RESOLUTION:

Resolution is the ability of the optical system to distinguish between two objects that are spaced close together.  The lens and CCD sensor form the heart of the machine vision system.  Illumination can also play a part in the ability of the system to "see" what is to be measured.  One measure of the resolution is called MTF (Modulation Transfer Function) which is a plot of contrast at different spatial frequencies.  A fence composed of equal but wide boards and spaces is easier to see than another fence with equally narrow boards and spaces, when seen from the same distance away.  Both the lens and the CCD sensor can each be tested alone, and their performance described in the form of the MTF curve.  The system resultant MTF plot is the product of the lens MTF and the sensor MTF.

The smaller the pixel width (height) of the CCD sensor, the smaller the objects that can be resolved.  For example, a 24 µM pixel CCD sensor will not be able to see small details in an image as well as a 3.5 µM pixel CCD sensor when used with the same lens.

The lens resolution (MTF) is determined by its optical design and manufacture.  If the lens has poor images (low MTF), then the product of Lens MTF  and CCD MTF will be lower than if the lens is closer to perfection.

For the tiniest features to be clearly seen, this product should be as high as possible.  Using a CCD with small pixels does not buy you much if your lens MTF is low.

Example 1:  CCD MTF = 0.4,  Lens MTF = 0.4  Resultant product = 0.16 or 16 % contrast (may not be useful).

Example 2:  CCD MTF = 0.4,  Lens MTF = 0.8  Resultant product = 0.32 or 32 % contrast (will probably be useful).

Example 3:  CCD MTF = 0.7,  Lens MTF = 0.8  Resultant product = 0.56 or 56 % contrast (will definitely be useful).

As you can see, if the lens MTF is higher, then the resultant performance is higher.  Gibson Optics 1X lenses are diffraction limited over all designed wavelengths, and at every point in the field at widest F stop (F/6), so the performance will be maximized with any CCD, but especially with small pixel CCDs.  Other lenses may not have enough MTF at higher spatial frequencies, and will not be able to effectively use the performance of small pixel CCDs.

When a lens is designed to be telecentric (at least in the object space), the ray bundles are parallel to the optical axis.  The result is that when the object is slightly out of focus (on either side of best focus), the centroid of each element in the object still lies on the same CCD pixels as they do when the object is in best focus.  While the sharpness of the object (its MTF) is less, the location of the object points remains constant.  If the lens is looking at objects that have "height", you would not want those parts of the object that are at different focal (Z height) planes to be shifted sideways (X or Y or both errors).  Most machine vision lenses are telecentric.

Double telecentric lenses offer the advantage that if the object is shifted along the optical axis with respect to the lens, and then the CCD camera is adjusted to the new best focus, the positional (X,Y) accuracy of the object points remains accurate.  If the CCD camera is adjust once and is fixed in place, and the lens plus CCD camera is focused as one unit, then the errors that may be caused by this will be constant.

Gibson Optics lenses are double telecentric so that whatever planes the object and CCD end up at (with respect to the lens), the (X,Y) postional accuracy if maintained.

For 1:1 (1X) magnification lenses that are truly symmetrical about the internal stop have no distortion.  However, the actual distortion measured may not be exactly zero due to manufacturing of the optical elements in the lens.  Gibson Optics lenses are manufactured to very high tolerances, and consequently have very low (close to zero) distortion.

http://www.schneiderkreuznach.com/pdf/div/optical_measurement_techniques_with_telecentric_lenses.pdf

http://www.schneiderkreuznach.com/knowhow/telezentrie_e.htm

http://www.schneiderkreuznach.com/knowhow/digfoto_e.htm

http://www.mellesgriot.com/products/machinevision/machinetutorial.asp

http://www.edmundoptics.com/techSupport/DisplayCategory.cfm?categoryid=18