The sales range of our microscope covers stereo microscope, metallurgical microscope and measuring microscope.
Take Metallurgical IMS-300 as an example, the standard delivery for eyepiece is 10 times Throughout all of the microscope (including bio-microscope), all of 10 times eyepiece for standard delivery. We all know that the overall magnification microscope objective lens is equal to the objective times multiple eyepiece times, such as metallurgical microscope IMS310, it use 40 times objective lens ,10 times the eyepiece, its total magnification is 400 times. Why not use greater rate eyepiece? For example 20 times, 30 times ... ... greater rate, larger magnification, isn’t it?
Today, on this question we first learn some knowledge of microscope.
First of all, we need to know the term - NA (also known as mirror port rate, abbreviated as NA). It is a medium between the object and the product of lens refractive rate η with sine value of the half of the objective lens aperture angle (a / 2) ,its size is determined by:
N.A = η · sin a / 2
Microscope resolution D: microscope distinguished the minimum distance between two points that the microscope can distinguish, namely, the resolution of microscopes.
D =
The formula: A is the wavelength of light:
η is the refractive index of the object, when the object in the air η = 1;
a is the aperture angle.
When the objective lens numerical aperture NA is not big enough, that is, the resolution rate is not high enough, the microscope can not distinguish the fine structure of the object, then even if the excessive increase magnification, what we received is only an great outline, but details is unclear image. This kind of excessive magnification is invalid. Conversely, if the resolution has been satisfied while the magnify rate is insufficient, the microscope still owns the potential resolution ability. But the image is too small and still can’t be clear for the human eyes.
To maximize the resolving power of microscope, numerical aperture NA should match with the total magnification microscope reasonably ,so as to meet with the following conditions:
500N.A <Microscope Total Magnification <1000N.A - (2)
The magnification within this range was an effective magnification. Since sin a / 2 is always less than 1, the highest material side space refractive index η of about 1.5, NA cannot be greater than 1.5, the resolution of optical microscopy is restricted by formula(1), with certain limits.
Microscope user should determine the required numerical aperture NA by formula (1) based on the required resolution minimum size, and then select the total magnifier and objective magnifier by formula(2).
When we use Sinowon Inverted Metallurgical Microscope (IMS300) with NA 0.65 and 40X objective, firstly, calculate the total times according to the effective magnification, then divided by 40, that is, the times of eyepiece should be selected.
The Calculation is: 0.65 × 500 ≈ 8 ~ 0.65 × 1000 ÷ 40 ≈ 16.
That is: the objective lens numerical aperture of 0.65, the effective rate of 500 to 1000 times magnification range should select 8 to 16 times the eyepiece to match. If the eyepiece ratio is too low, the total magnification is too small, the resolution can’t fully play a role, the identifiable details became difficult to distinguish, because the total magnification is too small.
Finally, we should note the matches between different types, that is, the flat-field objective should use with a special flat field eyepiece.
