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09-01-2010, 04:25 PM   #16
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QuoteOriginally posted by Nass Quote
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?
I tried the first which works. But it's still just 30seconds. Using the setting continuously doesn't work though. Which is a pity cause that would have been a way around this issue.

Anyway: this is what my 1 hour star trail looks like; the camera took a 30second shot each 55seconds (the DFS ate up around 25 seconds). You can clearly see the gaps. It seems that the DFS took longer every 5 shots though no idea why. :-|

I though about simply writing Pentax customer service an email about this hoping if some more people already did this they might actually fix this DFS crap in the next firmware update.

I also asked a friend of mine if I can use his Eos 50D for this stuff; it's a pathetic that I have to burrow stuff even though I have a good camera.

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Last edited by WordsOfFarewell; 09-01-2010 at 04:37 PM.
09-01-2010, 07:53 PM   #17
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Evening,

I too have a K20 and would like to get rid of DFS, but I live with it. There is a 99 frame limit on the capability in the camera body for ..... To get around this try something like this. It will trigger the camera's shutter for 400 cycles (even if the camera is turned off).You can also use "B"ulb mode for longer exposures - as long as you want, say 2 hours. Just be prepared for 2 hours of DFS (actually it will be less, there turns out to be a maximum duration, It is listed here on the Forum somewhere, in one of the threads...)

09-02-2010, 04:28 AM   #18
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Yeah, I already looked into this. And I guess I'll get one, my old cable release got lost somewhere in Norway anyway.

About the Bulb: the light pollution in this area, actually the next 100km around here, is so bad every single exposure would have an overexposed sky so that wouldn't work.
09-04-2010, 10:58 AM   #19
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Bought an external programmable shutter release now. Still it can't force the shut off for the nasty DFS. I guess the only hope that K20D users can hold onto is that Pentax actually finally brings out a firmware update finally adding an "off" option to the Noise Reduction for long exposures.

After my search on the net I found numerous photographers that were upset about this but none had a solution, not even some tech-freaks that might as well crack that thing and change the software, but people with so much insight are seldom to be found I assume.

09-04-2010, 01:36 PM   #20
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Fyi, found this on Flickr, also with a K20d. Your issues might also be due to your particular camera. That sort of banding in your first shots doesn't look like a happy camper to me.

09-04-2010, 01:47 PM   #21
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QuoteOriginally posted by WordsOfFarewell Quote
Bought an external programmable shutter release now. Still it can't force the shut off for the nasty DFS. I guess the only hope that K20D users can hold onto is that Pentax actually finally brings out a firmware update finally adding an "off" option to the Noise Reduction for long exposures.

After my search on the net I found numerous photographers that were upset about this but none had a solution, not even some tech-freaks that might as well crack that thing and change the software, but people with so much insight are seldom to be found I assume.
The DFS is impossible to turn off on a K20. Your banding is somewhat different than mine (I was getting heavy noise, in a striped pattern - you are getting color banding, but no noise in the image). After a couple of months of it getting progressively worse (especially with bracketing), I sent the body back to Pentax last Monday (actually dropped it off at their warranty repair facility - CIRS in Chandler, AZ) for warranty repair. Waiting for word back on what may be wrong with it. At least I have another 18 months left on the 3 year warranty that came with the body.

Also, take a look at this thread - there is a result that may look familiar...

I would also make some additional suggestions. Use ISO 3200 rather than ISO 200 (note you can also try using 6400 too). That will speed things up and gather significantly more light. Also, use the fastest f stop you have f4, or f3.2, f2.8 or what ever. On your first set you were using f6.7. Set the camera up, set focus to infinity, and then try some various times - 30 seconds, 1 minute, 5 minutes, 10 minutes. For longer star trails, you might need to trim the ISO a bit. Use a noise reduction utility to remove the noise from the images and clean them up a bit. There are a lot of things you can do here to help yourself with the equipment you have. It takes a bit of understanding of how things work, the limitation on your setup (and all cameras will have limitations of some type), the best way to work around them, and then applying the right post processing tools.

Also, take a look here ....


Last edited by interested_observer; 09-04-2010 at 03:12 PM.
09-05-2010, 05:16 AM   #22
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QuoteOriginally posted by Nass Quote
Fyi, found this on Flickr, also with a K20d. Your issues might also be due to your particular camera. That sort of banding in your first shots doesn't look like a happy camper to me.
Well, my camera only does that kind of Color banding sometimes and mostly random, I've taken some good trails though. But single exposures usually don't work because the light pollution where I live is to strong, as can be seen in the 10min exposure straight into the sky at only ISO400 and f2,8 posted below.

I guess the stronger the light pollution the more often the color bandings appear. But since the light pollution is so strong single exposures don't work anyway. At least not around where I live.


QuoteOriginally posted by interested_observer Quote
The DFS is impossible to turn off on a K20. Your banding is somewhat different than mine (I was getting heavy noise, in a striped pattern - you are getting color banding, but no noise in the image). After a couple of months of it getting progressively worse (especially with bracketing), I sent the body back to Pentax last Monday (actually dropped it off at their warranty repair facility - CIRS in Chandler, AZ) for warranty repair. Waiting for word back on what may be wrong with it. At least I have another 18 months left on the 3 year warranty that came with the body.

Also, take a look at this thread - there is a result that may look familiar...

I would also make some additional suggestions. Use ISO 3200 rather than ISO 200 (note you can also try using 6400 too). That will speed things up and gather significantly more light. Also, use the fastest f stop you have f4, or f3.2, f2.8 or what ever. On your first set you were using f6.7. Set the camera up, set focus to infinity, and then try some various times - 30 seconds, 1 minute, 5 minutes, 10 minutes. For longer star trails, you might need to trim the ISO a bit. Use a noise reduction utility to remove the noise from the images and clean them up a bit. There are a lot of things you can do here to help yourself with the equipment you have. It takes a bit of understanding of how things work, the limitation on your setup (and all cameras will have limitations of some type), the best way to work around them, and then applying the right post processing tools.

Also, take a look here ....

Thanks, I've read quite a lot about star trails and the problems of the K20D by now and I've tried almost everything that I could (including getting the phottix cable release) and nothing worked.

There is not much I can do, the higher the iso the more visible light pollution get's caught in the exposure same goes for the exposure time. So there is not much I could do about it, the only thing that would let me get decent startrails is either moving to a place with less light pollution (so single exposures would work as in Nass' post) or an off funtion for the DFS (which I still hope to find so I can take pictures around the area where I live) or different camera, which I can't afford. But I guess the next thing I'll try is my old Super ME although I don't really care about analog because I can't scan my negatives yet and don't have a 10mm equal for it.

Here the single exposure and the blended one I did yesterday night at 2am-4am.

You see the big difference in terms of captured light pollution.
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09-05-2010, 06:43 AM   #23
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I believe that you still have some studying to do in order to learn about what you are trying to do. Regardless of the camera you may be using, especially for astrophotography, you will probably need to do dark frame subtraction. DFS is a technique originated by astronomers to characterize their electronic sensors, and remove internal noise generated by them in the process of taking images. DFS can be done in a number of ways.

You can eliminate the source of the noise before it affects the image. Heat is the primary culprit. You can cool the sensor with various items like liquid nitrogen, but that really is not practical. Or you can take a "noise" image, by taking an image of nothing (with the lens cap on). That is essentially what Pentax does with DFS. You take your regular image, then if the shutter duration is over 9 seconds, it takes a "second" image, and then mathematically subtracts the value of each of the pixels of the second image from the first. The second image represents the mapping of the noise generated by the heat of the first image's processing.

The primary argument you have is when and how this is done. Pentax for the K20 does it after each frame automatically. Other camera manufacturers let you do it when ever, however this will lead to inaccuracies (taking too little noise or removing too much noise). The longer you wait to take the DFS frame, the more differences you will have. For instance if you take the DFS frame first and then 30 frames over say 5 hours, will the DFS frame accurately characterize the noise over all the rest of the images? How about taking it after wards. In the after case, the DFS will exhibit too much noise for the first few images. So every technique is a compromise to some extent. Actually, the process Pentax uses is the most accurate, however it may not be the most convent and may be a case of overkill depending upon use.

Not performing DFS would be the worst of all possibilities. An alternative would be applying some noise reduction, however the noise reduction algorithms are general in nature and not specific to your sensor. In this situation DFS would be the best. I wrote overkill previously in the sense that if your are out doing quite a few images in a row, it would be reasonable to probably do a DFS image every 7 to 15 frames, so that this could be used to subtract off the noise in post processing. However, you need to remember to actually take the DFS image, and then to actually use the DFS image afterwards to remove the noise.

With respect to light pollution, you can probably drive an hour or so (depending on where you live) and find a place that has potentially less light pollution. Here is a light pollution map...For the best star trails, you should also eliminate the moon by only going out on a moonless night.




Last edited by interested_observer; 09-05-2010 at 09:51 AM.
09-06-2010, 04:11 AM   #24
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Thanks for the insight. I should've mentioned that I would take a DFS shot afterwards of course as all the Canikon guys do it, so no DFS is out of the question of course. Sorry for that.

And that Pentax is actually doing something that makes sense I won't negate, still the K20D isn't a K-x so something aimed at people who may not have as much experience with photography, and all I ask for is an off-switch, not getting rid of the DFS entirely. But in the end it makes quite some sense to do DFS right after the shot at least after reading what you explained, still a manual option would be nice for this use for example.

On the Dark Sky Finder; I must say that is a handy application indeed. But around here (in the Ruhrgebiet/ Germany you won't find any space that is not totally lightpolluted). To bad though that there are no entries on that in the map.

And yeah, I'll go out either tonight or Wednesday which is new moon, but I'll still have gaps in the trails or to much light, since I don't have the money to spend to much gas on driving around, for I would have to drive quite some distances to get a single exposure.
09-06-2010, 11:02 AM   #25
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Check out the Astronomy Clubs in Germany, since they will need the same things as you do - a reasonably dark sky. They will know where the best sites are that are that are local.
09-06-2010, 06:16 PM   #26
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Thanks for the link; I shall look into it.
09-13-2010, 12:02 AM   #27
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You can turn off DFS in K20D using debug mode.
09-13-2010, 03:01 AM   #28
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QuoteOriginally posted by darky_mtp Quote
You can turn off DFS in K20D using debug mode.
:O

I so have to try that, first thing I'll do after lunch is to get to know how to get into the debug mode, I've only read something about creating a new textfile which allows you to do so; either way googles my friend. Thanks a lot for the hint.
09-13-2010, 05:07 AM   #29
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Enable debug mode with a modset file and add a SYSPARAM.TXT file with
[DISABLENR] 1@
inside.
DFS disabled !
When you can use interval shooter with this parameters :
30" exposures with 33" interval.
09-13-2010, 05:15 AM   #30
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Darky, is this something you've successfully done yourself?

I#m wondering if this approach is worth trying on K-7
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