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Message: <blockquote data-quote="Dave_W" data-source="post: 113052" data-attributes="member: 9521">Two things that can add additional noise to long exposures, besides the obvious culprits, are 1) light leakage from seams and rubberized joints in the lens.2) Heat generated by the sensor, aka - thermal noise. Thermal noise is the #1 cause of noise in digital images. A long exposure will generate significant sensor heat and the higher the ISO is set, the higher the heating factor. Thermal heat is also a function of the sensor size, the smaller the sensor, the greater the heating. The best way to avoid thermal noise (actually the *only* way) is to shoot at the lowest ISO so as to increase the signal to noise ratio. Avoid the temptation to bump up the ISO on long exposures, leave it at 100 (or 200 depending upon your camera).</blockquote>