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Can you help Extended processing times for long exposures

Posted 2/12/-1 at 10:00 AM

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.

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