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.
Two different rulers will be used:
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)
Quickly calculate diagonal viewable image size at min and max magnification:
SQRT(13^2 + 7.3^2) = 14.9mm SQRT(2^2 + 1.1^2) = 2.3mm
And now we can find zoom ratio:
Theoretical: (4.5*0.5) / (0.7*0.5) = 6.4x Zoom ratio: 14.9 / 2.3 = 6.5x
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.
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.
Sensor size horizontal: 5.07mm(H) Sensor size horizontal: 3.38mm(V) Sensor size diagonal: SQRT(5.07^2 + 3.38^2) = 6.09mm
Also let’s take into account that camera does not use full sensor.
Pixel dimensions: 2.2µm x 2.2µm (square pixels) Frame size: 1920 x 1080 True frame size horizontal: 1920 * 2.2µm = 4.224mm True frame size vertical: 1080 * 2.2µm = 2.376mm True frame size diagonal: SQRT(4.224^2 + 2.376^2) = 4.85mm
Now when we have source and destination image sizes let’s normalize them to have nice magnification ratio
Min magnification: 4.85 / 14.9 = 0.33 = 1:3 Max magnification: 4.85 / 2.28 = 2.12 = 2:1
Simplified animated illustration shows projected image size variations.
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″.