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08-23-2012, 01:33 PM   #1
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K-7 RAW internal processing after shot

Hi!

Intro: Pentax user since more than 30 years, digital since *istDL, K-10, now K-7 and several shirt pocket minis.

Question: I just shot a 45 minute night sky bulb (RAW). Stopped it with remote and now, since at least have an hour a ticking sounds comes from the K-7.

WHAZZIT???

Any help very appreciated!

Best,

Alexander, a.k.a. Highcloud

08-23-2012, 02:52 PM   #2
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It's called DFS Dark frame subtraction and you can't turn it off on K-7.
After a shot of 30sec or more I takes another shot of the same duration and "subtracts" from the original to reduce noise.

It's either a great feature or really annoying. You can decide.
08-23-2012, 07:42 PM   #3
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It's on page 92 of the manual "Slow Shutter Speed NR" which is option 18 in the custom menu.
As Steve said above, unfortunately, even if you turn it off, it will turn back on automatically if you use a shutter speed longer than 30 seconds.

Two solutions:
Use your K10d for long exposures - professional astronomy sensors are all CCD (like the K10d) anyway!
Use registax and combine a series of 25s long exposures into a single image.

Good luck!
08-24-2012, 07:31 AM   #4
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Hi to Down Under from Austria! (Now I know why the replies came so quick).

Thanks for the quick replies. I guessed that the K7 is working on something but the noise, the continued clicking, keeps me wondering.

Do you know if the is something moving?

Is the time for dark frame processing equal to the length of the shot?

Have already though of taking many short shots and have now downloaded Registax. Must search for a user guide for it now.

Cheers,

Highcloud, a.k.a. Alexander

p.s. Have been a few times to Sydney and once - before the America Cup - in Perth... yikes, centuries ago...

08-24-2012, 01:09 PM   #5
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Yes, the DFS exposure is the same length as the original exposure.

Its taking another identical exposure, with the shutter closed. Any resulting image is pure noise. The assumption is that the original exposure contains the same noise as the dark frame. The camera then "subtracts" the noise in the dark frame from the original exposure.

That's why the dark frame exposure must be the same length as the original.
08-24-2012, 04:39 PM   #6
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With a K-5 (and maybe some others) you can turn that off. That wins you 45 minutes everytime
08-24-2012, 05:26 PM   #7
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QuoteOriginally posted by noblepa Quote
Its taking another identical exposure, with the shutter closed. Any resulting image is pure noise. The assumption is that the original exposure contains the same noise as the dark frame. The camera then "subtracts" the noise in the dark frame from the original exposure.

That's why the dark frame exposure must be the same length as the original.
Actually it subtracts fixed-pattern noise which results from differences between the sensitivities of the individual pixels. If it were just random noise then subtraction wouldn't help.
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