Monitor Magnification

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How do I calculate the magnification of my sample on the monitor?

Calculating the image magnification on a video monitor can be accomplished first by determining the optical magnification and multiplying that by the electronic magnification.

Optical Magnification - (Objective * Photo Eyepiece)

The objective expressed as 10x, 20x etc. and the Photo Eyepiece is the optical path magnification that leads to the video camera. Some typical sizes are 0.45, 0.60, 1.25, 2.5 etc.

Electronic Magnification - (Monitor diagonal size / Camera CCD diagonal size)

The monitor's diagonal size is usually expressed as 14", 15", 17", 19", 20" and 21", etc. The camera's CCD is expressed as 1/3", 1/2", 2/3" or 1". However, this is not the dimension we use. We need to use the diagonal dimension of the CCD expressed in inches. The table below represents the common CCD sizes and their diagonal dimensions in millimeters and inches.

CCD Size	Diagonal Dimension
CCD Size	Millimeters	Inches
1/4"	4.0	0.16
1/3"	6.0	0.24
1/2"	8.0	0.31
2/3"	11.0	0.43
1"	16.0	0.63

The formula is -

(Objective * Photo Eyepiece) * (Monitor diagonal size / Camera CCD diagonal size)

If you will be calculating the monitor magnification on a computer screen and are using a frame grabber in your computer, the formula is a little different. You need to take the frame grabber's image capture diagonal resolution and the VGA's diagonal display resolution into consideration. First, calculate the optical magnification the same way as above. Then calculate the electronic magnification as follows -

(Monitor diagonal size (Frame grabber diagonal resolution / VGA diagonal display resolution)) / Camera CCD diagonal size

The table below shows common VGA resolutions and their diagonal dimensions (we are making the assumption that the frame grabber's image capture resolution is 640 x 480). The multiplier column is the result of the frame grabber's diagonal resolution divided by the VGA's diagonal display resolution.

VGA Resolution	VGA Diagonal Resolution	Frame Grabber Diagonal Resolution	Multiplier
640 x 480	800	800	1
800 x 600	1000	800	0.8
1024 x 768	1280	800	0.63
1280 x 1024	1639.20	800	0.49

The complete formula is -

(Objective * Photo Eyepiece) * (Monitor diagonal size (Frame grabber diagonal resolution / VGA diagonal display resolution)) / Camera CCD diagonal size

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