Digital Optical Comparator vs. Traditional Optical Comparator

Digital Optical Comparator vs. Traditional Optical Comparator

Digital Optical Comparator vs. Traditional Optical Comparator

Optical comparators are innovative tools used throughout manufacturing applications to inspect, measure, and compare the specifications of various manufactured parts. These machines use high-quality lenses and mirrors to magnify a component’s silhouette onto a screen and allow for an in-depth examination, checking for defects and inaccuracies.

Optical comparators are available in both traditional and digital configurations. Manual comparators are straightforward and valuable in smaller applications but lack the efficiency and strength to keep up with large-scale production cost-effectively. These tools can only produce 2D renderings of simple parts one at a time, making them quite labor-intensive.

Instead, more operations are turning to advanced digital optical comparators for streamlined work and enhanced accuracy.

Digital Optical Comparator vs. Traditional Optical Comparator Infographic

What Are the Benefits of Digital Optical Comparators?

Digital optical comparators allow professionals to obtain precise and dependable measurements of their products, resulting in higher-quality production output. They use high-quality digital cameras, sophisticated software, and unique lighting techniques to analyze simple and complex parts, complete with practical 3D capabilities.

Other benefits of digital optical comparators include:


Digital optical comparators are highly accurate devices delivering precise measurements and comparisons. Using advanced digital image processing and innovative computations, these systems can make corrections to enhance overall image quality. They can correct 2D non-linear distortion while performing other enhancements like sharpening edges and reducing noise to create a high-quality image.

While many traditional tools use templates and overlays, which tend to distort and stretch over time, these machines work with existing CAD plans for precise part comparisons. Digital optical comparator software also features sub-pixel edge detection technology to locate edges between pixels for ultra-precise results with minimal human error.


Digital tools streamline quality control and inspection procedures. They are quickly installed within various environments, allowing operators to incorporate them easily directly into their operations. Their small footprint optimizes floor space, and their mobility supports fast and efficient inspections throughout your location without needing re-calibrations in-between.

Digital versions use lenses with much larger depths of field, allowing the system to keep everything in focus while conducting inspections. This feature eliminates the need to refocus when continuously analyzing different sections of a specific part. Since this happens automatically, multiple parts can be examined without human participation, reducing labor costs while increasing throughput.

Due to their ease of use and convenience, these tools are widely used throughout numerous industries, such as:

  • Aerospace
  • Machining
  • Military
  • Power
  • Energy
  • Automotive
  • Telecommunications


Digital optical comparators are fully automated devices used with intuitive tools, such as the VisionGauge® patented CAD Auto-Pass/Fail™ and CAD Auto-Align™ systems from VISIONx, Inc. These tools make the VisionGauge® Digital Optical Comparator completely independent from operator to operator to increase the dependability and repeatability of the results. Here’s more information regarding these tools:

  • CAD Auto-Pass/Fail™: VisionGauge® Digital Optical Comparators deliver automatic reports, charts, statistics, and much more. This tool can determine whether a part is within tolerance, removing any operator subjectivity.
  • CAD Auto-Align™: This tool creates the best fit for the CAD by automatically aligning it to the part along the datums. It travels down the length of small and large parts, even across multiple fields-of-view, to collect imaging in different locations and provide information that matters.

Learn More About Digital Optical Comparators From VISIONx

VISIONx specializes in producing state-of-the-art automated imaging, visual inspection, and high-accuracy measurement solutions you can trust. We have created numerous digital optical comparator models capable of improving your site’s specific productivity and performance needs. With our patented VisionGauge® Digital Optical Comparator, you’ll ensure your products are within spec and avoid production flaws more easily than ever.

To learn more about our offerings, check out our selection of comparators or contact us online to connect with a specialist today.

Why Is the VisionGauge® Digital Optical Comparator More Accurate Than Traditional Optical Comparators?


Both the manufacturer and users have performed real-word tests with the VisionGauge® Digital Optical Comparator, showing that it’s significantly more accurate and repeatable than traditional optical comparators. With VisionGauge®, measurement accuracy, repeatability, reproducibility, and Gage R&R results are much better. Below, we will look into the main reasons why the VisionGauge® Digital Optical Comparator offers complete measurement equipment accuracy.

1. Completely Different Optical System

Traditional optical comparators magnify a small portion of the part being inspected onto a large projection screen. Let’s consider, for example, a 10X, 30″ comparator. A 10X magnification means this comparator will project a 3″ portion of the part onto its 30″ projection screen.

A traditional optical comparator does this using an optical system that is comprised of prisms, lenses, and mirrors. These are difficult to manufacture, and all have a certain level of defects. The large lenses used in the lower magnification traditional optical comparators — such as 5X — are especially difficult to manufacture and are the ones that suffer from the most inaccuracies and non-uniformities.

The VisionGauge® Digital Optical Comparator works differently. If we stay with this 10X example, VisionGauge® takes this same 3″ field-of-view, but instead of “blowing it up” to 30″, it reduces it to a roughly 1″ camera sensor. Lenses that do this are much easier to manufacture and are more defect-free. This means that right out of the gate, VisionGauge® starts off with a much better, more geometrically accurate image.

Superior Contrast and Image Quality

This fundamental difference in the optical systems of traditional optical comparators and of the VisionGauge® Digital Optical Comparator brings about another important added benefit. It’s well known that traditional optical comparators have very low contrast, which makes it even more difficult for operators to determine — subjectively — if a part is within tolerance.

Historically, attempts to address this contrast issue have involved putting a screen or curtains around the operator’s station to try to “dim” ambient illumination and allow the operator’s eyes to adjust. This low contrast issue with traditional optical comparators is related to the fact that they take the light from the smaller area being inspected and disperse it over a much larger projection screen — in our example above, light from a 3″ area is dispersed over a 30″ area.

Since it uses a completely different approach with a completely different optical system, the VisionGauge® Digital Optical Comparator doesn’t have to deal with any of these contrast issues. Because it collects the light from a larger area onto a much smaller camera sensor, VisionGauge® isn’t light-starved like traditional optical comparators can be. With VisionGauge®, there are no contrast issues to overcome and the overall image quality is superior.

Larger Depth of Field

It’s interesting to note that VisionGauge®’s re-thought optical system also provides another benefit — a much larger depth-of-field. This means that in most cases, everything is in focus “at once,” and the operator doesn’t need to continually refocus as they do with traditional optical comparators that have a very thin depth-of-field. This doesn’t contribute to an increased accuracy per se, but it certainly is a benefit from the user’s practical perspective.

2. Mathematical Digital Image Correction

So far, we’ve seen why the image that reaches VisionGauge®’s camera sensor is much better and more geometrically accurate than the one that reaches a traditional optical comparator’s projection screen. But understanding how accurate a standard optical comparator is compared to a VisionGauge® Digital Optical Comparator doesn’t stop there.

At this point, VisionGauge® is working with a digital image. There’s much that can be done when the image is in digital form, especially in the case of a high-contrast, super-high-resolution digital image, such as the one produced by VisionGauge®. VisionGauge® takes this better, more geometrically accurate image and improves it further.

Specifically, VisionGauge® uses a proprietary calculation scheme to carry out real-time full 2D non-linear distortion correction – directly on the live image video stream. These corrections eliminate the last remaining small geometric inaccuracies in the image, which even further increases the system’s final precision and accuracy.

3. Digital Image Processing

VisionGauge® can carry out digital processing of the image, which is another advantage over traditional optical comparators. For example, VisionGauge® can apply edge sharpening, electronic noise reduction, or any of the digital image processing and enhancement techniques that are now so widespread via the various cameras prevalent in everyday life.

4. Works Directly With the Part’s CAD Data (No Overlays!)

Traditional optical comparators use templates, Mylars™, overlays, or transparencies to compare a part to its drawing. These are printed out on transparent material that is then laid on the comparator’s screen. Of course, no printer is perfect, and printing errors reduce accuracy. Over time, this overlay material can stretch and distort slightly, which leads to a further reduction in accuracy.

The VisionGauge® Digital Optical Comparator compares a part to its CAD data directly. The CAD data is the mathematical description of the part. The data to which VisionGauge® compares the part is completely error-free — with VisionGauge®, there are absolutely no inaccuracies introduced at this stage of the process.


VisionGauge Digital Optical Comparators are idea for high-precision manufacturing

5. Powerful Sub-Pixel Accurate Edge Detection

With traditional optical comparators, pass/fail determinations are subjective and operator-dependent:  Multiple operators may need to consult each other for an opinion on if a part is good or bad. In comparison, the VisionGauge® Digital Optical Comparator uses sub-pixel accurate edge detection, making it ideal for high-precision manufacturing techniques. This completely eliminates operator subjectivity. Because its edge detection tool is sub-pixel accurate, VisionGauge® can actually locate edges accurately between pixels. This further increases digital optical comparator accuracy and precision.

6. Patented CAD Auto-Align™

With traditional optical comparators, the alignment of the overlay to the part and its datums are subjective. That can be a huge source of errors, and — obviously — results are operator-dependent.

The VisionGauge® Digital Optical Comparator has a powerful patented CAD Auto-Align™ tool that automatically aligns the CAD to the part along one or multiple datums or as an overall best fit. Results are extremely repeatable and completely operator-independent. This is a huge advantage over traditional optical comparators!

Furthermore, VisionGauge®’s CAD Auto-Align™ tool is not limited to the system’s field of view, or what the system “sees” at a given moment in time. It can actually travel down the length of long parts, capture images at different locations, and carry out a CAD Auto-Align™ over the entire length of the part. The automatic CAD-to-part alignment is not limited to small parts and can be carried out over large parts, to very high accuracy. That’s just about impossible to do on a traditional optical comparator, even in a subjective and operator-dependent fashion.

Profile tolerance Pass/Fail on the VisionGauge Digital Optical Comparator

7. Patented CAD Auto-Pass/Fail™

Finally, with traditional optical comparators, the determination of whether or not a part is in tolerance is subjective, and again, results are operator-dependent.

The VisionGauge® Digital Optical Comparator has a powerful patented CAD Auto-Pass/Fail™ tool that automatically determines if the part is within tolerance, either at point locations or across entire geometric entities. This provides much higher accuracy and completely eliminates operator subjectivity.

Additionally, VisionGauge®’s CAD Auto-Pass/Fail™ tool is also not limited to the system’s field of view. It can carry out a fully automated, high accuracy pass/fail determination over the entire length of the part, regardless of its size.

Summary of the VisionGauge® Digital Optical Comparator

The VisionGauge® Digital Optical Comparator is a drop-in replacement for traditional optical comparators that remains a general-purpose and easy-to-use system, capable of solving a wide range of inspection and measurement applications. These systems improve accuracy in manufacturing in general, including aerospace, medical, automotive, and a vast array of other industries.

Overall, the VisionGauge® Digital Optical Comparator represents a great technological leap forward from traditional optical comparators. It has innovative and up-to-date technology that, in many instances, completely does away with the inaccuracies that plague traditional optical comparators. As a result, the accuracy, precision, repeatability, and reproducibility of the VisionGauge® Digital Optical Comparator’s results are significantly better. Customer accuracy studies and Gage R&R studies have shown this time and time again.


Learn more about VisionGauge today.

Learn More About VisionGauge® Today

The VisionGauge® Digital Optical Comparator is your go-to choice for high measurement equipment accuracy. Contact us today to learn more about how our VisionGauge® systems can meet your needs for precision and accuracy in the manufacturing industry.

Download a pdf version of this article.

Announcing the Super-Extended Travel Configuration 500 Series VisionGauge® Digital Optical Comparator


The new VisionGauge® Digital Optical Comparator 500 Series Super-Extended-Travel Configuration is designed to inspect large and heavy parts while still delivering performance, reliability, and high-accuracy measurements. These systems have up to 60” of travel and support loads of up to 300 lbs!

This innovative configuration is designed to provide optimal rigidity and eliminate any mechanical deflections. Everything is optimized to allow the system to produce very accurate measurements of long and heavy parts.


500 Series VisionGauge® Digital Optical Comparator - Super-Extended Travel Configuration

The Super-Extended Travel Configuration is powerful and widely-applicable. In particular, the Industrial Gas Turbine (IGT) / Power Generation industry greatly benefits from the use of this system for inspection of fir trees / root forms on buckets.

Super-Extended Travel 500 Series VisionGauge® Digital Optical Comparator inspecting fir tree / root forms on buckets
Fir Tree / Root Form Inspection with the Super-Extended Travel 500 Series VisionGauge® Digital Optical Comparator

Download the data sheet, visit the product page, and contact us for more information.


Introducing VisionGauge®’s Patented “Tooth Checker™” tool

We’re happy to introduce VisionGauge®’s patented “Tooth Checker™” tool, specially adapted to check parts with teeth. This innovative new tool automatically locates, to very high accuracy, the crests and / or roots of the teeth and determines if they are within their tolerance band. It can also determine all other part characteristics, such as tooth pitch, thread depth, major & minor diameters, etc…

Bone screw teeth verification with the VisionGauge® “Tooth Checker™” tool
Bone screw teeth verification with the VisionGauge® “Tooth Checker™” tool

The Tooth Checker tool can verify that either crests, roots, or both, are in tolerance, using these crest & root points that the Tooth Checker tool has found, it can then automatically determine all other part characteristics:

VisionGauge Tooth Checker Nomenclature
Automatically check all part characteristics

This powerful new tool is perfect for quickly and accurately checking:

  • bone screws,
  • medical rasps,
  • gears,
  • fluted instruments,
  • threads & fittings,
  • and much more!


Click to view more information about the VisionGauge® Tooth Checker™, or download the application note.

Announcing the VisionGauge® Disk Inspection and Measurement System


The VisionGauge® Disk Inspection & Measurement System is the the ideal solution for automated, high-accuracy inspection & measurement of slots in turbine disks, both large & small. The system’s patented CAD Auto-Align™ & CAD Auto-Pass/Fail™ tools allow you to automatically check the slot profile, get deviations from nominal, etc…


VisionGauge Disk Inspection and Measurement System


Download the data sheet and contact us for more information.


New 5X configuration for 300-Series VisionGauge® Digital Optical Comparator


We’re pleased to announce the new 5X configuration of our 300 Series VisionGauge® Digital Optical


VisionGauge® Digital Optical Comparator 300 Series / Field-of-View Systems 5x configuration.

The 300 Series VisionGauge® Digital Optical Comparators are extremely cost effective Field-of-View
Systems that are ideal to inspect and measure smaller parts, very quickly. And the new 5X
configuration provides a wider field-of-view and a larger depth-of-field that extends the range of parts
that can be checked using the 300 series
. Specifically, the new 5X 300 Series machine can
accommodate parts up to 6.4” (diagonal, i.e. 5.5” horizontal x 3.3” vertical) and up to 4” in height. The
new 5X 300 Series VisionGauge® also has a very long working distance that provides 15” of
clearance between the part and the lens.


Like all of the other 300 Series machines, it has very high-resolution optics that produce a very
geometrically accurate image and it also includes three independent light sources that are all LED based
and computer-controlled: transmitted (i.e. back) illumination as well as both on- and off-axis
reflected (i.e. front) illumination. This allows the system to produce crisp, sharp edges and perform
beautifully even when working with hard-to-image materials (for example: shiny, reflective or even
translucent surfaces) and difficult geometries (such as deep holes).


The VisionGauge® 300 Series machines produce a stunning super-high resolution image to carry out
fine, detailed inspections. And the system’s crisp & clear image is displayed on a single super-high resolution


The 300 Series include all of the powerful VisionGauge® tools, including our patented CAD Auto-
Align™ and CAD Auto-Pass/Fail™ tools, for very fast automatic and operator-independent
comparison of parts to their CAD file, as well as VisionGauge’s® broad measurement toolset.


And because they are field-of-view machines and no motion is involved, the 300 Series
VisionGauge® systems are extremely fast. They can carry out hundreds of inspections and
measurements seconds after you’ve put the part down on the system. They can also accommodate
multiple parts at once.


All 300 Series systems have an intuitive software interface and are extremely easy to use. They can
be setup to be operated using the system’s barcode reader and joystick. They have built-in SPC
capability with charting & graphing and can automatically collect images and data. They also have
extensive data exchange capabilities.


The 300 Series VisionGauge® systems have a convenient desktop configuration, no moving parts
and no consumable parts. They provide many years of reliable service with minimal maintenance.
They are perfect for both the shop environment and the quality control lab. They are complete, ready-to-
run Windows-based solutions that are delivered network-ready and include on-site installation,
NIST-traceable calibration & training.


This information is available for download in .pdf format: 5X 300 Series VisionGauge Digital Optical Comparator Machine Announcement


Announcing the VisionGauge® Standalone Inspection & Measurement System


The VisionGauge® Standalone Inspection & Measurement System is the perfect drop-in solution for automated cells and automation applications requiring high-accuracy inspection. The system is widely-applicable and extremely general-purpose. All of VisionGauge®’s advanced inspection and measurement capabilities are available, including our CAD Auto-Align™ and CAD Auto-Pass/Fail™ tools.


The system includes a high-resolution optics with a large depth-of-field and a long working distance. It can be mounted in any orientation.

The VisionGauge® Standalone Inspection and Measurement System includes an inspection area connected to a remote workstation controlling the software and user-interface.
The VisionGauge® Standalone Inspection and Measurement System includes an inspection area connected to a remote workstation controlling the software and user-interface.

VisionGauge® OnLine’s Remote Program Communications feature is also included, making it easy to interface with a robot or other part-positioning equipment. The software possesses extensive communication capabilities (e.g. TCP/IP communication via Ethernet, digital I/O’s, etc…) to issue commands, load programs, retrieve results, process errors and messages, etc.


Download the data sheet and contact us for more information.


500 Series VisionGauge® Digital Optical Comparator Training – September 26th-27th, 2017

500 Series VisionGauge® Digital Optical Comparator Training Class
September 26th & 27th, 2017
(9 am to 4 pm on both days)


500-series VisionGauge Digital Optical Comparator training

A VisionGauge® Digital Optical Comparator 500 Series training class will be held at VISIONx’s facility (Pointe-Claire, Canada) September 26th & 27th, 2017.

The class will start with a short refresher of VisionGauge® Digital Optical Comparator basics and will quickly move on to a review of the latest software enhancements and then onto more advanced topics, including automated programs.

This is a very hands-on class and – as always – we are very happy to look into the specific challenges of your real-world applications with you.

The training will be in English. There is no charge for current VisionGauge® Digital Optical Comparator users and lunch is provided on both days. Participants are responsible for their own travel, lodging and other expenses.

Email [email protected] to sign up, or if you have questions, want for information about nearby hotels, assistance with travel arrangements, etc…
Sign-up closes on September 8th at 5 pm (Eastern Time zone).

New Horizontal Configuration for 400 Series VisionGauge® Digital Optical Comparators

400 Series VisionGauge® Digital Optical Comparators are now available in a horizontal configuration. These systems are state-of-the-art inspection and measurement systems in a compact desktop format. The systems feature a large measurement envelope (up to 12″ x 12″), 3 manual stages (X, Y, and Z), high-resolution precision optics, X/Y 0.25 micron resolution encoders, VisionGauge® OnLine software, and much more.

The 400 Series VisionGauge Digital Optical Comparator with manual stage motion in horizontal configuration.
The 400 Series VisionGauge® Digital Optical Comparator with manual stage motion in horizontal configuration.

Note that you can obtain an updated product brochure (with specifications, etc) in .pdf format.

Extended Travel 700-Series VisionGauge® Digital Optical Comparator featured in Modern Machine Shop

A new article about the Extended Travel 700-Series VisionGauge® Digital Optical Comparator has just appeared in Modern Machine Shop.

Larger Digital Comparator Model with Trunnion-Table Design

The 700 Series VisionGauge® Digital Optical Comparator 5-axis inspection and measurement system is the ideal solution for the automatic inspection of parts with complex geometries.
The 700 Series VisionGauge® Digital Optical Comparator 5-axis inspection and measurement system is the ideal solution for the automatic inspection of parts with complex geometries. The Extended 24" x 24" x 24" travel machine with trunnion configuration for big and heavy parts is shown above with a single monitor.

The article is also available in pdf format.