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Video Extensometer Buying Guide: 12 Things to Check Before You Buy

Writer: Chris Thomas
Chris Thomas
3 days ago
10 min read

A video extensometer is one of the biggest accessory purchases a materials lab makes, and the right model depends on far more than megapixels. The best choice comes from your test standards, the accuracy class they require, how far your specimens stretch, how fast they break and the machine and chamber you test in. This guide walks through the 12 things to check before you buy, with worked sizing examples, real setup videos from our lab and links to every model in our UGC-VE video extensometer range.

New to non-contact strain measurement? Start with what a video extensometer is and our comparison of video vs. clip-on extensometers, then come back here to size a system.

Quick answer: the buying checklist

  • Standards and accuracy class: which ISO 9513 or ASTM E83 class do your methods require for yield, proof strength or modulus?

  • Field of view: will the gauge marks still be in view at maximum elongation, with margin?

  • Resolution vs. field of view: more megapixels lets one camera cover a longer view at the same accuracy class.

  • Sampling rate: fast tests and brittle breaks need a higher frame rate.

  • Number of cameras: single, dual and triple-camera or two-unit systems join views for long, high-elongation specimens.

  • 2D or 3D: stereo 3D measurement removes out-of-plane errors from thin, curved or moving specimens.

  • ASTM E83-optimized models: for labs that must document Class B-1 performance.

  • Chamber testing: working distance, viewing window, lighting and temperature limits of the camera unit.

  • Specimen marking and contrast: how you will mark specimens quickly and consistently.

  • Measurement types: axial, transverse (r-value, Poisson's ratio), multiple gauge lengths and necking.

  • Machine integration: analog, digital and software outputs to your existing frame and software.

  • Calibration and support: on-site verification, calibration plates and training.

1. Start with your standards and the accuracy class they require

Extensometers are classified by how small an error they hold over their measuring range. Outside the US the reference is ISO 9513 (classes 0.2, 0.5, 1 and 2); in the US it is ASTM E83 (classes A, B-1, B-2, C, D and E). The lower the number or the earlier the letter, the tighter the allowed error. Your test standard tells you which class you need, and the requirement usually depends on the property you report:

  • ASTM E8 metals tensile: an ASTM E83 Class B-2 extensometer (or better) for yield strength; Class C is acceptable for elongation.

  • ISO 6892-1 metals tensile: ISO 9513 Class 1 or better for proof strength and yield; Class 2 may be used for properties measured at larger extensions, such as elongation after fracture.

  • ASTM E111 Young's modulus: typically Class B-1 or better, because modulus is measured over very small strains.

  • ASTM D638 plastics modulus: an extensometer meeting ASTM E83 Class B-2 at the strains used for the modulus calculation.

  • ISO 527-1 / ISO 527-2 plastics: an extensometer accurate enough for the modulus strain window (0.05–0.25 %) at your gauge length.

A video extensometer's accuracy class depends on the field of view it is set to: the same camera meets a tighter class over a shorter view. That is why every UGC-VE model page lists the measuring length for Class 0.5, Class 1 and Class 2 separately. For example, the UGC-VE-2105 5 MPx single-camera model covers 130 mm at ISO 9513 Class 0.5, 260 mm at Class 1 and 520 mm at Class 2.

2. Size the field of view for your maximum elongation

This is the most common sizing mistake. A video extensometer tracks marks on the specimen, so the final distance between the marks (plus a margin) must fit inside the field of view at the accuracy class you need. A quick rule:

Required measuring length ≈ gauge length × (1 + maximum strain) + 20–30 % margin

The margin covers grip seating, the specimen pulling out of the jaws slightly and the fact that the whole gauge section moves with the crosshead. Three worked examples:

  • Metals, ASTM E8, 50 mm (2 in) gauge, 30 % elongation: 50 × 1.3 = 65 mm, about 80 mm with margin. A UGC-VE-2101 (80 mm at Class 0.5) or UGC-VE-2105 (130 mm at Class 0.5) fits comfortably.

  • Plastics, ISO 527-2 Type 1A, 75 mm gauge, 50 % elongation: 75 × 1.5 = 113 mm, about 140 mm with margin. The UGC-VE-2105 at Class 1 (260 mm) or a UGC-VE-2109 9 MPx at Class 0.5 (220 mm) covers it.

  • Rubber, ASTM D412 Die C, 25 mm benchmarks, 800 % elongation: 25 × 9 = 225 mm, about 280 mm with margin. Choose the UGC-VE-2109 (440 mm at Class 1) or the UGC-VE-2116 16 MPx (330 mm at Class 0.5, 660 mm at Class 1).

Our guide to gauge length selection for video extensometers across ASTM standards lists the gauge lengths behind the most common methods.

UGC-VE 4000 series video extensometer measuring strain during a tensile test

3. Resolution: trade megapixels against field of view

Resolution sets how long a field of view one camera can cover at a given accuracy class. Our single-camera models step up like this (ISO 9513 Class 0.5 measuring length):

Pick the smallest camera that covers your longest test at the class you need. Over-buying megapixels costs sampling speed (next point) and makes the system more demanding on lighting and PC hardware.

4. Sampling rate: match the camera to your test speed

Higher resolution means fewer frames per second at full view. Typical rates on our range run from 200 Hz on the 1 MPx models to 70 Hz on the 16 MPx models, and most models reach up to 1 kHz by reducing the view width (500 Hz on the ASTM-optimized models). Choose a faster camera when you:

  • Test brittle materials that break suddenly, where you want strain data right up to fracture.

  • Run high crosshead speeds or short tests that last only a few seconds.

  • Need a dense data set around yield, for example yield point elongation in steels.

For most metals and plastics run at standard rates, 75–200 Hz is plenty. For elastomers pulled at 500 mm/min, the larger field of view usually matters more than the extra speed.

5. Single, dual, triple camera or two units?

When one camera cannot cover a long or very stretchy specimen at the class you need, cameras are joined into one continuous view:

  • Single camera (UGC-VE-2100 and 4100 series): the simplest, most affordable setup for most metals and plastics.

  • Dual camera (UGC-VE-2200 series and 4100-D models): two cameras joined end to end. The UGC-VE-2205 covers 520 mm at Class 1.

  • Triple camera (UGC-VE-2300 series): for the longest views. The UGC-VE-2316 reaches 920 mm at Class 0.5 and 1,900 mm at Class 1.

  • Two-unit systems (UGC-VE-4200 series): two 400 mm units stacked into one view, for floor-standing frames and long specimens such as webbing, rope and geosynthetics.

Multi-camera systems are the usual answer for high-elongation films and elastomers, long gauge lengths and large specimens, where a single camera would have to drop to Class 2 to fit everything in.

6. 2D or 3D stereo measurement?

A standard video extensometer measures in the plane of the specimen. If the specimen moves toward or away from the camera, a 2D system reads that as strain. This out-of-plane error matters for thin films and foils that straighten as they load, curved or twisted specimens, specimens that neck or wrinkle, and tests through a chamber window. Our 3D stereo models use a matched camera pair to measure in 3D and remove it:

For full-field strain maps across the whole specimen surface, see our Vector 3D non-contact extensometer and the guide to the types of extensometers.

7. ASTM E83-optimized models for Class B-1

US labs that report modulus or must document ASTM E83 performance often want a system specified directly against ASTM E83. Our ASTM-optimized models use low-distortion optics and an ASTM-optimized camera:

8. Testing in a temperature chamber

Video extensometers are popular for hot and cold testing because nothing touches the specimen inside the chamber. Check these points before you buy:

  • Working distance: our models work at 300–500 mm from the front cover (extendable on request), which leaves room for a chamber and its door.

  • Viewing window: the camera looks through the chamber window, so the window must be clean, flat and free of condensation. 3D models help when the window adds distortion.

  • Camera environment: the camera itself stays outside the chamber and is rated for 5–40 °C and 30–70 % RH.

  • Lighting: the built-in blue LED light (465 nm) keeps contrast consistent; a polarizing filter can reduce glare from shiny metal specimens.

Our environmental chambers run from −80 to +280 °C, and the temperature chamber buyer's guide covers sizing the chamber itself.

9. Plan how you will mark specimens

Video extensometers track high-contrast marks: dots, lines or tape on the gauge section. Consistent marking is the single biggest factor in repeatable results, so plan it before the system arrives:

  • Marks must contrast with the specimen (dark on light or light on dark) and survive the test without flaking or smearing.

  • Gauge marks should sit at your exact gauge length; a marking jig removes operator-to-operator variation.

  • Shiny metals, transparent films and dark rubbers each need a different marking method.

Our gauge length marking tool places marks at standard gauge lengths in seconds, and the complete guide to sample marking for video extensometers covers every material.

Video extensometer sample marking technique on a tensile specimen

10. Check the measurement types and software you need

Beyond axial strain, a video extensometer can measure several channels at once from the same image. Decide which you need now and which you may need later:

  • Axial strain for yield, proof strength, modulus and elongation.

  • Transverse strain for Poisson's ratio and sheet-metal r-value (plastic strain ratio).

  • Multiple gauge lengths on one specimen, for example to report results to two standards in one test.

  • Necking and local strain to follow where the specimen fails.

  • Bend-line tracking for flexural tests.

Video extensometer measuring transverse strain for r-value

Software runs on Windows 10/11 64-bit (or Windows Server 2019/2022) with a perpetual license on a USB key, so there is no subscription to renew.

11. Make sure it connects to your testing machine

A video extensometer is only useful if your testing machine software receives the strain signal in real time. Our UGC-VE range outputs strain as analog (via D/A), quadrature pulse, DOLI Binary, MODBUS, HP Video, TCP/IP and RS232, plus a JSON and MRT API. That covers most modern controllers, so you can add one to the frame you already own. Ask for:

  • The controller model and software version of your frame, and which input (analog or digital) is free.

  • Whether you want strain-controlled testing (the controller uses the extensometer signal to control the crosshead).

  • Mounting: our units mount on a standard 1/4"-20 tripod thread or two M6 points; ask us about a bracket for your frame.

12. Calibration, verification and support

ISO 9513 and ASTM E83 both require the extensometer to be verified, typically on installation and then at regular intervals (most labs verify annually). Ask what verification is included at installation, how the system is checked between verifications, and what training is provided for operators. A calibration plate lets operators confirm the scale quickly before a test series.

Video extensometer calibration plate and marker

Which UGC-VE model fits your application?

Typical starting points (we confirm every selection against your specimens and standards before quoting):

Browse all 37 models in our equipment catalog or on the video extensometers page.

Video extensometer buying FAQ

Is a video extensometer accurate enough for modulus?

Yes, when it is sized for the job. Accuracy class depends on the field of view, so choose a model and view that meet the class your standard requires at the strains used for modulus, for example ASTM E83 Class B-1 or ISO 9513 Class 0.5 or 1.

How do I choose the field of view?

Multiply your gauge length by one plus the maximum strain you expect, then add 20–30 % margin. The result must fit within the model's measuring length at the accuracy class you need.

More megapixels or more cameras?

More megapixels extend one camera's view but lower its frame rate. Extra cameras extend the view without giving up speed or accuracy class. For very high elongation or long specimens, dual or triple-camera systems are usually the better choice.

Do I need a 3D video extensometer?

Only if your specimen moves toward or away from the camera during the test, as thin films, curved parts and some chamber setups do. For flat metals and plastics, a 2D system is accurate and simpler.

Can a video extensometer measure through a temperature chamber window?

Yes. The camera stays outside the chamber at 300–500 mm working distance and looks through the window. Keep the window clean and free of condensation, and consider a 3D model if the window adds distortion.

Will it work with my existing Instron, MTS, Shimadzu or ZwickRoell machine?

In most cases. Strain is available as an analog signal, quadrature pulse and several digital protocols, so it can feed most controllers. Send us your controller model and we will confirm the connection.

Video or clip-on extensometer?

Clip-ons are economical for fixed gauge lengths on metals and rigid plastics. Video extensometers suit soft, thin, high-elongation or hot and cold specimens, measure to break without risk to the device, and can measure several channels at once.

How often does a video extensometer need verification?

At installation and then at regular intervals to ISO 9513 or ASTM E83, typically once a year, plus quick checks with a calibration plate between verifications.

Get help sizing your system

Send us your standards, specimen types, maximum elongation, test speeds and testing machine, and we will recommend a model and field of view with the accuracy class you need. Request a quote or browse the UGC-VE range. Planning a full system? Read the universal testing machine buyer's guide.

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