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Debris finder, PolCor-2
15: The camera
How do you solve this to get the signal higher then the cameras readout noise? You have probably seen all of these night vision binoculars, the Russian's with the image intensifier. They have an internal valve which electronically amplifies the signal. That's one way to go, at the binoculars at least. Otherwise they have to much drawbacks to be useful to be used here.
Now there is a more refined method where the image light amplifying is built up into the CCD circuit. The technique is called EMCCD, Electron Multiplying Charged Coupled Device, in which an internal electric field detaches a burst of electrons for each detected incoming photon. That in itself gives no less noise but the signal comes up at a higher level so that the camera's read-out noise impact is reduced. The camera's dynamics is however reduced accordingly as the gain is increased. One of the manufacturers who have such cameras is Andor Technology and is also the camera Göran has chosen to this instrument.
Camera shown here mounted at the bottom of the instrument unit. Above the vents visible are the water connection for cooling.
This camera can be seen as a photon counter, it detects the individual photons. It may, however limit the range of wavelengths to achieve this. An impossible dream before, normal amateur CCD cameras feature a noise of 8 e- to 25 e-. The system's pixel scale mounted on NOT is 0.12" / pixel, with the option to install a Barlow lens with x2 or x3 focal extension.
Something that perhaps many people reacts to are the few pixels the camera have, 0.25 millions only. But for professional astronomers, it is not the number of pixel, it's the quality of the measurement it performs that are important. If the camera cost anything? Well, 30,000 Euro you have to pay for it.
Here the camera is disconnected from its mount on the coronagraph.