PeteM wrote: ↑Fri Mar 29, 2024 1:06 am
This may be QWERTY vs. Dvorak keyboards.
Having gotten used to field numbers, FN certainly eems simple enough. Use a 10x/22 eyepiece and I expect to see a 22mm wide field with a 1x stereo objective and a 2.2mm field with a 10x compound objective. Put a ruler or micrometer slide down and take a look. It's simple math and easy to measure. I do it frequently with stereo microscopes and sometimes with compound microscopes. And when (as has happened) a Chinese stereo eyepiece promises a 23mm field and only delivers 20mm at 1x (on a scope where other markings are true), I near instantly know not to trust that vendor
There are two side benefits of this calculation.
1. If the field of view does not calculate from the known properties, either the FN number is not correct, or the objective magnification is not as indicated. It is possible to actually calculate the objective magnification by knowing the FN and observing the measurable field of view. A 20mm FOV with a 20mm FN results in a 1x objective lens. A 2.0mm FOV with a 20mm FN results in a 10x objective..
As PeteM points out if the numbers don’t compute, there is good reason to question the information from the supplier..
One consideration to take into account is on a zoom based stereo, the indication of the zoom position could have some parallax error or just be off in the knob setting.
2. When you need to know the correct magnification in order to view the entire object size in one view, by knowing the field of view of a particular objective/eyepiece combination will allow you to select the right objective. The is true for both compound and stereo scopes. A pathologist will want to be able to see the entire tumor area on a tissue section. A PC board assembly worker needs to see the entire work area in a single view.
By knowing how big the sample area is, allows the simple selection of the correct objective magnification.