Re-understanding of effective magnification of microscope
The relationship between the effective magnification (M) of the microscope and the numerical aperture (NA) of the objective lens can be expressed as: 550NA; for a long time, microscope users have followed this relationship. However, VanderVoort in his book " The book Metallography—Principles and Practice points out that the above formula is derived under the condition of observing objects with ideal contrast with ideal eyes, so don’t follow it as a dogma. In fact, the resolution is not only related to the resolution of the objective lens Related, but also related to the contrast of the object image. In addition, lighting conditions, magnification, objective lens quality, and observation conditions will all affect the contrast of the object image, and thus also affect the resolution. He pointed out that in order to obtain the highest resolution, the minimum effective magnification It should be about 4 times under the best conditions, that is, M≈2200NA; at the same time, it is completely reasonable to use photomicrographs with magnifications of 4000× or higher.
