What is the capacity to distinguish two adjacent points in microscope
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The most commonly used microscope for general purposes is the standard compound microscope. It magnifies the size of the object by a complex system of lens arrangement.
It has a series of two lenses; (i) the objective lens close to the object to be observed and (ii) the ocular lens or eyepiece, through which the image is viewed by eye. Light from a light source (mirror or electric lamp) passes through a thin transparent object (Figure 4.4).
The objective lens produces a magnified ‘real image’ first image) of the object. This image is again magnified by the ocular lens (eyepiece) to obtain a magnified ‘virtual image’ (final image), which can be seen by eye through the eyepiece. As light passes directly from the source to the eye through the two lenses, the field of vision is brightly illuminated. That is why; it is a bright-field microscope.
Parts of a Compound Microscope:
The parts of a compound microscope are of two categories as given below:
(i) Mechanical Parts:
These are the parts, which support the optical parts and help in their adjustment for focusing the object (Figures 4.5 and 4.6).
The components of mechanical parts are as follows:
1. Base or Metal Stand:
The whole microscope rests on this base. Mirror, if present, is fitted to it.
2. Pillars:
It is a pair of elevations on the base, by which the body of the microscope is held to the base
3. Inclination joint:
It is a movable joint, through which the body of the microscope is held to the base by the pillars. The body can be bent at this joint into any inclined position, as desired by the observer, for easier observation. In new models, the body is permanently fixed to the base in an inclined position, thus needing no pillar or joint.
4. Curved Arm:
It is a curved structure held by the pillars. It holds the stage, body tube, fine adjustment and coarse adjustment.
5. Body Tube:
It is usually a vertical tube holding the eyepiece at the top and the revolving nosepiece with the objectives at the bottom. The length of the draw tube is called ‘mechanical tube length’ and is usually 140-180 mm (mostly 160 mm).
6. Draw Tube:
It is the upper part of the body tube, slightly narrower, into which the eyepiece is slipped during observation.
7. Coarse Adjustment:
It is a knob with rack and pinion mechanism to move the body tube up and down for focusing the object in the visible field. As rotation of the knob through a small angle moves the body tube through a long distance relative to the object, it can perform coarse adjustment. In modern microscopes, it moves the stage up and down and the body tube is fixed to the arm.
8. Fine Adjustment:
It is a relatively smaller knob. Its rotation through a large angle can move the body tube only through a small vertical distance. It is used for fine adjustment to get the final clear image. In modern microscopes, fine adjustment is done by moving the stage up and down by the fine adjustment.
9. Stage:
It is a horizontal platform projecting from the curved arm. It has a hole at the center, upon which the object to be viewed is placed on a slide. Light from the light source below the stage passes through the object into the objective.
10. Mechanical Stage (Slide Mover):
Mechanical stage consists of two knobs with rack and pinion mechanism. The slide containing the object is clipped to it and moved on the stage in two dimensions by rotating the knobs, so as to focus the required portion of the object.
11. Revolving Nosepiece:
It is a rotatable disc at the bottom of the body tube with three or four objectives screwed to it. The objectives have different magnifying powers. Based on the required magnification, the nosepiece is rotated, so that only the objective specified for the required magnification remains in line with the light path.
(ii) Optical Parts:
These parts are involved in passing the light through the object and magnifying its size.
The components of optical parts include the following:
1. Light Source:
Modern microscopes have in-built electric light source in the base. The source is connected to the mains through a regulator, which controls the brightness of the field. But in old models, a mirror is used as the light source. It is fixed to the base by a binnacle, through which it can be rotated, so as to converge light on the object. The mirror is plane on one side and concave on the other.
It should be used in the following manner:
(a) Condenser Present:
Only plane side of the mirror should be used, as the condenser converges the light rays.
(b) Condenser Absent:
(i) Daylight:
Plane or concave (plane is easier)
(ii) Small artificial light:
High power objective: Plane side
Low power objective: Concave side
2. Diaphragm
It has a series of two lenses; (i) the objective lens close to the object to be observed and (ii) the ocular lens or eyepiece, through which the image is viewed by eye. Light from a light source (mirror or electric lamp) passes through a thin transparent object (Figure 4.4).
The objective lens produces a magnified ‘real image’ first image) of the object. This image is again magnified by the ocular lens (eyepiece) to obtain a magnified ‘virtual image’ (final image), which can be seen by eye through the eyepiece. As light passes directly from the source to the eye through the two lenses, the field of vision is brightly illuminated. That is why; it is a bright-field microscope.
Parts of a Compound Microscope:
The parts of a compound microscope are of two categories as given below:
(i) Mechanical Parts:
These are the parts, which support the optical parts and help in their adjustment for focusing the object (Figures 4.5 and 4.6).
The components of mechanical parts are as follows:
1. Base or Metal Stand:
The whole microscope rests on this base. Mirror, if present, is fitted to it.
2. Pillars:
It is a pair of elevations on the base, by which the body of the microscope is held to the base
3. Inclination joint:
It is a movable joint, through which the body of the microscope is held to the base by the pillars. The body can be bent at this joint into any inclined position, as desired by the observer, for easier observation. In new models, the body is permanently fixed to the base in an inclined position, thus needing no pillar or joint.
4. Curved Arm:
It is a curved structure held by the pillars. It holds the stage, body tube, fine adjustment and coarse adjustment.
5. Body Tube:
It is usually a vertical tube holding the eyepiece at the top and the revolving nosepiece with the objectives at the bottom. The length of the draw tube is called ‘mechanical tube length’ and is usually 140-180 mm (mostly 160 mm).
6. Draw Tube:
It is the upper part of the body tube, slightly narrower, into which the eyepiece is slipped during observation.
7. Coarse Adjustment:
It is a knob with rack and pinion mechanism to move the body tube up and down for focusing the object in the visible field. As rotation of the knob through a small angle moves the body tube through a long distance relative to the object, it can perform coarse adjustment. In modern microscopes, it moves the stage up and down and the body tube is fixed to the arm.
8. Fine Adjustment:
It is a relatively smaller knob. Its rotation through a large angle can move the body tube only through a small vertical distance. It is used for fine adjustment to get the final clear image. In modern microscopes, fine adjustment is done by moving the stage up and down by the fine adjustment.
9. Stage:
It is a horizontal platform projecting from the curved arm. It has a hole at the center, upon which the object to be viewed is placed on a slide. Light from the light source below the stage passes through the object into the objective.
10. Mechanical Stage (Slide Mover):
Mechanical stage consists of two knobs with rack and pinion mechanism. The slide containing the object is clipped to it and moved on the stage in two dimensions by rotating the knobs, so as to focus the required portion of the object.
11. Revolving Nosepiece:
It is a rotatable disc at the bottom of the body tube with three or four objectives screwed to it. The objectives have different magnifying powers. Based on the required magnification, the nosepiece is rotated, so that only the objective specified for the required magnification remains in line with the light path.
(ii) Optical Parts:
These parts are involved in passing the light through the object and magnifying its size.
The components of optical parts include the following:
1. Light Source:
Modern microscopes have in-built electric light source in the base. The source is connected to the mains through a regulator, which controls the brightness of the field. But in old models, a mirror is used as the light source. It is fixed to the base by a binnacle, through which it can be rotated, so as to converge light on the object. The mirror is plane on one side and concave on the other.
It should be used in the following manner:
(a) Condenser Present:
Only plane side of the mirror should be used, as the condenser converges the light rays.
(b) Condenser Absent:
(i) Daylight:
Plane or concave (plane is easier)
(ii) Small artificial light:
High power objective: Plane side
Low power objective: Concave side
2. Diaphragm
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