Optics
The optics are the heart of any comparator. When you think about it, the lenses in a comparator are really gages. Why? Because it is the image they form that is measured, not the part itself. And to make sure the image is accurate, optical quality (in design and manufacture) is critical.
You will find several different types of optics offered on optical comparators. Regardless of the type, however, the optics must be free of distortion (magnification change across the image), produce a flat field (image over the entire screen is in sharp focus), and have excellent resolution (sharpness of the image). Let us take a look at each type and discuss the relative merits of each.
Simple And Corrected Optics
The least expensive systems often employ simple optics. In this case, a projection lens magnifies the object and the image is directed to the screen by one or two mirrors. If one mirror is used, the image is inverted (upside down) and reversed (left to right). With two mirrors, the image is correct top to bottom, but still reversed. This second system is often referred to as corrected optics.
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Simple optic images that are upside down and reversed. |  |
Corrected optics are right top to bottom, but still reversed. |
In a simple lens system, changing magnification involves removing a lens from the front of the machine and replacing it with another. Some systems make this more convenient by providing a multiple lens slide or turret. In most cases, however, working clearance (the space between the part undergoing inspection and the optics) decreases as the magnification is increased. For three dimensional parts, this means that inspection at higher magnifications (50x - 100x) is generally limited to flat parts, prismatic parts with little thickness, or turned parts of small diameter.
OGP’s Focus is a unique corrected optics system, since it has a constant working distance and an internal lens turret.
Relay Lens And Fully Corrected Optics
Relay lens systems use additional optics to form an intermediate image (usually at 1x magnification) which is in turn magnified by the projection lens. The final image is fully corrected, or in other words, erect and unreversed.
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Images on machines with fully corrected optics are erect and unreversed. |
Another important benefit afforded by fully corrected optics is a constant working clearance, regardless of magnification. There is no limitation on part size or thickness due to the magnification selected.
Due to the extra optics in relay lens systems, the magnification lenses are usually arranged in an internal turret, often motorized for convenience.
OGP’s QL-20, QL-30, and OQ-30B feature relay lenses and fully corrected images.
Benchtop or Floor
