Hi Vladimir,

the size of the field of view is given by the combination of all optical elements (eg objective, tubelens, ocular and may be an additional magnification) of the microscope in between the object and your eye or the camera you are using.

What changes the field of view when you change the objective is the objectives magnification. for example changing from a 10x to a 100x objective will shrink your fiel of view by a factor of 10.

The NA will in contrast only affect the resolution you can gain, this is described by Abbe's equation d = wavelength of light / 2 NA.

you can measure your field of view using a microscopic ruler for one objective and calculate the field of view via the magnification factor for the other objectives you are using.

Best regards

I would strongly endorse Thorge's reply Vladimir. 

Place something you know the size of (ruler) in the system and image it.  as the Americans would say -suck it and see.  There is nothing like a good cold hard measurement to overturn the results from a beautiful theoretical analysis.

good luck

Dear Vladimir,

The real extent of the visual field of a microscope is best calculated using a real micrometer scale. For any lens, the lengths and widths can be made visible. In the attached images below some examples are documented with a camera. There are micrometer scales for transmitted and reflected light microscopy. The micrometer scale

used below measures 1mm in lenght. The same applies to the circular field of view of an eyepiece.

Best regards,

Guenter

where to buy such a scale?

You can buy such a scale from several company's, for example 

http://www.thorlabs.de/newgrouppage9.cfm?objectgroup_id=4338

http://www.edmundoptics.com/testing-targets/test-targets/image-analysis-test-targets/dual-axis-linear-scale-stage-micrometer/2701

or just search the web for microscope scale...

Though I recommend the previous suggestions first--measuring a known object and using that as your reference point--another option is just doing some time on Google, or whatever, to get the specs of your equipment. This also may be a good check for knowing your uncertainty/error margin.

As in an optics lab I was recently apart of, I needed to find out a particular wavelength of an unknown light. The Direct Measurement Microscope in the lab (DMM) had markings on it, but no units. But quick research shed some light (pun) on which units were to be used, which then I could back-track with lens distances and focal points (thin lens equation) to tell the correct and actual size of the dispersion pattern. This gave me a theoretical answer to work with as well as the experimental.

Hi Vladimir, One option is use a physical scale and calibrate them. Calculate the physical area for different magnifications of the system. The projection of this can be used to calculate the physical area for other magnification values which was not measured. 

Hello Vladimir,

I would suggest to look for optical metrology reticles, scale reticles, zoom reticles, etc. They are commercially available and there is a very wide range of those reticles. You can select the one that suits the best your microscope based on your magnification and your optical detection system. Once when you find the reticle that is the best for your system you can figure out what is your actual field of view.

Hope this helps.

the field of view is calculated by the field number of the eyepiece  divided by the objective magnification .Modern objectives can have a field number of 28 (wide field objectives) as oppsed to 18 (older) and 22. An example of a super wide field objective would be a x20 objective with an NA of  1.0  thus achieving  the resolution of a standard x80 objective with as very low field of view (costs 20k+ though) . Many manufacturers have brought out wide field of view oil imersion objectives   eg x60  NA 1.4

back to this topic.......How can you calculate the volume of blood stain under the Field of View?