Hello Don, The longer the sensor is on, the more thermal noise that is generated. So the second frame may record the thermal noise and remove that from the first exposure. This would give you a cleaner black image. The assumption the camera can make is that the second exposure is supposed to be pure black, so anything that shows up otherwise should be considered noise and can be removed from the first frame.
HTH, -- Bruce Friday, November 18, 2005, 9:42:00 AM, you wrote: DW> Okay. So I make my exposure with no DW> light. Then, automatically, the camera DW> makes another. The second would be the DW> same, since the first was taken with DW> absolutely no light; one is subtracted DW> from the other -- leaving what? The 80 DW> second exposure -- by the way -- was the DW> only one showing a noisy background that DW> might have been a nuisance; the others DW> were remarkably good. Maybe 80 seconds DW> is too much for the noise reduction routine? DW> This experiment was not done for me. I DW> will never use 1600 for serious things DW> and the exposures will always be less DW> than a second or two. A friend in DW> Oklahoma is planning to buy his son a DW> digital camera for Christmas and asked DW> me to do this test. DW> By the way, the new camera has not yet DW> arrived. The agents are waiting for a DW> shipment and will send it next week. I DW> am to send this one back in the same DW> box. The six volt battery has been DW> running the camera since I mentioned it DW> had arrived and reads 5.8 volts. The La DW> Crosse charger, which arrived yesterday, DW> is trying to bring back a set of NiCads DW> to life that may be beyond resurrection. DW> They were almost new (unused) but a few DW> years old. DW> Don DW> [EMAIL PROTECTED] wrote: >> The camera's noise reduction software is telling it to make >> multiple exposures. It takes quite a while to complete that process. >> Paul >> >> >>> Hi all, >>> >>> Today I did an experiment to check noise >>> at ISO 1600. I capped the lens, put the >>> camera in a black bag and made a series >>> of exposures 20, 40, 60 and 80 seconds. >>> But this is the interesting bit: >>> >>> After the first exposure the shutter >>> wouldn't trip a second time. I took the >>> camera out of the bag and saw the egg >>> timer was displayed. It was almost a >>> minute before it disappeared and the >>> camera was back to normal. This happened >>> after every long time exposure. Does >>> anyone know why this should be? Why >>> should the buffer unloading itself to >>> the card, or whatever it is that is >>> happening, take so long to complete? >>> >>> Don >>> -- >>> Dr E D F Williams >>> _______________________________ >>> http://personal.inet.fi/cool/don.williams >>> See feature: The Cement Company from Hell >>> Updated: Print Gallery -- 16 11 2005 >>> >> >> >>
