MeasurementWhat is an optical comparator (profile projector) and what is it used for?
The optical comparator is one of the most practical ways to verify small parts with shapes and contours. In this guide we explain what an optical comparator is, what it is for and which ones we carry from the Starrett brand.
What is an optical comparator?
An optical comparator, also called a profile projector, is an instrument that projects an enlarged silhouette of a part onto a screen. On that magnified image you can compare the part against a drawing or template, or measure its dimensions, angles and radii. It is like having a giant magnifying glass with a ruler, very useful for small parts with complex shapes that would be hard to measure by hand.
What is it for?
- Comparing against a template: the part's silhouette is overlaid on a scaled drawing to see whether it is within tolerance.
- Measuring contours, angles and radii: of small parts, threads, gears, inserts and cutting tools.
- Quality control: quickly checking batches of small parts.
The optical comparators we carry
We carry Starrett optical comparators, in benchtop and floor models, which differ mainly in screen size and capacity:
| Starrett model | What is it? |
|---|---|
| HB400 | Benchtop optical comparator (400 mm screen) |
| HD400 | Horizontal optical comparator (400 mm screen) |
| HF600 | Floor-standing optical comparator (600 mm screen) |
| HF750 | Large-format floor-standing optical comparator (750 mm screen) |
How to choose?
The choice depends on the size of your parts and your workload: for small parts and spot checks, a benchtop model (HB400/HD400); for larger parts or continuous use, a floor-standing model with a large screen (HF600/HF750). If you need to measure many dimensions automatically, you may be better off with a vision system.
Starrett optical comparators compared
These are the main specs of each model, taken from their data sheets. They help you choose based on the size of your parts and the type of work:
| Model | Type | Screen | X–Y range | Magnification | Stage capacity |
|---|---|---|---|---|---|
| HB400 | Horizontal benchtop | 16" (400 mm) | 400 × 150 mm | 10X to 100X (5 lenses) | 50 kg |
| HD400 | Dual lens, instant change | 16" (400 mm) | 400 × 150 mm | 10X to 100X (5 magnifications) | — |
| HF600 | Horizontal floor model, motorized axes | 24" (600 mm) | 500 × 200 mm | 10X to 100X (turret) | 150 kg |
| HF750 | Floor model, large format | 30" (750 mm) | — | 10X, 20X, 50X and 100X | 150 kg |
HB400, HD400 and HF600 have 0.5 µm resolution. Data is for reference; confirm the exact configuration with your advisor.
In summary
- An optical comparator projects an enlarged silhouette of the part onto a screen
- Used to compare against a template and measure contours, angles and radii
- It is ideal for small parts and complex shapes
- We carry the Starrett HB400, HD400, HF600 and HF750 models
Frequently asked questions about optical comparators
What is an optical comparator?
It is an instrument, also called a profile projector, that projects an enlarged silhouette of a part onto a screen to compare it against a drawing or measure its dimensions, angles and radii.
Does an optical comparator measure without touching the part?
Yes. It measures without contact: it projects the enlarged shadow of the part onto a graduated screen, which makes it ideal for small and fragile parts.
What magnifications do Starrett comparators offer?
The models we carry work with lenses from 10X to 100X. The HB400 and HD400 have five magnifications (10X, 20X, 25X, 50X and 100X).
Benchtop or floor-standing comparator?
For small parts and spot checks, a benchtop model (HB400 or HD400). For larger parts or continuous use, a floor-standing model with a large screen (HF600 or HF750).
Optical comparator or vision system?
If you need to measure many dimensions automatically, a vision system may suit you better. The comparator is more practical for comparing contours and checking batches of small parts.
Why buy your measuring equipment at NAT MAC?
We are a Starrett distributor, one of the most prestigious brands in the world of metrology, with more than 54 years of experience in the industry and ISO 9001 certified quality. We advise you on choosing the right equipment for what you need to measure.
- Starrett measuring equipment for dimensional and quality control
- Advice on choosing the right instrument for your part and process
- Hand tools, vision systems, optical comparators, laser measurement, granite and force testing
- Backed by ISO 9001 certified quality
Tell us what you need to measure and with what accuracy, and we'll recommend the right equipment. Request your free quote.
Sources: NAT MAC Measurement catalog; Starrett (metrology catalogs).
