Unwanted visual artifact — trailing images during fast camera movement, motion blur blur or faulty sensor readout in digital. Problem, not effect.
During fast pans or zooms, double contours suddenly appear—shadow copies of objects trailing the main image. This is the classic ghost image, and it annoys every DoP who struggles with it. It arises through several mechanisms: With analog film, a shutter opening that is too short during camera movement leads to individual image areas not being fully exposed. With digital—where we almost always work today—it occurs due to faulty rolling shutter readout or sensor lag. The chip releases pixel information with a delay when the camera moves; the image cannot keep up fast enough.
Practically, you see this especially during fast pans or during Steadicam use on straight paths. A window frame floats alongside the main subject—looks like a bad afterimage. With high-frequency movements—such as objects zipping through the frame—the sensor can no longer keep up and throws ghosting artifacts. This is particularly noticeable at 24p or 25p than at higher frame rates because the temporal resolution is lower.
Remedies: Longer exposure times (open the shutter angle)—then the motion blurs evenly instead of doubling. Move the camera slower or ramp the movement—smooth acceleration instead of jerks. With digital, it often helps to adjust the sensor readout speed or increase the frame rate. Some cameras have a global shutter, which doesn't have this problem—but that's expensive. Lenses with better optical resolution also help: ghosting becomes visible when the sensor can no longer resolve clean edges.
Don't confuse this with motion blur or rolling shutter effects, which may be desired under certain circumstances. Ghost image is an error—it needs to be removed. It's hardly correctable in post-production. So it's better to avoid it on set: test takes, slow movements, adjust shutter, choose the right frame rate.