1DsII in camea noise reduction...

[shiato storm]

just after a quick answer here, with Noise Reduction set to 'on' should it take a second frame - after the shutter has closed - equal to the length of the exposure time (above 1s i think it is which is similar to the 1DII I also use), and then perform a dark-frame subtraction prior to writing to the card... or does it employ an alternative method meaning quicker writing to the card?
I thought it used the first method (equal length 'exposure' with shutter closed) but recently with NR set to ON, it's writing to the card almost as soon as its shot until near or at 30s, after which it seems to be taking the dark frame as originally expected...
Is the 1dsII's operation different in that respect?

 

[mho]

Some info - Taken from here http://www.imaging-resource.com/PRODS/EOS1DS2/1DS2A7.HTM

Noise Reduction System
The remaining exposure mode is Bulb, which simply allows you to take long exposures for unlimited periods of time, depending on the type of power source (With the new DIGIC II chip, Canon estimates a fully charged battery pack will allow for a 3-hour maximum exposure time, double that of the previous 1D and 1Ds; however the AC adapter allows for unlimited exposure times.) The 1Ds Mark II automatically employs a noise reduction system in exposures longer than 1/15-second (this function can be turned off through the Record menu when shot-to-shot cycle time is an issue). Most digital camera noise reduction systems use a "dark frame" approach, in which the camera shoots a reference frame the same duration as the exposure of the subject, only with the shutter closed, and then subtracts the resulting noise pattern from the captured sensor data to produce a final, reduced-noise image. Canon's CMOS sensor technology can apparently accomplish the fixed-pattern noise reduction processing right on the sensor chip itself, and so doesn't need to capture a separate dark frame to perform its anti-noise processing. As a result, the Canon 1Ds Mark II can capture long bulb exposures one right after another, without needing to wait in between to capture dark frames. This can greatly speed up long time-exposure photography, and would be especially helpful with the very long exposures required for astrophotography. To prevent any camera movement during long exposures (from holding down or releasing the Shutter button), it's best to work with the accessory remote control and attach the camera to a tripod. As was the case with the original EOS-1Ds, I was pleased to find that the noise reduction system worked even in Bulb exposure: The dark-frame noise suppression systems on most digital cameras I test are limited to timed exposures of relatively short duration.

In my testing, I found the Canon 1Ds Mark II's noise reduction system exceptionally effective. It won't work miracles with a very warm camera (image noise roughly doubles for every 8°C rise in temperature), but I rarely found any "hot pixels" in any of the bulb exposures I did, although I only tested it to roughly three minute exposure times. (If you do encounter any stuck pixels, I highly recommend Mike Chaney's Qimage Pro, a program with an amazing ability to remove spot noise without disturbing the underlying image.)

 

[shiato storm]

Good info. Cheers for that, looks like it doesn't need a d/f then