Comparison Levenhuk 870T vs Levenhuk 850B

Research methods applicable to this microscope model.

— Bright field. The most famous and widely used method of light microscopy. The object under consideration in such studies is placed on a light background, against which it looks darker. Note that different methods of illumination can be used for research: direct through, oblique, reflected. The first option (when the light from a lamp or a mirror under the stage shines through the sample) is optimal for studying transparent samples, the key details of which are darker than the general background. Typical examples are thin sections of animal and plant tissues. Oblique light is similar in application specifics, while it gives a grey background and is inferior to direct light in terms of backlight efficiency, but provides a more embossed image. As for reflected light, in this case it is indispensable when examining opaque objects: samples of ores and other materials, semiconductor wafers, etc. Anyway, bright-field microscopy well reveals, first of all, details that are noticeably different in light transmission or refractive index from the surrounding background (with through illumination), or give noticeable reflections / shadows (with reflected light).

— Dark field. A kind of opposite of bright-field research: the object under consideration or its individual elements are lighter than the surrounding background. However, this is not just a “negative” of the image, but a separate method with its own c...haracteristics. Illumination in dark-field microscopy is usually through, but it is carried out in a specific way: the middle of the light beam is blocked by a hood, and the light “cylinder”, passing through the condenser lens, turns into an “hourglass”. At the same time, in the narrowest place of such a "clock" there is a preparation, and towards the lens, the light cone expands so that it does not fall into the optics. Thus, the user sees in the microscope only the light scattered by the preparation and the dark background around. This method of research, among other things, allows you to identify "smooth" details that do not stand out sharply against the surrounding background and are not visible in a bright-field study. Among the applications of dark-field microscopy are the work with unstained biological preparations (cells, tissue samples, microorganisms), as well as the study of some transparent materials for small surface defects.

— Phase contrast. A method used to study transparent and colourless objects with an inhomogeneous structure, used when this inhomogeneity cannot be detected by more traditional bright-field microscopy. The idea of this method is that when passing through structures with different refractive indices, light receives different phase changes. These changes are not visible with ordinary optics, but they can be made visible with the help of special equipment — namely, a condenser and a lens of a special design. Accordingly, such equipment is necessarily included in the scope of delivery of the microscope.

— Fluorescent. This method provides the illumination of observed objects with light of a certain wavelength, under the influence of which these objects or their individual elements begin to glow, while the background remains dark. If necessary, coloring substances are introduced into the preparation to improve luminosity (a typical example is biological objects, most of which fluoresce rather weakly by themselves). For illumination, usually, UV radiation is used, therefore this method is also called ultraviolet microscopy; The image enters the eyepiece of the microscope through a filter that filters out UV rays, but freely passes the visible glow of the drug.
One of the main features of fluorescence microscopy is high resolution: it allows you to clearly see even very small objects that are not visible in the usual visible range. In fact, this method in terms of resolution is between classical optical and electron microscopy; At the same time, in contrast to electron and atomic microscopes, devices with the support of the UV method make it possible to examine even the hardware of living cells and microorganisms. And some special variants of this technique make it possible to achieve not micro, but nanoscopic magnifications. The second popular use of fluorescence microscopy is the detection of particles, elements, inclusions, etc., which are not visible under ordinary light, but stand out well in ultraviolet light. A typical example is the surface of many metals and alloys.

— Monocular. An eyepiece with a single lens that can only be viewed with one eye. For obvious reasons, it is only used in biological microscopes (see "Type"). The advantages of monoculars are primarily smaller size and cost than other varieties; in addition, they do not require adjustment for interpupillary distance. On the other hand, constantly looking into the eyepiece with one eye is tiring, so this option is poorly suited for situations where you have to look into the microscope often and for a long time.

— Binocular. Dual eyepiece that can be viewed with both eyes at once. Note that such optics are used not only in stereomicroscopes, originally intended for viewing an object through two lenses (see "Type"), but also in biological microscopes with one lens. The fact is that looking into an optical device with two eyes is much more convenient than with one, while the eyes are less loaded and fatigue does not occur so quickly. Therefore, for serious tasks associated with frequent use of a microscope, binoculars (or trinoculars, see below) are the best option. Such optics cost more than monocular, but this is offset by ease of use.

— Trinocular. A kind of binocular (see the relevant paragraph), supplemented by a third optical channel for a special camera-video eyepiece. Such a camera is usually connected to a PC or laptop; by installing it i...n the socket for the third eyepiece, you can take photos and videos, as well as display the image in real time on the computer screen. At the same time, you can look through the microscope in the usual way. Devices with trinoculars are very functional and versatile, but they are complex and expensive.

— LCD screen. The microscope has an LCD screen that replaces the traditional eyepiece. You do not need to bend over to such a device each time to view the image, which is very convenient if observations need to be combined with record keeping and other similar activities. Microscopes of this design usually have a photo and video function, as well as various built-in tools — for example, a scale grid for estimating the size of visible objects, displayed directly on the screen. In addition, the image on the screen can be seen not only by the direct user, but also by everyone who is nearby; such features are indispensable during training sessions, consultations, presentations, etc. On the other hand, such microscopes turn out to be bulky and expensive.

— magnification factor. The magnification provided by the eyepiece. This parameter, along with the lens magnification, affects the overall magnification of the device (see above). The classic option for eyepieces in microscopes is 10x, but higher values \u200b\u200bare also found. The package may include several eyepieces, of different magnification — to change the overall degree of magnification. There is a multiplicity designation with a letter index, for example, WF10x. This means that the eyepiece has an extended field of view (WF — wide, EWF — extra wide, UWF — extra wide).

— Eyepiece tilt. The tilt of the eyepiece determines the position of the observer's head when looking through the microscope and the overall usability. According to this indicator, three main options can be distinguished: fixed angle, adjustable angle, without tilt. The fixed angle is most often 30° or 45° relative to the horizontal, these values are considered the most convenient. In angle-adjustable microscopes, the entire stand, with tube and stage, is fixed to the base with a swivel mount. This is the most convenient option, allowing you to adjust the tilt to your preference, but the mount tends to become loose over time, so it is rarely used in professional microscopes. The third variety — vertical microscopes, without tilt — have not received much distribution: this design is used in some stereoscopic models (see "Type") in order to ensure that the stage remains strictly horizontal (this is important for some work with microscopic objects).

— Rim diameter. The nominal diameter of the eyepiece used in the microscope, as well as the diameter of the hole in the tube, designed to install the eyepiece. Several standard diameters are used in modern microscopes, in particular 23 and 27 mm. In fact, this parameter is necessary, first of all, if you plan to purchase spare or replacement eyepieces for the microscope, or if you already have an eyepiece on the farm, and you need to evaluate its compatibility with this model.

— Diopter adjustment. The range of diopter correction provided in the eyepiece. This correction is used so that a nearsighted or farsighted person can look through the microscope without glasses or contact lenses. In most models with this function, the correction range is about 5 diopters in both directions; this allows the microscope to be used for low to moderate myopia/farsightedness.

This feature means that the eyepiece that the microscope is equipped with can rotate around a vertical axis — in other words, right and left. Typically, the range of rotation is a full 360°.

The swivel head of the eyepiece does not affect the main features and capabilities, but provides additional convenience for the user: the eyepiece can be rotated to the optimal position depending on the situation. This can be useful, for example, when two students or laboratory assistants sitting next to each other use one microscope with a preparation for two — if necessary, each can turn the eyepiece towards him without moving the entire device. The reverse side of this advantage is some complication of the design and an increase in its price.

The presence of light filters in the scope of delivery of the microscope.

Light filters are installed in the lighting system; they can be interchangeable or built-in (usually on a turret). Anyway, such devices change the characteristics of light, adjusting it to the specifics of the situation. The types and purpose of light filters can be different, as well as their range in the kit; here are some of the most common options:

— Blue colour. Useful in cases where light from an incandescent or "halogen" lamp is used for illumination. Such a filter equalizes the colour temperature (white balance), making the shades of colours colder and providing natural colour reproduction; this is especially important for microphotography, since a properly set white balance is critical to obtaining high-quality images.

— Yellow colour. Kind of the opposite of blue: lowers the colour temperature, giving the image a warmer tint. It is also sometimes useful for adjusting white balance, but yellow filters have another important use: they are well suited for detecting imperfections in metallic surfaces.

— Green colour. Achromatic and planachromatic objectives, which are installed in most modern microscopes, are best at eliminating aberrations in the green part of the spectrum. With this in mind, similar filters are applied: an image painted in a green tint has the least visible distortion. In addition, most objectiv...es for phase contrast microscopy are also most effective in the green part of the spectrum (although exceptions are possible).

— Matte (diffuser). White colour filters that do not change the colour of the light, but provide additional dispersion. This can be useful, in particular, when working with low magnification lenses.

— Neutral. Filters in different shades of grey. Used to reduce the intensity of lighting without changing its other characteristics. Such devices can be especially useful when taking photographs — namely, if the camera does not have a sufficiently fast shutter speed. Note that a similar effect can be achieved using a microscope diaphragm, but this is not always the best option when shooting. So, narrowing the aperture reduces the field of view and increases the depth of field (the latter is also not always desirable), while filters do not affect these parameters; besides, in some situations, even the narrowest aperture may not be “dark” enough.

— Light filters for coloured preparations. Improve the visibility of elements painted in a particular colour. Such fixtures are especially popular in biological studies, as they are the most commonly stained specimens and are also the most susceptible to dye fading, making it difficult to view under normal lighting conditions. Note that filters of this type, in contrast to the colour filters described above, do not colour the entire image in a certain colour, but only muffle all other colours, except for their “native”.

— Fluorescent. Filters used in fluorescence microscopy. They are divided into two types — exciting (they separate UV radiation from the general backlight spectrum to illuminate the drug) and closing (protect the user's eyes from ultraviolet radiation and at the same time let the fluorescent glow of the drug pass through).