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[Recommend] the optical principle of microscope and function
From;    Author:Stand originally
TraditionalOptical microscopeBasically reach the rigid structure composition that props up them by optical system, optical system includes field lens, ocular and condenser, it is by the complicationed magnifier of all sorts of optical glass make it. Field lens magnifies the specimen picture, its magnify fold M content decides by next type: F of ∕ of Δ of M content = ' content, the F in type ' the focal length that content is field lens, Δ can understand for the distance between field lens and ocular. Ocular resembles what field lens place becomes magnifying again, be in into a virtual image person at the moment 250mm place observes for the person, this is the observation position that most person feels the most comfortable, the =250/f of fold M eye of ocular ' eye, f ' the focal length that eye is ocular. The total enlarge fold of microscope is the product of field lens and ocular, namely F of ∕ of *250 of Δ of = of eye of M=M content *M ' eye *f; content. Visible, reduce field lens and ocular focal length to will make always magnify fold rises, this is to use microscope to be able to see the microbial key such as the bacterium, also be the discriminative place of its and common magnifier.

So, whether can imagine absoluteness ground to reduce F ' content F ' eye, so that raise enlarge fold, make we can see more subtle object? The answer is negative! Because in order to becomes the smooth essence that resemble,this is it is a kind of electromagnetic wave, be unavoidable to produce diffraction and interference phenomenon in transmitting a process consequently, when the ripple that sees surface like daily place encounters an obstacle can circuitous, like can be strengthened each other when two Shui Bo encountering or be being weakened. When the light-wave that gives out from dot of content of glow of a punctate enters field lens, the frame block up of field lens smooth transmission, generate diffraction and interference, can no more meet after classics field lens collect at a bit, form the facula that has certain volume however, periphery still has strength faint and a series of aureola of wear off, we call central bright spot Ai Li spot, the two facula when two glow dot stands by certain distance can overlap, till cannot affirm,be two facula. Rayleigh put forward to decide standard, when thinking when two facula center apart is equal to radius of Ai Li spot, two facula can differentiate, classics computation, at that time two glow nod the distance E=0.61 between to enter ∕ N.A into ∕ N.sinA=0.61, in type, enter for light-wave wavelengh, person eye is acceptable light-wave wavelengh is about 0.4, 0.7um, n is nodded to give off light located the refractive index of medium, if lie in air, n ≈ 1, lie in water, n ≈ 1.33, and A nods Zhang Jiao of pair of field lens frame to give off light, n.A calls the numeric aperture of field lens. From go up form is visible, the between 2 o'clock distance that field lens can differentiate got the limitation of smooth wavelengh and numeric aperture, as a result of person eye vision most the wavelengh of acumen is 0.5um about, and A horn exceeds 90 degrees impossibly, sinA always is less than 1, pervious to light to practicable the oldest refractive index is medium about 1.5, reason E value is more than 0.2um from beginning to end, this is the distance of the smallest limit that optical microscope can differentiate. Through microscope enlarge is become picture, if think aux will be able to is had,the E of content dot span of the field lens resolution that certain N.A is worth magnifies enough is differentiated by person eye, need M.e ≥ 0.15mm, the park that the person eye that here 0.15mm reachs for the experiment can differentiate at the moment 250mm is in the least space between two small matter, reason M ≥ (0.15 ∕ 0.61 enter) N.A ≈ 500N.A, do not send to make observe too arduous, m expands one times enough, namely 1000N.A of ≤ of 500N.A ≤ M, be microscope total fold is reasonable choose limits, again big total enlarge fold is no point, because of field lens numerical value bore diameter had been restricted the smallest distinguishable distance, raise enlarge fold impossible already resolution gives less object detail.
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