Optical Comparator - J&L Metrology Optical Comparator, Sales, Service, Parts, New and Recertified Optical Comparators - products

By: Vermont Precision  09-12-2011
Keywords: Lenses, Screens, Lens

How to choose what is right for your needs:

Below we’ve summarized some of the main items that should be taken into consideration when buying an optical comparator. Please feel free to contact us with any questions regarding sales, applications, or competitive products.

Step 1 – Is a horizontal or vertical light path model best for your application?

Horizontal light path Optical Comparators have a beam of light traveling horizontally across a work stage. This is the most common and versatile style of comparator and comprises more then 95% of comparator inspection applications. The horizontal beam is well suited for large and small parts and the work stage can accommodate a wide variety of work-holding tooling. Typical applications include milled or turned components, screw machine parts, plastic injection molded parts, threads, grooves, extrusions, large heavy parts and shafts to be held on V blocks or between centers. J&L Metrologies line of optical comparators can be configured to operate manually or under full CNC control. They can also be fitted with a video camera system to operate in tandem with the projection optics when configured as a Vivic Measurement System

Step 2 – What screen size and stage size best suits your application?

How large of a viewing screen should you get? How big is big enough?

The answer is based on the type of measurements you plan to make.

Measurement by comparison (with overlay charts or screen templates) can use the entire viewing screen. A larger screen means you can see more of the part at any one time, perhaps measuring many features at once with the same chart. Measurement by motion (with visual alignment or edge detection) uses the movement of the worktable assembly and screen rotation to measure the part. How large of a part you can measure is based solely on the overall travel of the worktable.

Field Of View



















Step 3 – What lens/lenses you will require?

Step 4 – Do I need a digital readout?

Step 5 – What options or tooling will be required for my Optical Comparator?

Repeatability and accuracy will suffer if the work piece is not properly and securely held. Work-holding is just as important when inspecting a component as when machining the component. Careful consideration should be given to tooling and to the surface on which you place your comparator. J&L offers a very wide range of standard work-holding solutions and our applications engineers will be happy to work with you to develop special work-holding as required. See our separate brochure for options.

Optical comparators come in an wide variety of shapes and sizes. Benchtop, floor model, in-line, side-screen, front screen, side-table. How do you know what type of system to get, and which options to specify? If you have questions – we have answers, Contact our sales team to

Benchtop or Floor Model?

Whether you choose a benchtop or floor model comparator may ultimately depend on the size and weight of the parts to be measured. Other factors to consider include space (floor models typically take up more space than benchtop systems), required screen size (benchtop systems rarely have screens larger than 14" or 16"), and cost (floor models are generally more expensive).

What kind of parts are being measured?

Benchtop models are smaller, lighter, and have lower load carrying capacity and measuring range than most floor model systems. Consequently, one usually finds benchtop comparators employed for measurement of small, lightweight parts such as plastic moldings, stampings, lathe work, etc.

Objective Lenses / Optics

Objective Lenses / Optics

Simple Reversed Optical System – As used on J&L CLASSIC series instruments
Simple reversed optic images that are upside down and reversed.

The smallest, simplest, brightest and least expensive optical system is referred to as a simple reversed optical system. In these instruments, an objective projection lens magnifies the object and the image is directed to the angled screen by a single mirror. The image is inverted (upside down) and reversed (left to right). The objective projection lenses are mounted on the outside of the instrument and 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. When using simple reversed optics, the front working clearance of the

lenses (the distance between the face of the lens and the part being inspected) decreases as the magnification is increased. Surface reflection options used on simple reversed systems will be oblique off-axis fiber optics or will incorporate a half reflecting mirror adapter mounted in front of or on the magnification lens. It must be noted that J&L has developed a series of magnification lenses that can be used in a 14” simple reversed optical system and that produce a fully corrected image. This series of lenses is the only exception to the reversed image description above. All of J&L's CLASSIC and TOPIC models employ simple reversed optical systems.

Simple Reversed Optical System – As used on J&L ICON series instruments
Images on machines with Erect optics are corrected top to bottom but reversed side to side.

An adaptation of simple reversed optical systems is the Erect optical system. This type of instrument is basically a simple reversed system with the addition of another mirror in the vertical optical plane. The second mirror flips the image top to bottom so that it becomes corrected in the vertical plane. This instrument has all of the advantages and disadvantages of the simple reversed system except that the instrument itself is not as deep as the reversed machine and the screen is vertical for a better viewing angle. All of J&L's ICON models employ erect optical systems.

Fully Corrected Optics – As used on J&L EPIC series instruments
Images on machines with Erect optics are corrected top to bottom but reversed side to side.

Fully Corrected optical comparators use an additional optical system, called a relay lens, to form an intermediate image which is in turn magnified by the projection lens. The final image is fully corrected, or in other words, erect and unreversed. An important benefit afforded by fully corrected optics is a constant front working clearance, regardless of magnification. This allows the inspection of large heavy parts and those with large diameters. Front working distances are as follows 14” = 6.7”, 20” = 7.4”, 30” = 13”, 50” = 24” . Another important benefit of the fully corrected optical system is that the surface reflection system travels coaxially down the projection path.

This allows for superb, bright illumination with less power consumed. It can also illuminate directly down inside of deep blind holes and slots. Due to the extra optics in relay lens systems, the magnification lenses are usually arranged in an internal turret, often motorized for convenience. It should be noted that J&L EPIC series instruments employ an adjustable telecentric stop fitted to the relay lens system. This adjustable stop performs the same function as the F-stop on a camera. The operator can increase focus depth of field by closing the stop or increase contrast by opening the stop. This is an important feature that can be used to reduce or eliminate the hazy unfocused area on grooves and notches. All of J&L's EPIC models employ fully corrected optical systems.


The closer an object is to you, the larger it appears. This is one of the fundamental principles of optics. The same is true for any optical system, whether your eye, a camera, or an optical comparator. But this can cause an error when measuring a three dimensional part, or if the image is simply a little bit out of focus. Why? Because adjusting the focus on a non-telecentric, simple optics system changes the distance between the part and the optics, and that changes the magnification. The effect is not that large (typically several thousandths of an inch measured at the part), but in today’s world of ever shrinking tolerances, you need to be as precise as you can.

Telecentric relay lens optics were developed by J&L METROLOGY and Eastman Kodak in 1945 to alleviate this problem. Here is a good example that shows the difference between non-telecentric and telecentric optics:


Keywords: Lens, Lenses, Optical Comparators, Optics, Screens

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Optical Comparator - J&L Metrology Optical Comparator, Sales, Service, Parts, New and Recertified Optical Comparators - services

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