Cold camera, less noise? [duplicate]

Question

In electronics, one of the most significant sources of noise is heat, usually in the form of infrared radiation. Everything gives off infrared radiation, and the hotter something is, the more radiation it produces. This radiation is undoubtedly one component of the noise experienced by camera sensors.

At colder temperatures, objects give off less infrared radiation. Therefore, it would stand to reason that when a camera is used on the cold, say at -10F Farenheit, the sensor will be receiving less ambient infrared radiation from the camera internals than it receives when operating on a hot summer day at 85F. Is this effect noticeable in images?

Answer 1

You can set an exposure such as 1/30 of a second at f/11 and you can duplicate this exposure by using an aperture of f/16 at 1/15 of a second or 1/8 of a second at f/22. This practice is called reciprocity (my definition equal work for equal pay). The reciprocity equation is e=it (exposure = intensity of light multiplied by the allotted time of the exposure. The law of reciprocity is violated when exposure times range into minutes and hours. It will take considerably more exposure time for film base photography when super long exposures are utilized. We have learned to increase time more than the equation tells us, this is called reciprocity failure.

By accident, astronomers working at high altitudes on mountain tops in the cold of winter, discovered that films better adhere to the equation when the film is cold. This evolved into “cold cameras” whereby dry ice film holders cool the film and thus circumvent reciprocity failure. The same techniques are commonly in use when digital imaging replaced astronomical film. The digital camera does not suffer much from reciprocity failure but noise is greatly reduced and noise is especially devastating when high ISO's and long exposure times are employed.

Answer 2

Most of the noise in a digital picture is due to thermal noise. This is due to the random motion of electrons at the operating temperature of the camera, this is called Johnson–Nyquist noise and this is proportional to the square root of the absolute temperature. This means that changing the operating temperature from 20 C to -20 C will reduce the noise by slightly less than 8%. So, you have to cool the camera to extremely low temperatures to eliminate the thermal noise. In practice one uses liquid nitrogen cooled sensors for applications where extremely low noise levels are needed, see here for an example of such a camera sensor.

Another source of noise is due to the finite number of photons that will lead to some finite number of electrons in a photo-site. This leads to two sources of noise, the number of photons per unit time that hits a photo-site emitted from a constant power light source will fluctuate. If on average N photons will hit the photo-site during the exposure, then the fluctuation will be of the order of sqrt(N), this means that the relative fluctuation scales as 1/sqrt(N). So, the lower the intensity of light, the more important this source of noise is.

Another effect leading to noise is due to the stochastic nature of the interaction of photons with electrons. The same number of photons hitting a photo-site will not always lead to the same number of electrons being moved into the photo-site. The net effect of the finite number of photons releasing a finite number of electrons then leads to a net amount of noise, which is called shot noise.

Shot noise is the dominant noise source in pictures taken by professional liquid nitrogen cooled cameras like those of the Hubble space telescope, it doesn't play a role in ordinary digital photography where it is always swamped by thermal noise.