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Measuring minimal and maximal microscope magnification and zoom ratio

Magnification ratio is one of many parameters to describe optical instrument – microscope in this case. Magnification ratio usually comes along with zoom range. These terms are often being misused. In this post I will measure zoom range and magnification ratio of monocular video microscope lens and stereo inspection microscope (Konus #5424) head.

Despite being different kind of optical instruments they have similar magnification ratios, so it’s fair to compare them.

Measurement

Let’s mount C1 camera on a lens and take some pictures of a known object at minimal and maximal magnification.

Two different rulers will be used:

Larger one is 50cm steel ruler

Smaller one is microscope slide 5mm with 0.01mm marks

I will use these pictures to measure view field dimensions. Also to be noted that video microscope uses 0.5x adapter tube.

Declared min magnification: (0.7x * 0.5) 0.35x -> 13mm(H) x 7.3mm(V)
Declared max magnification: (4.5x * 0.5) 2.25x -> 2mm(H) x 1.1mm(V)

Math – zoom ratio

Quickly calculate diagonal viewable image size at min and max magnification:

So stated magnification ratio is pretty legit. Good to know that manufacturer does not lie.

For reference I also measured trinocular microscope viewable image size at minimal and maximal magnification ratio. Please note that this time I measured rulers by eye and projected image is disc instead of being rectangular.

Declared min magnification 0.7x: D=33mm
Declared max magnification 4.5x: D=4.5mm
Zoom ratio: 33/4.5 = 7.3x

While specified parameters are the same magnification range is slightly wider than previous optical instrument.

Math – magnification

While we can’t measure stereo microscope magnification (don’t have projected image dimensions), it is pretty easy to calculate this parameter for lens mounted on a camera. To calculate this parameter we need to know used camera sensor dimensions. Good to know that C1 camera has known sensor dimensions.

To compare viewable area of both microscopes I provide you drawing.

While both compared microscopes have specified range of 0.7x-4.5x they have slightly different optical parameters. At a first glance video microscope has smaller view area, but it might be deceptive conclusions. Actually being C-mount it is suitable for larger sensors. How big? It might be between 1″ and 1/2″.