To calculate the somatic cell count in a sample, I need to find out the field of view of 100X objective lens. How can I determine the diameter/area of the microscopic field?
Hello Tanvi Bhatia
To determine the field of view (FOV) of your microscope, first examine the microscope itself. The microscope’s eyepiece should be labeled with a sequence of numbers, such as 10x/22 or 30x/18. These numbers are the eyepiece magnification and the field number, respectively. Also, take note of the magnification of your objective lens at the bottom of the microscope, if applicable – generally 4, 10, 40 or 100 times.
Once you’ve taken note of the eyepiece magnification, field number and objective lens magnification number, if applicable, you can calculate your microscope’s field of view by dividing the field number by the magnification number. For example, if the microscope’s eyepiece reads 30x/18, then 18 ÷ 30 = 0.6, or an FOV diameter of 0.6 millimeters. If your microscope only uses an eyepiece, this is all you need to do, but if your microscope uses both an eyepiece and an objective lens, multiply the eyepiece magnification by the objective magnification to find the total magnification before dividing the field number.
For example, if the eyepiece reads 10x/18, and the magnification of your objective lens is 40, multiply 10 and 40 to get 400. Then divide 18 by 400 to get an FOV diameter of 0.045 millimeters.
Whenever you change microscopes or switch eyepieces or objective lenses, remember to repeat the FOV calculations with the new field number and magnifications. When dealing with objects observed at higher magnifications, it may be useful to convert your measurements from millimeters to micrometers. To do so, multiply the FOV diameter in millimeters by 1,000 to convert the diameter to micrometers.
Also, refer to the link below.
https://sciencing.com/do-cell-size-under-microscope-6962408.html
Good Luck.
Dear Tanvi Bhatia
However, with a more modern microscope, it is necessary to take into account the factors of other optical elements, such as the trinocular head. It is certainly better to measure FOV directly. Analysis of the image captured by the camera also requires magnification calibration. There are microscopic calibration plates for this purpose, which are monitored as normal samples and allow the FOV to be measured directly in micrometers. It's not even extremely expensive (about $ 20). In case of emergency, it is also possible to use a micrometer scale, removed from the measuring objective.
Use of a calibration plate is the best choice. You may also take photos from that for various combinations of magnifying lenses (up to 3 in some microscopes) and keep them for comparing with photos of your objects.
If you what sensor your microscope is using then you can determine the FOV by the following equation. Full FOV = (Sensor_Size*Obj_Dist)/EFL. Sensor_Size is the physical size of the CCD/CMOS chip in mm units. The Obj_Dist is the range or distance of the object to the objective and EFL is the effective focal length in mm units, or use whatever units you want.
The best way to measure this is to place a microscope slide under the scope and measure the distance from the objective to the slide, and then mark on the slide the edges of the field as you are looking through the scope (or observing on the CCD screen) then measure the distance between the marks. This is the FOV, which you can then convert to radians, degrees or arcsec/arcmin by dividing the FOV by the range (Obj_Dist). Convert radians to degrees by multiplying it by (180/pi). Convert from degrees to arcsec by multiplying it by 3600.
I agree with Dalibor Matýsek. If you don't have a microscope calibration plate to hand, and you want a fast approximation, you may wish to consider viewing a Compact Disc. Old technology, but the track pitch is 1.6microns +/-6% (0.74microns for DVD) so you can count the number of tracks that fill the field of view (assuming that your field of view is
I agree with George Hood about calibrating a microscope using the CD. Very amazing!
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