Rolling Shutter in iPhone
Why do you see the individual blades of an airplane even though it is rotating at a very high speed? It is because iPhone’s camera lens is based on ‘rolling shutter’.
Rolling shutter (also known as line scan) is a method of image acquisition in which each frame is recorded not from a snapshot of a single point in time, but rather by scanning across the frame either vertically or horizontally. In other words, not all parts of the image are recorded at exactly the same time, even though the whole frame is displayed at the same time during playback. (Source: Wikipedia)
Thus, the resulting effect is that you can see the individual blades of the airplane when you record using devices using rolling shutter.
Blades of an Airplane (Recorded using Camera Plus Pro)
There isn’t any physical shutter in an iPhone or similar recording devices. It is just called that as a convention (something similar to a movie camera having a shutter moving across frames). In digital video, the rolling shutter effect is the result of the way a CMOS sensor is read. CMOS sensor doesn’t captures the entire frame at one go but instead information is read line by line of each frame, i.e. top to bottom. The video frame rate (fps) also depends on the quality of recording and also if the device is handheld.
CMOS sensors capable of higher frame rates than 30 frames per second (and not just through repeating frames) will exhibit less rolling shutter effect because their sensors have been designed to read faster. This limitation is removed in high-end DSLR cameras.
~ Saurabh
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Leica D Lux 4
