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One often reads again that the blade tip of a helicopter reaches supersonic speed (over 340m /s). In hover, this is not the case for this helicopter. The helicopter, Eurocopter BK117-C1 has a rotor diameter of 11m. During the exposure time of 1/100s the tips moved about 2.2 meters. The rotor moves at approximately 220m /s and turns nearly 7 times per second.
Due to the diffraction limit the diameter of a pixel is d = 2.44 · λ · B, where F-number B and the wavelength λ determined. With a typical value of λ = 555nm we obtain d = B · 1.3μm. The typical pixel size of today’s digital SLR cameras is about 5μm, so that we reached at f / 4, the theoretical limit. Digital Cameras have in some cases significantly smaller pixel sizes because they work with smaller image sensors.