-Products offered by Bender Associates, Inc.

Formulas and Guidelines

We hope that the information which follows will assist you
in selecting the exact lenses or lens systems you need for
your applications. The data presented here is by no means a
comprehensive optical encyclopedia; rather it is a compilation
of basics intended to assist you in choosing the optimum optical
components and systems to meet your individual needs.

Points of Magnification

  • As numerical aperture increases, depth of focus decreases and resolution increases.
  • As magnification increases, field of view decreases.
  • As magnification increases, more light may be needed.
  • Magnification is developed in two ways: a. Different lenses create different magnifications at the camera. b. Camera and monitor combinations develop magnification between themselves.

Magnification at Camera

All cameras have a fixed sensor size. Thus, no matter how large
the image is at the sensor plane, the camera will "look at" only the
portion of the subject equal to the sensor size. Field of view is defined
as what the camera "sees." The lens, or lens system, of the camera
controls the magnification at the camera sensor. The lower this
magnification, the larger the field of view.

Magnification at Monitor

When the camera image is displayed on a monitor for viewing,
a further magnification takes place. The diagonal of the
camera sensor is expanded to become the diagonal of the monitor.
See chart on page 3.



	Example:            	

	A 2/3" camera is being used with a 9" monitor and the 

	11mm diagonal on the camera is being expanded to 

	9" (228.6mm) for a magnification of 20.8X.

In reality, because no manufacturer wants to have dark edges on the monitor, the camera is actually overextended in order to overfill the monitor, thereby guaranteeing no dark edges. There is no recognized industry standard, but a 5-10% increase in magnification with a resulting 5-10% loss of field can be assumed. It is in this area that a zoom lens provides freedom to implement the adjustment.

Useful Formulas



				Millimeters		Inches      

Resolution         	              
  in line pairs			(3000 x N.A.)/mm	(75,000 x N.A.)/in

Depth of field			+ .0005			+ .00002
      		 	        -			-
			        ________	        _________
       				   2			    2  
				N.A.		         N.A.
                  

Conversion Factors

	            

1 Inch		=25.4 mm      
1 Meter		=39.37 inches      
1 Micron	=0.001 mm 

Definition of Terms

Depth of Field - The distance over which acceptable image definition
can be maintained without refocusing.

Depth of Focus - The distance along the optical axis over which the
image is in focus.

Field of View - The area visible through a lens or lens system.

Magnification - A measure of the apparent difference in size
between the object and the image.

Numerical Aperture - A term representative of the largest cone or
number of light rays that can enter a lens system.

Resolution - The ability of a lens system to image closely spaced
points, lines, and object surfaces as separate entities.

Working Distance - The clearance or distance between the object
and the first surface of a lens system. Affects the users' ability
to image and manipulate the sample at the same time.

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Bender Associates, Inc.
Copyright 1998 - 2008.  All rights reserved.
Revised: February 18, 2010.

 

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