Can you help - Extended processing times for long exposures

18/09/2007 by paul

I've been trying to find the answer to a question posed by a customer recently, but have so far not been able.

Whenever this person takes a long exposure shot (which he is inclined to do regularly as he's an astronomer) the camera seems to take an equal amount of time to process and write the image to memory as the exposure time. I.e. a 3-minute exposure takes a total of 6 minutes to take; a 15-minute exposure takes 30 minutes; etc.

Writing to the memory card takes a fraction of a second (there is still only a sensor's worth of information to write, right?), so what's causing the extra delay?

My theory is that the camera uses a second shot of equal duration, but with the shutter closed, to apply a fixed-pattern noise reduction filter to the final image. This works by creating what should be a blank, black image to identify any noise artefacts, which are then subtracted from the final image.

He first noticed this on a Panasonic compact camera, but the same occurs on his new Pentax K10D. Can anybody tell me (and him) why? Please post your comments below. Thank you.

Previous comments to this article:

alternatively, do the NR on the computer with Noise Ninja or something similar. there are a few free ones floating around that do a stellar job. -j Julian (24/09/2007 6:07:00 AM)

turned the NR off and yea instantaneous(almost)processing.thanks all. robert (20/09/2007 11:40:00 AM)

Thanks for your responses. It's typical that the noise reduction (NR) may be the culprit exactly for the kind of shot (long exposure, dark background) that you need NR for! Robert, please let us know how you go with the NR turned off. Thanks. paul (Camera-Warehouse) (20/09/2007 10:53:00 AM)

yep youre on the right track - its the in-camera long exposure NR. on the D70 series cameras, you wont get 3fps in some exposure settings unless you disable it. the customer should try take the same photo with the long exposure NR option OFF and should notice a massive improvement in processing time. card speed will affect write speeds but shouldnt take that long anyway.. a K10D is what.. 10MP? each file, since it is mainly black, shouldnt take >1minute to write - even to a standard card. hope this helps - everyone's on the right track though. -j Julian (20/09/2007 2:02:00 AM)

g-day i've been shooting jpeg at the highest resolution with the panasonic(8mp) and pentax k10d.i'm using a sandisk 2.0 gb card. robert (19/09/2007 9:31:00 PM)

Hi there. I have taken a few longer exposures (on my K10D) and do notice that it takes longer to process (10 secs. Max) but no where near the times being described here. What SD card is he using? Is he shooting raw + jpeg ? P. Paul (18/09/2007 8:29:00 PM)

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Can you help - Extended processing times for long exposures