Flat field apochromatic objective and monochromatic objective.
Achromatic objective is a common type of objective (Table 1-1), which is composed of several groups of surfaces with different radii, one positive and one negative, glued together for transparency
Mirror composition can only correct the axial color difference between red and blue light in the spectral lines. At the same time, the on axis spherical aberration and near axis point coma were corrected, and this type of objective cannot
Eliminating the secondary spectrum, only correcting for spherical and chromatic aberration in the yellow and green wave regions, without eliminating the remaining chromatic aberration and spherical and chromatic aberration in other wave regions, and the image field curvature is still significant, which means that only a clear image in the middle range of the field of view can be obtained. When using, it is advisable to use yellow green light as the lighting source, or insert a yellow green filter in the optical path. This type of objective has a simple structure, is economical and practical, and is often used in conjunction with Fukugen eyepieces and correction eyepieces. It is widely used in medium and low magnification microscopes. In black and white photography, a green filter can be used to reduce residual axial color difference and obtain photos with good contrast.
Apochromatic objective is a combination of advanced lenses made of multiple special optical glasses and fluorspar. The axial color difference has been corrected for red, blue, and yellow light, eliminating the secondary spectrum, resulting in good image quality. However, there are many lenses, making processing and installation difficult. The correction of color difference is in the entire wavelength range of visible light. If blue or yellow filters are added, the effect will be better. It is the best objective in microscopes, with good correction for spherical and chromatic aberration, suitable for high magnification. But it still needs to be used in conjunction with compensating eyepieces to eliminate residual color difference.
The Plana chromatic objective adopts a complex optical structure composed of multiple lenses, which can effectively correct astigmatism and image field curvature, making the entire field of view clear and suitable for micrography. The correction of spherical and chromatic aberration by this objective is still limited to the yellow green wave region, and there is still residual chromatic aberration.
4. Planapochromatic objective (PF), except for further image field bending correction, all other aberration correction levels are the same as those of the apochromatic objective, making the image clear and flat; But the structure is complex and manufacturing is difficult.
Half apochromatic objective lenses are made of fluorite, hence also known as fluorite objective lenses. They have better performance than apochromatic objective lenses and are cheaper in price than apochromatic objective lenses. The degree of aberration correction falls between the two types of objective lenses: achromatic and apochromatic, but other optical properties are similar to the latter; Low price, best used in conjunction with compensating eyepieces.
