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08-31-2010, 06:47 AM   #1
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K20D: DFS and Startrails

Hey, I'm new to the forums and after searching for a solution of my problems on 2 other Forums, Google and also by looking at this Forums thread I still haven't found anything; thus this thread.

With the K20Ds Interval option I thought that taking startrails would be pretty easy. I simply set up my tripod measured the exposure and set it onto 90x30secs to stack them afterwards, but noticed that the DFS destroys the basic idea real quick.

I've read quite much about startrails and how to stack the exposures and how folks tend to do it with the K7 and K-x. But with my K20D I can't get rid of the DFS that easily I suppose.
I want to ask at which point the DFS kicks in; I wasn't able to find that anywhere, in Hypermanual it seems to kick in at 6secs and same in Bulb-Mode.

So if I want to get rid of the DFS the only thing to do would be taking single exposures but the DFS does strange things to my images at times messing them up really bad as illustrated below. So I wanted to ask if there is any way around the DFS (like making only 28secs exposures which seesm to work with the K7) or if there is someway to actually get rid of it.

P.S. The time of the Exif is wrong but I have no clue why.

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08-31-2010, 06:57 AM   #2
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The K-7 has limitations whereby you cannot elect to turn off long exposure noise reduction (dark frame subtraction) with exposures of 30 seconds or over. The best option for users wanting to do star trails is to make many shorter manual exposures then stack them together. This is what I do.

The thing is, judging from the exif data, both of these look like one long exposure (770s) rather than stacked exposures?
08-31-2010, 06:59 AM   #3
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From https://www.pentaxforums.com/forums/pentax-dslr-discussion/39200-k20d-astrophotography.html - "Yes, it is a bummer that the K20D won't allow noise reduction to be turned off. Some are "getting around" this by putting camera on multiple exposure mode and taking 9 shots on a frame. If you set it to manual exposure and set shutter for 8 seconds or less (if I remember correctly) it won't go into noise reduction if set to auto noise reduction in custom function."
08-31-2010, 07:26 AM   #4
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Well, those images above were just meant to convey that I can't take single exposures do to that purple noise appearing randomly.

So, if I can't go above 7seconds which is a pity I would have to go with 99x7secs which would give me about 693seconds which isn't nearly enough to get nice trails. Or I would have to set up a 2nd (3rd / 4th / 5th and 6th) Interval shot with another 99 shots, but I assume that would be very difficult since I'll have to change some settings and thus minimally moving the camera which might cause the shots not to be exactly overlapping anymore.

Is there really no solution to this? I hate the fact that I paid so much for a semi-pro camera that won't let me switch of the DFS.

08-31-2010, 07:48 AM   #5
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try using the k20d border correcter for the purple noise.. it will help a lot

http://forums.dpreview.com/forums/readflat.asp?forum=1036&message=32705881&changemode=1

about the problem and the fix
08-31-2010, 08:56 AM   #6
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Well, this type of noise isn't caused by High Iso thus I don't know if Raw Border Corrector 0.9 would work. But I'll give it a try right away.
08-31-2010, 09:02 AM   #7
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Ok, tried it and it showed no visual effect at all. Single Exposures are pretty much impossible as it seems, I wonder if Pentax will implement an Off-Switch for the K20Ds DFS in the next firmware....
08-31-2010, 09:20 AM   #8
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QuoteOriginally posted by WordsOfFarewell Quote
Ok, tried it and it showed no visual effect at all. Single Exposures are pretty much impossible as it seems, I wonder if Pentax will implement an Off-Switch for the K20Ds DFS in the next firmware....
I hope so.

For the K-x, too!

I wonder what happens if you take the batteries out after the initial exposure.. does it write the first RAW file?

08-31-2010, 10:02 AM   #9
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I don't think this is a noise reduction issue... I think it's a sensor issue.

I've been told that most sensors heat up with prolonged exposures, and that is why noise reduction is applied over 0.3 seconds in the first place. Apparently this heat creates artifacts in the resulting file. That is why most newer cameras only let you take video clips that are x number of minutes.

Now, the k20d is a good camera, but it does not have anything close to a state of the art sensor. The noise is pretty bad at long exposures and high iso. I think your exposure times are simply asking too much of the k20d... and potentially a large number of other dslr's.

Maybe I'm wrong
08-31-2010, 10:32 AM   #10
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Well Nikon and Canon do actually allow long exposures without the DFS so did the K10D. But I mean all I want to find a way to take decent startrails with my camera, and even the K7's 28 secs exposure would be ok.
08-31-2010, 10:49 AM   #11
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Lots of people using lots of Pentax models have asked for "long exposure noise reduction" to be optional - I'm not holding my breath though. But Pentax would do a real blinder if they added this.
08-31-2010, 09:52 PM   #12
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QuoteOriginally posted by WordsOfFarewell Quote
So if I want to get rid of the DFS the only thing to do would be taking single exposures but the DFS does strange things to my images at times messing them up really bad as illustrated below. So I wanted to ask if there is any way around the DFS (like making only 28secs exposures which seesm to work with the K7) or if there is someway to actually get rid of it.
There used to be a trick with certain Canon cameras that had DFS that couldn't be turned off. Basically it worked out to be that after the main exposure was finished and the DFS exposure had started, to turn off the camera. The main exposure was on the card, but the DFS data is lost, and therefore not applied.

I don't know if this would work with the K20D, but it might be worth trying.
09-01-2010, 03:52 AM   #13
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Then I'd had to stand next to the camera all the 2 hours and do that 120 times. But I actually think I tried that and it didn't work. The camera shuts down everything else but the chip still does the DFS and shuts down the chip individually afterwards.
09-01-2010, 05:40 AM   #14
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QuoteOriginally posted by WordsOfFarewell Quote
Then I'd had to stand next to the camera all the 2 hours and do that 120 times. But I actually think I tried that and it didn't work. The camera shuts down everything else but the chip still does the DFS and shuts down the chip individually afterwards.
Well, you wouldn't do it for 30 second shots that you were stacking. If you were doing a two hour shot, you'd do it once.

But alas, it's a moot point.
09-01-2010, 06:36 AM   #15
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I don't have a k20D, but do you have a multiple exposure feature on the it? Can you set that, for say 5 of 6 second blended exposures, thus stacking those in effect (5*6=30s)? Can you use the multiple exposure feature with continuous shooting, an intervalometer or a timer?
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