This is a sequence of unretouched shots taken with a Kodak DC-120 camera to show the effect of long exposures in low light conditions. The shots are of late twilight sky with planets in a line. The camera using a 16s exposure sees almost as well as the human eye but tends to colour casts when underexposed.
|1 second time exposure||2 seconds time exposure||4 seconds time exposure|
16 seconds time exposure
My southern horizon is not ideal with an HPS and a Mercury street lamp clearly visible in winter. It is better when the trees are in leaf. The garden lighting can be subdued.
|8 seconds time exposure||16 seconds time exposure|
These are unretouched images taken with a DC-120 in deep twilight to show the sensitivity of the camera and the colour casts which occur on underexposure. Most notably that 4 stops under exposed is entirely greenish, whilst 3 stops under exposed is lacking blue and so appears orange. The other exposures have reasonable colour balance but show hot pixels and the warm corner leakage in the CCD chip at top right. These effects can be corrected by taking a dark frame for the same exposure with the lens cap in place. Thermal effects are inevitable in an uncooled CCD. I like the Kodak cameras because they permit long exposures. Some makers do not allow this flexibility.
Despite the problems with long time exposures the camera is almost as sensitive as the human eye in low light conditions provided the subject will stay still for 16 seconds, and the artifacts can be removed by taking a dark frame exposure under the same exposure settings with the lens cap on. A constellation shot of Orion (approx 80kb) using this method gives a better idea of how sensitive the camera is to faint stars. More modern cameras are slightly better provided they have a fast lens and permit time exposures.
There are plenty of other sites which show what other cameras can do. Some modern cameras even provide internal dark frame subtraction and noise suppression.