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Shine an incandescent light on a sheet of white paper, say a meter away (distance not critical). Be sure no fluorescent lights are shining on the paper. Have the incandescent warm up for at least a half hour.
Put the camera on a tripod, set up close to the paper so that only a small spot is imaged (1 to a few inches across). Set the lens to infinity so the image is very out of focus. Turn off auto focus. Record images as raw. If the tripod or configuration slips during the imaging sequence you have to start over.
Set the camera on manual at its lowest ISO setting. run some test shots increasing exposure until the camera indicates the image is saturated, even in the corners. Delete those images. This is your longest and starting exposure. It should not be longer than 2 seconds. If it is move the light closer.
Now start a series of exposures, doing two shots at each exposure and keep the f/stop constant. After two frames at the same exposure, shorten the exposure by 1/3 (or 1/2 stop), and take two more frames. Keep doing that until the histogram shows the intensity level is well below saturation, then do pairs every stop until you reach the shortest exposure time. That provides the series needed to determine full well capacity and test if the camera is photon noise limited (it should be).
Next is a series to test read noise. Again take pairs of images. In a relatively dark room with the lens cap on, take pairs of exposures at the fastest shutter speed (e.g. 1/4000 to 1/8000 second): a pair at each ISO (50, 100, 200, 400, 800, 1600, 3200). Note the temperature of the room.
Some cameras clip the low end, while others have an offset to the digital data so when there is no light on the sensor, the data properly record the noise. If the camera clips the low end data, single pairs of fast exposures in a dark room to determine read noise is not adequate. Pairs of exposures just above zero level are needed and the pairs subtracted, noise statistics measured and the statistics modeled, projecting to zero light level. Thus for each ISO, pairs of exposures that give light levels from zero to a few percent of maximum signal are needed. It is not necessary to go all the way up to camera saturation.
This series should take only 10 to 20 minutes, 30 to 40 minutes if the low end data are clipped at zero and you must take additional exposures.
If you still have time, some long exposure dark frames to test thermal noise. Again pairs of images, at ISO 800. The test should be done in a dark room with the lens cap on. You'll need a remote timer, e.g. a TC-80N3 for many Canon DSLRs. Do a pair at 30 seconds, 1 minute, 5 minutes, 10 minutes, 15 and 30 minutes. Note the temperature. If the timer does not work, or you don't have one, a pair of 30 second exposures at room temperature, iso 800, could at least indicate something.
It takes me about a day of work to analyze the data and write it up.
Home Page: ClarkVision.com
First published November 10, 2006.
Last updated December 27, 2007