For both setups, the angular measurement from the lens axis to the frame edge is called ‘Angle’, measured in degrees. The FOV of the lens is twice the value of ‘Angle’.

Field of view vs focal lengthreddit

Microscopes are powerful tools that allow us to explore the intricate details of the unseen world. A key component in this exploration is the mechanical stage, a platform that holds the specimen and enables precise movement for detailed observation.

The mechanical stage is designed to move the specimen smoothly and accurately. It typically employs a rack-and-pinion mechanism or a ball-bearing system.

Field of view vs focal lengthcamera

Using these techniques, you could actually find out what an un-marked lens’ focal length is. You could also verify (or debunk) manufacturer claims about the real focal length of a lens.

Field of viewcamera

As its name suggests, the mechanical stage is a platform with a mechanical system for precise movement. This system typically involves knobs or levers that control the stage's movement in two directions: X (left-right) and Y (forward-backward). This allows you to easily position the specimen under the objective lens without having to manually move the slide.

One reason you might like to measure this stuff, versus just reading the lens focal length stamped on the lens, is that manufacturers often lie about the true lens focal length. This is particularly true of long zooms, which might not be as long as claimed. It’s often the case that a lens focal length reduces drastically when focusing close (called focus breathing), and these techniques could attach real numbers to that.

Field of viewcalculator

What isfocal length oflens

I made all of the distance measurements relative to the lens axis and to a spot on the lens that I guessed to be near the vertex of the red arrows shown in the diagram. You don’t really need to know this location, since these techniques will actually calculate the location.

The diagrams above show the setup to align and measure your lens to get the information for calculating the focal length and field of view (FOV).

The mathematics used in the calculations involves both algebra and trigonometry. Any “scientific” calculator has the necessary features to do this math. You can always download a scientific calculator app onto your smartphone. Fear not the math.

My setup was on a tile floor, and I used the tile grout lines to make sure the lens axis was exactly perpendicular to the wall. You could also temporarily tape a little mirror against the wall and line up the camera until you see your reflection in the center of the camera’s field of view.

FOV tofocal lengthcalculator

The nearer wall distance setup is called ‘x’. The farther wall distance setup is called ‘X’. Similarly, the distance along the wall from the frame middle to the frame edge in the nearer wall setup is called ‘y’, while the farther distance setup is called ‘Y’.

Note: The above links are fictitious and used for demonstration purposes only. Please consult reliable sources for accurate information about microscopy.

Field of viewhuman eye

As shown above, I put some tape targets on the wall that point at the edges of the field of view and the exact center of the frame. I made sure that the distances on either side of the middle of the frame exactly matched. I also made sure that the lens was at exactly the same height as the middle wall target. Using high magnification via Live View or the viewfinder helps getting the targets more precise.

To get all of the necessary information, you’ll need to set up some targets on a wall (I used painter’s tape) and then take distance measurements at two different camera-to-wall distances.

Imagine trying to examine a tiny sample under a microscope without the aid of a mechanical stage. You'd have to manually move the slide, risking the possibility of damaging the specimen or losing your target area. The mechanical stage solves these issues by providing:

I happen to have a fun little laser that can make extremely accurate measurements over long distances. I used this device to get my targets placed within a millimeter, and to measure the camera-to-subject distance.

Field of view vs focal lengthcanon

In conclusion, the mechanical stage is an indispensable part of a microscope, playing a crucial role in enabling precise and controlled specimen manipulation. By providing ease of use, stability, and precision, the mechanical stage allows us to explore the microscopic world with clarity and accuracy.

As I often say, “garbage in, garbage out”. The more accurate measurements you make, the more accurate your results will be.

You only need to take 6 different measurements to calculate everything! The trick is in setting up the targets to make those measurements accurate.