Multiple exposure
The multiple exposure is a phenomenon in the photograph . In chemical photography it can happen that several images are exposed on the same point of the emulsion , so that the individual images are superimposed to form a common image. In digital photography , the image sensor is exposed several times before it is read out and deleted. This effect can be brought about consciously, but is usually undesirable.
operation area
- Motifs recorded at different locations or times can be composed into one image. In contrast to the photo montage , the superimposed motifs in the picture are not opaque, but appear transparent. If desired, this effect can be prevented by using masks.
- The impression of an X-ray view can be created by superimposing a recording with and a recording without a cover.
- Movement sequences can be visualized by making several phases of a movement visible on an image.
- When using a pinhole camera , multiple exposures inevitably result from the extremely long exposure times.
- To illustrate the progression of lunar eclipses and solar eclipses .
- To increase deliberate blurring in artistic-experimental recordings.
technical realization
There are three methods of multiple exposure:
- When the shutter is permanently open (position B), the film can be exposed several times by triggering several flashes . This procedure is only practical in the dark, otherwise overexposure would be the result. This method is particularly suitable for the analysis of extremely fast motion sequences, e.g. B. in ballistics.
- The shutter is opened again for each individual exposure, but the film is not transported between the exposures and the recording chip is not read and erased. Cameras with automatic film transport must be set to an appropriate operating mode beforehand in order to suppress the film from being forwarded after each individual exposure. In cameras with manual film transport, the lock that is usually present to prevent unintentional multiple exposures must be removed.
- With shutter speeds in the minute range (e.g. pinhole camera recordings), multiple exposures always result as soon as the object moves and changes its position within the image. On the other hand, a fast-moving object (e.g. a moving car) is not captured on the film in the first place. Both effects can be desirable in this experimental photography.
Multiple exposure when scanning (Multi-Exposure)
When scanning slides, black and white film, and negative color film, multiple exposure can be used to produce high dynamic range (HDR) scans. The process called multi-exposure scans the original several times with different exposure intensities. The data are then calculated to form an image. In this way it is possible to achieve a significantly higher dynamic range, i.e. H. capture more details of the original.
