A part that moves during the exposure smears across the image. Enter the speed, the field of view along the motion and the camera's pixels in that direction, then the exposure time. The calculator returns the blur in pixels, how far the part travels during the exposure and the longest exposure that stays within the blur you allow.
How the motion blur calculation works
Use matching units: speed in mm/s, exposure in seconds (1 µs = 0.000001 s), field and pixel in mm. The calculator converts m/min, m/s, ft/min and in/s for you.
Worked example: a conveyor at 500 mm/s
- Pixel on the part: 100 mm / 2048 pixels = 0.049 mm.
- Travel during a 100 µs exposure: 500 × 0.0001 = 0.05 mm.
- Blur: 0.05 / 0.049 = 1.02 pixels, right at the usual limit.
- Longest exposure for one pixel of blur: 0.049 / 500 = 98 µs.
For gauging along the motion at half a pixel, the exposure drops to 49 µs. Each halving of the exposure halves the light reaching the sensor, so the light must be twice as bright, or strobed.
Typical speeds and exposures
| Application | Speed | Pixel on the part | Longest exposure for 1 px |
|---|---|---|---|
| Indexing table, part settled | 0 | any | no limit from motion |
| Slow assembly conveyor | 100 mm/s | 0.1 mm | 1,000 µs |
| Packaging line | 1 m/s | 0.2 mm | 200 µs |
| Bottling line | 2 m/s | 0.1 mm | 50 µs |
| Fast web or sorting | 5 m/s | 0.05 mm | 10 µs |
Exposures of a few tens of microseconds are normal for fast lines, but only with light concentrated on the part: strobe light controllers that overdrive the LEDs for the length of the exposure, and lights close to the part.
Strobing and overdrive
A strobe controller switches the light on only during the exposure. Because the LEDs are on for a small fraction of the time, many lights accept several times their continuous current for short pulses, which gives several times the brightness exactly when the camera needs it. The pulse length, not the camera's exposure setting, then decides the blur, so keep the pulse within the camera's exposure window.
The light controllers in the shop list their strobe and overdrive capabilities; the light's own data sheet gives the pulse current and duty cycle it tolerates.
When blur is not the limit
Very short exposures raise noise, because fewer photons reach each pixel. If a short exposure gives a noisy image even at full light, open the aperture a stop (and check the depth of field), use a larger-pixel sensor, or move to a line scan camera, which suits continuous motion because each line is exposed only for a fraction of a pixel's travel.
Next steps
Find the pixel on the part with the camera resolution calculator, then check that the frame rate the motion needs fits the link with the camera bandwidth calculator. The hardware trigger guide covers firing the camera at the right moment.
Questions
How much motion blur is acceptable in machine vision?
Keep blur under one pixel for most inspections: the image then looks the same as if the part stood still. Gauging and measurement along the direction of motion need half a pixel or less. Presence checks on large features tolerate two or three pixels. Blur only acts along the direction of motion.
How do I calculate the maximum exposure time for a moving part?
Divide the size of one pixel on the part by the part's speed, and multiply by the blur you accept in pixels. With 0.049 mm per pixel and 500 mm/s, one pixel of blur allows 0.049 / 500 = 0.000098 s, or 98 microseconds. Halve it for half a pixel.
What if the light is not bright enough for such a short exposure?
Strobe it. A strobe light controller pulses the LEDs only during the exposure, and many lights accept a higher current for short pulses, so the image gets more light without overheating the light. A brighter or closer light, a wider aperture or more camera gain are the other options, each with its own cost.
Does a rolling shutter camera blur moving parts differently?
Yes. A rolling shutter exposes the rows one after another, so a moving part is also skewed: its shape shifts by the speed times the sensor's readout time. Use a global shutter camera for moving parts, or a strobe that fires while all rows are exposing.