Motion Blur and Safe Shutter Speed

Features

• Two safe-shutter figures: the classic 1 / focal length and a pixel-level one
• The pixel-level figure uses reference pitch divided by the actual pixel pitch, so denser sensors need a faster shutter
• Blur computed from angular speed: how many pixels the current shutter smears
• The shutter needed to keep blur under one pixel, rounded to a standard step
• Separates motion across the frame, at 45 degrees, and along the lens axis
• Pixel pitch from sensor width divided by horizontal pixel count
• Understands `1/500` and `0.002` as shutter speeds
• Everything runs locally and nothing is uploaded

How to use

1. Enter the equivalent focal length, sensor width and horizontal pixel count
2. Pick a direction and enter the subject speed and distance
3. Enter the current shutter speed to see the blur in pixels
4. Clear the checkbox to show the blur only

FAQ

Why multiply the 1 / focal length rule by a factor?

That rule comes from the film era and describes 135 format at roughly 6 to 8 micrometre pixel (grain) size. A 61 megapixel full-frame body has a pixel pitch near 3.8 micrometres, so the same shake spans far more pixels. This tool uses a reference pitch of 6 micrometres divided by the actual pitch, which makes the pixel-level safe shutter faster for dense sensors.

Why is a distant subject easier to freeze?

Because blur follows angular speed rather than linear speed. Angular speed is speed divided by distance, so the same car at 36 km/h crossing at 5 m and at 50 m differs by a factor of ten in angular speed and in blur. Double the distance at the same speed and the blur halves.

How is the blur in pixels computed?

The shift on the sensor is focal length times angular speed times exposure time, divided by the pixel pitch to give pixels. Pixel pitch is sensor width divided by horizontal pixel count, assuming square pixels with no gaps. A different sensor or pixel count changes the result.

Why does motion along the axis show no blur?

Along the axis means toward or away from the camera. That motion mostly makes the subject larger or smaller, with almost no lateral shift, so it produces almost no smear. Motion across the frame and at 45 degrees does.