For our project, we need to know the magnifying power of a lens with a fairly high degree of accuracy. Some lenses have unknown or obviously inaccurate magnification information, while others have approximately accurate information that is not precise enough for computations. In either case, it is useful to be able to calculate the magnifying power for ourselves.
A microscope slide like the one above, whose divisions are a known distance apart, is used to perform the calculation.
First, a picture is taken of the ruler slide using the desired magnification. Next, the individual pixels between two divisions are counted. This is done using any editing software with a single-pixel brush size. Finally, the pixel size on the sensor plane of the imaging device must be known. Camera documentation should include this information.
Magnification is found by multiplying the counted number of pixels per division by the pixel size on the sensor plane and dividing by the actual distance of the divisions on the slide. An example calculation is performed below on a lens of approximately 10x magnification:
Calibration slide with 50 um divisions
Camera with 6.5 um pixel size
Counted 72 pixels per division
Magnification = (6.5*72)/50 = 9.36x