Reasonable combination of the objective and eyepiece of an optical microscope
When selecting objective lenses and eyepieces, two main considerations are:
Matching on the first category. All flat field objective lenses must be used in conjunction with specially designed flat field eyepieces.
Secondly, a reasonable matching of amplification factors. At a certain magnification, the objective and eyepiece can be combined arbitrarily, but the premise of their combination is mainly to consider the effective magnification, which is an important rule for the correct use of microscopes. The effective magnification of a microscope is 500-1000 times the numerical aperture of the objective lens used, that is, the product of the magnification of the objective lens and the eyepiece is equal to 500-1000 times the numerical aperture of the objective lens.
If you use a 40X objective with a numerical aperture of 0.65 to observe the specimen, what size should you choose
Firstly, calculate the total effective magnification based on the effective magnification, and then divide by 40 to determine the appropriate magnification for the eyepiece. The calculation process is: (0.65 × 500~0.65 × 1000) ÷ 40 ≈ 8-16. That is to say, for an objective lens with a numerical aperture of 0.65, an 8-16 times eyepiece should be selected to match it within the effective magnification range (500-1000 times). If the eyepiece magnification is too low and the total magnification is too small, the resolution of the objective lens cannot be fully utilized. Details that could have been recognized are difficult to distinguish due to the small total magnification when squeezed together. The magnification obtained by an eyepiece that is higher than 16 times is called "empty magnification", which does not improve the resolution of details and instead has a small clear depth, which cannot clearly reflect the structure at different levels.
