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05-28-2010, 04:32 PM   #1
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Time exposures with K-10D.

Whenever I need to make long exposures on my K-10D I'm amazed at the time it takes to show the review, (i.e. process the photo).
I frequently document art exhibitions of various kinds, always by the gallery/artists lighting. Sometimes these are darkly lit, if that's a proper description, and it's not unusual to be working at times like 15 or 30 seconds at f8, or in extreme cases, one or two minutes.
After completing say a one minute exposure, it always seems to take the same amount of time for the review to appear, and hence the wait- time necessary before the next exposure can be made.
It was very annoying recently, during a thunderstorm, to make a 20 minute exposure, and have to wait another 20 minutes before the next shot. By then the best of it had gone, so I got 2 shots, whereas with film, the next exposure can be made immediately.
Is this problem unique to the K-10D or is this common with all DSLRs? I've never ever heard anyone complain about it before. Could it just be my camera? Unlikely I would have thought, as it functions perfectly in every other way, (except for the frustrating back-focus problems, now finally sorted).
Can you enlighten me on this phenomena? Why is it never an issue for anyone else?
Thanks in advance if you can solve this one. And do the K-20D or K-7 suffer similarly?
Best regards,
Jan Dallas.

05-28-2010, 05:19 PM   #2
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Mine reacts the same way but I think that I can take another shot while the first is being processed....I will check that tonight actually.
05-28-2010, 05:40 PM   #3
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That should be what is called Dark Frame Subtraction happening.

Marc Sabatella says this:

What it does is take a second picture after the one you really took - the second one with the shutter closed (hence a "dark frame"). So you press the shutter button for a 5-second exposure, the camera spend 5 seconds takes a picture, then closes the shutter and spends 5 mores seconds taking a second exposure with the shutter closed. The idea is to see where that second pictures shows noise or hot pixels, which is really easy to do since it *should* be completely black - any pixel readng that isn't 0 is noise. Then the camera compares that pictures to the real one and uses the second as a guide to remove the noise and hot pixels in the first (I think it literally goes pixel by pixel subtracting the value in the second picture form the value in the first).

from this thread

In your Custom Menu there is an option for turning off the NR. That should "fix" your nuisance.

Models after the K10D don't allow this to be turned off for any exposure over 30 seconds, I believe. That is, this is one of the reasons people preferred this model to its successors.

edit:
I grabbed my K10D and took a 30 second exposure. Immediately after I could view the picture.

Last edited by xixco; 05-28-2010 at 06:27 PM. Reason: corrections
05-29-2010, 04:59 AM   #4
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I am one of those that attempts Infrared on the K10D. My longest exposure to date was an hour long exposure, and I could immediately see the picture after it was taken. Huge hot spots, but if was a fun project. Everything Xixco says is correct.

05-29-2010, 11:33 AM   #5
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xixco is right.
What is happening in your camera is so called dark frame substraction and it works exactly as described by Mark in xixco's quote.
As said, you can turn this feature off on K10D but that's the last camera to allow you to so.

Peter
05-30-2010, 02:05 AM   #6
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Is the noise much of a problem, is it possible\easy to run your own dark frame in post production?
If so does the dark frame need to be the same exposure as the image or will any dark frame suffice?

Cheers

G
05-30-2010, 10:08 AM   #7
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QuoteOriginally posted by GrahamD Quote
Is the noise much of a problem, is it possible\easy to run your own dark frame in post production?
If so does the dark frame need to be the same exposure as the image or will any dark frame suffice?

Cheers

G

You can do noise reduction in PP, using various third-party software, but I don't think that you can do the same sort of dark-frame subtraction that is done in camera.

The point of dark-frame subtraction is that the dark frame taken at the same time, with the same sensor, for the same duration, will have pure noise. Any noise in the dark frame should be the same as the noise in the actual image. In PP, you can't duplicate the dark frame, so you can't perform the subtraction. Other software noise reduction techniques are available, but not dark frame subtraction.

So, yes, I believe that only a dark frame taken under the same conditions, such as temperature, and for the same duration, will work. Conceiveably, a single dark frame taken before/after a photo session could be used in PP to do subtraction for all the images in the session. Unfortunately, the camera doesn't work that way. The dark frame isn't recorded. I suppose you could take one on your own, with the lens cap on, but I no of no software that will use that in the same way the camera does.
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