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Magnification

The magnification of an object is the degree in which an observed object is enlarged or diminished through optical devices. It can be linear/transverse magnification or angular magnification. Magnification is written often as a number followed by a times “×” symbol as 2× or 3×. For example a 2× magnification of a circular object means the viewed object is twice the diameter and exactly four times larger in area.

When viewing a target directly with your eye, as in through a microscope, calculating magnification is fairly straightforward.  However, when viewing images remotely through a camera system and monitor, it becomes a little less straightforward as magnification is affected by many factors, here are some of the most important:

• Optical system focal length
• Imager size and resolution
• Object distance between detector or imager
• Monitor size and resolution

Given the number of input factors, it can be very complicated to calculate the overall magnification as viewed on a monitor. Some of the factors, such as actual distance to the target or object are often unknown.  As a result, magnification calculations are rarely used in remote visual inspection applications. However, in the event that the various inputs are known, the magification of an object as seen on a monitor can be calculated as follows:

Total Magnification_{as seen on monitor} = Magnification _optics x Magnification _video

where:

Monitor _diagonal = 685.8mm (using a 27" monitor")

Sensor _diagonal = 16.0mm (using a 1.0" CCD)

 

Mag_optics = Mag _adapter x  Mag _objective

Mag_optics = 1.0 x 1.0 = 1.0x

 

Mag_video = Monitor _diagonal / CCD or sensor _diagonal 

Mag_video = 685.8mm / 16mm = 42.9x

Total_mag  = 1.0 x 42.9 = 42.9x

 

Real Size Object _{as seen on monitor} = Length of Specimen _{as Measured On Monitor} / Total_Mag

Real Size Object _{as seen on monitor} = 100mm / 42.9x = 2.33mm 

 

Since the goal of calculating magnification is often to determine the size of a target object, alternative measurement techniques are typically used.  Here are a few examples:

• Pixel counting comparisons to a known length
• Stereo vision measurement
• Laser measurement

Related

• Depth of Field
• Imaging System Resolution
• Lenses