورة و الطور المعكوس ونورماسكي و كونفوكال

اي شي يعبي تلات  صفحات
رجاء زملاء

شكرا كتير عالموضوع   بس الدكتور  طلب الحديث عن أنواع المجاهر ماعدا الإلكتروني والضوئي شو بتصحونا نعمل  وين بدنا نلاقي هيك شي

شباب صبايا انا عجزت وانا عم دور بالنت على هالموضوع وما لقيت الشي اللي بدو ايا الدكتور لا وفي مجهرين الانترنت نفسه مو سمعان فيهم!   مشان الله حدا لقى شى؟