What are the classifications of microscope objectives?
⑴According to the length of the microscope lens barrel (in mm): 160 lens tube for transmitted light, with a 0.17mm thick or thicker cover glass; 190 lens tube for reflected light, without
With cover glass; lens tube for transmitted light and reflected light, tube length is infinite.
⑵Features of immersion method: non-immersion type (dry type), immersion type (oil immersion, water immersion, glycerin immersion and other immersion methods).
⑶According to the optical device: transmissive, reflective and catadioptric.
(4) According to numerical aperture and magnification: low magnification (NA≤0.2 and β≤10X), medium magnification (NA≤0.65 and β≤40X), high magnification (NA>0.65 and
β>40X).
⑸According to the situation of correcting aberrations, it is usually divided into achromatic objective lens, semi-apochromatic objective lens, apochromatic objective lens, flat-field achromatic objective lens, flat-field achromatic objective lens,
Field Apochromatic Objectives and Monochromatic Objectives.
⒈Achromatic objective lens (Achromatic) is a relatively common objective lens (Table 1-1).
Composed of mirrors, it can only correct the axial chromatic aberration of red light and blue light in the spectral line. Simultaneously corrected on-axis point spherical aberration and paraxial point coma aberration, this objective cannot
Eliminate the secondary spectrum, only correct the spherical aberration and chromatic aberration in the yellow and green wave regions, but not eliminate the remaining chromatic aberration and spherical aberration and chromatic aberration in other wave regions, and the image field curvature
The curvature is still very large, that is to say, only a clear image in the middle range of the field of view can be obtained. When using it, it is advisable to use yellow-green light as the lighting source, or insert it in the optical path
Yellow-green filter. This type of objective lens is simple in structure, economical and practical, and is often used in conjunction with Forgen eyepieces and correction eyepieces, and is widely used in medium and
on a low power microscope. When taking black and white photos, green color filters can be used to reduce residual axial chromatic aberration and obtain photos with good contrast.
2. Apochromatic objective lens (Apochromatic) is composed of multiple groups of special optical glass and advanced lens groups made of fluorite. red, blue,
Yellow light corrects the axial chromatic aberration and eliminates the secondary spectrum, so the image quality is very good, but there are many lenses, and it is difficult to process and install. Correction of chromatic aberration in
All wave regions of visible light. It is better to add blue or yellow filter. It is the most excellent objective lens in the microscope, and it is resistant to spherical aberration and chromatic aberration.
Has better calibration and is suitable for high magnification. However, it still needs to be used in conjunction with compensating eyepieces to eliminate residual chromatic aberration.
⒊Plana chromatic objective lens (Plana chromatic) adopts a complex optical structure composed of multiple lenses, which can better correct astigmatism and curvature of field,
The entire field of view can be displayed clearly and is suitable for photomicrography. The correction of spherical aberration and chromatic aberration of this objective lens is still limited to the yellow-green wave region, and there are still remaining
chromatic aberration.
⒋Planapochromat objective lens (PF, Planapochromat) In addition to further correction of field curvature, other aberrations are corrected to the same degree as apochromat
The difference objective lens is the same, so that the image is clear and flat; but the structure is complex and difficult to manufacture.
5. Half apochromatic objective lens (Halfapochromatic) Some lenses are made of fluorite, so it is also called fluorite objective lens, and its performance is better than that of achromatic objective lens.
Cheaper than apochromatic objectives. The degree of correction of aberrations is between the achromatic and apochromatic objectives, but other optical properties are the same as the latter
Similar; less expensive and best used with compensating eyepieces.
6. Special objective lens The so-called special objective lens is specially designed to achieve certain effects on the basis of the above objective lens. According to the purpose, there are mainly the following
Several:
1) phase contrast objective This objective lens is a special lens for phase contrast microscopy (of course, it can also be used routinely).
The characteristic is that a phase plate is installed at the rear focal plane of the objective lens, which has achieved the purpose of delaying light waves.
2) The correction collar objective is equipped with a ring-shaped adjustment ring in the objective lens. When turning the adjusting ring, the adjustable
The distance between the lens groups (usually the second and third groups of lenses) in the objective lens, so as to correct the overlay caused by the non-standard thickness of the cover glass
Difference.
3) The iris diaphragm objective is equipped with an iris diaphragm in the upper part of the objective lens barrel, and there is also a rotatable diaphragm on the outside
The adjustment ring can adjust the size of the aperture when turning. This structure is the most advanced oil immersion objective lens.
4) Strain-free objective This kind of objective lens overcomes the existence of stress in the assembly of the lens group, and is designed for transmission
The objective lens used for polarizing microscope inspection can achieve better polarizing microscope inspection effect.
5) The non-fluorescing objective is an objective lens dedicated to epifluorescent microscopes. Even if this objective lens is subjected to
It does not emit fluorescence when a strong excitation light source is used.
6) no cover objective Some inspected objects, especially smeared slides, etc., cannot be covered with a cover glass, so
A coverless objective lens should be used during microscopic examination, otherwise the image quality will be significantly reduced, especially during high-magnification microscopic examination.
