Screw thread pitch: a telecentric test reporting less than 0.007 mm
The application-lab sheet reports less than 0.007 mm over a 19.34 × 16.21 mm field using a bi-telecentric lens and collimated backlight. The useful design lesson is how the optics produce a stable, high-contrast thread silhouette.
Stabilize scale and edge contrast before judging a tolerance.
Real camera capture
- Field of view19.34 × 16.21 mm
- Image2456 × 2058 px
- Accuracy (as tested)< 0.007 mm
- Working distance73 mm
Optics application-lab test sheet
What the camera saw
Cropped from the source test sheet; original test annotations are retained. Captures are not generated or enhanced. Drag a comparison slider, or open any image full size.
The challenge
Pitch, crest and root measurements need edges that do not move when the screw sits a little higher or lower in the fixture. With a standard lens, a part that is closer looks bigger, and the flanks of a thread blur where they leave the focal plane.
Front lighting makes it worse: the machined flanks reflect unevenly, so the edge the software finds depends on surface finish rather than geometry.
How it was solved
The test identifies the LS-VCM230-26 bi-telecentric lens and a green collimated backlight from the LS-VCL-26 family. Its source camera is 5 MP with a 2/3-inch sensor; the camera below is a current proposed alternative, not the source camera.
The lens reduces magnification changes with object distance, while the backlight puts the thread edges against a bright field. The reported field and image width correspond to approximately 7.9 µm per pixel (19.34 mm / 2456 px).
Why it works
- 1
Telecentric optics reduce perspective and scale changes within their specified operating range. Calibration and part alignment still matter.
- 2
Collimated backlighting limits edge wraparound and provides a useful silhouette for edge-based measurements.
- 3
The source reports <0.007 mm but gives no uncertainty budget, repeatability sample or edge-fitting method. Pixel sampling alone does not establish measurement accuracy.
Optics application-lab test sheet
Evidence you can inspect
The source camera capture shows the thread as a high-contrast silhouette.
<0.007 mm over 19.34 × 16.21 mm, at 2456 × 2058 pixels, as stated on the source sheet.
A reported application-lab result. It is not a guaranteed tolerance for the proposed camera or a production measurement study.
From image contrast to a production decision
What to validate on your part
- 01
Establish scale
Calibrate with a traceable artefact at the actual part plane and aperture.
- 02
Check repeatability
Repeat loading, rotate the part and vary height within the required fixture range.
- 03
Budget uncertainty
Include calibration, edge extraction, pose, thermal drift and part variation.
From the demo to your test bench
Parts in this setup
LensTested
LS-VCM230-26
Bi-telecentric lens for 2/3" cameras, 0.438x, WD 73 mm, C-mount (LS-VCM230-26)
Bi-telecentric, 0.438x, made for 2/3" sensors.
$999.00
In proposed setup
LightTested
LS-VCL-26-XW-Y
Collimated (telecentric) illumination, beam dia. 26 mm, length 124.8 mm (LS-VCL-26-XW-Y)
Collimated light matched to the lens's 26 mm field; the test used the green version.
$289.00
In proposed setup
CameraOur pick
MV-CS050-10GM(NPOE)
Hikrobot MV-CS050-10GM(NPOE) 5 MP GigE area scan camera, IMX264, Gen 2 basic version, Mono, Without PoE
Same sensor format as the test camera: 5 MP, 2/3", 3.45 µm, monochrome (2448 × 2048 px).
$819.00
In proposed setup
Camera test stationOur pick
LS-BT-XZ-G-6-6045
Camera stand with XZ adjustment and glass tray, height 600 mm (LS-BT-XZ-G-6-6045)
600 mm column, 600 × 450 mm breadboard, XZ adjustment, glass tray and two lighting holders as listed. Proposed bench fixture; confirm loads, travel and camera/lens clamps.
$359.00
In proposed setup
"Tested" identifies the part named in the source. "Our pick" is a proposed alternative or supporting part. Confirm colour, optics, controllers, power supplies, cables and mounting before ordering.
The set-up
| Camera (test) | 5 MP, 2/3", 3.45 µm pixels |
|---|---|
| Lens | Bi-telecentric, 0.438x, C-mount |
| Light | Collimated (telecentric) backlight, green |
| Working distance | 73 ± 1 mm (lens spec) |
| Depth of field | ± 2.3 mm @ F11 (lens spec) |
| Mounting (proposed) | LS-BT-XZ-G-6-6045 · camera test station with glass tray and two lighting holders |
Mount the optics with intent
The station is an optical test bench, with its two lighting holders included in the catalog listing. The 3D column and base follow the published height and footprint. Carriages, clamps and part supports are schematic: confirm camera screw pattern, lens support, light fasteners, permissible load and actual travel before ordering.
Complete the electrical system
This collimated light requires the specified constant-current driver configuration. Confirm current, colour, connector and power before selecting a controller; a general 24 V voltage controller is not a substitute. Camera cables and PC are separate selections.
Build this system
Start from this setup, adapt it to your part.
The configurator opens with this study's camera, lens, light and station picked. Swap any part, check fit and price, then buy or ask for a quote.
Camera and available lens CAD are published models. Lens and light envelopes use printed dimensions. The linked station uses its published base size and column height; carriage, brackets, fittings, parts and spacing are illustrative. Confirm load, travel, fasteners and clearances before ordering. Light paths explain the arrangement and do not simulate optical performance.
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Make the next trial specific.
Tell us the part size, smallest defect or tolerance, available working distance, material and line speed. Include what a good part and a reject look like.
About this case study: the photos and camera images come from the application laboratory of the maker of the lighting and optics we sell, imaged on the parts shown; your results depend on your part, camera and set-up. This is an application-lab study, not a LumaSpec customer deployment. Source figures are reported results; proposed components require a fresh trial. The 3D scene illustrates the arrangement and does not simulate imaging performance.