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01-13-2012, 03:47 AM   #1
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Stuck Pixel Hell!?

I couldn't find a help box so I guess this will do.

Straight to the issue; a couple of days ago I started to notice these little red, green, and blue dots turn up on some of my photos after doing a long exposure star trail for 1 hour (which turned out over exposed anyway).

Since then I have done about 4 other long exposure star trails however they only went for 30 minutes each. You can see them here: Flickr: Robs L's Photostream

I use Light room 3, which maps out the pixels before you view it (but because my computer is slow I can see it happen).

I use a K200D which has served me long and hard, and has done over 10000+ exposures.

In one particular photo there were a million of them (i've attached a screen shot), however in most of them there were about 5 or six, all in the same spots but fairly spread out.

I really hope I haven't damaged the cameras sensor :S because I have a photo shoot coming up and I would really like some useable photos out of it.

Should I give my camera a break? I use it nearly every day.

Anyway, I would love some feedback as to what others think it could be (just take a peek at the attachment )

Thanks so much Pentax Forum Community!

The picture below is zoomed in as it would show the dots on the original one: ... they are literally everywhere in this one.

Name:  Screen shot 2012-01-13 at 9.51.01 PM.png
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Last edited by Robtography; 01-13-2012 at 04:01 AM. Reason: adding stuff
01-13-2012, 04:07 AM - 1 Like   #2
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Esh, it looks to me like your sensor is giving up... I've seen this on small point-and-shoot cameras, never on a DSLR before!

One suggestion would be to try the 'dust removal' feature (does the K200D have this?) - maybe this will shake some life back into it! ;-)

I hope it holds out for your shoot.
01-13-2012, 04:16 AM   #3
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Oh no! :S It is a fairly scary thought to think that I could have a dead camera! Unfortunately it technically isn't mine either.

I just find it odd how this image had heaps and other only have a few... But owell

Thank you for the reply @Stuart Windram
01-13-2012, 06:03 AM   #4
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I don't know that this is unusual for such a long exposure. I suggest you look into an interval timer for taking a series of shorter exposures, then using dark frame subtraction to deal with noise. I've never done such long exposures myself but I gather these techniques are the norm for astrophotography these days.

01-13-2012, 06:53 AM   #5
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Your camerA is okay. Stuck pixels aka "hot pixels" are normal during a very long exposure. The sensor heats up during the exposure and that increases the appearance of noise.

You can get rid of hot pixels by taking an equally long exposure with the lens cap on and subtract the hot pixels. This process is called dark frame subtractiom.

The other poster who mentioned stacking shorter exposures is on the right track. Instead of an hour exposure, you could try 120 30-second exposures. Stack them using software. Look up Deep Sky Stacker and Startrails for software that can get you started. It's more complex than doing one very long exposure but can give fantastic noisefree results.
01-14-2012, 07:09 PM   #6
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There's really nothing wrong with the camera. My old *ist DS created even noisier photos just after 30 seconds exposure. For 30 minutes exposures I would suggest a film camera. Film doesn't heat up or anything.
01-16-2012, 05:05 PM   #7
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Thanks for the info everyone! I will definitely look into the dark frame method.

The problem I would have using the image stacking process is that it takes the camera the practically the same amount of time that the image was take for to process the image. so If I were to take a 30 second exposure it would take around 25 seconds to process it, (I shoot RAW) meaning that I would have lots of little gaps in the photos. If there is any way to get around this I would love to know though I did think of tethered shooting but K200D has been left out with that feature. Maybe shooting in RAW is what is holding me back?

Here is one I took last night for about 5-10 minutes I think, and it has just as many as the one i took for 30 minutes.

Thanks all once again for the replies! reassuring me my camera still has some oomph left in it

Name:  Screen shot 2012-01-16 at 11.54.18 PM.jpg
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01-16-2012, 05:28 PM   #8
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QuoteOriginally posted by Robtography Quote
The problem I would have using the image stacking process is that it takes the camera the practically the same amount of time that the image was take for to process the image. so If I were to take a 30 second exposure it would take around 25 seconds to process it, (I shoot RAW) meaning that I would have lots of little gaps in the photos. If there is any way to get around this
Turn off noise reduction; that is the bulk of the processing time. The in-camera NR is in fact dark frame subtraction, which is why it takes about as long as the exposure.

01-16-2012, 05:44 PM   #9
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QuoteOriginally posted by baro-nite Quote
Turn off noise reduction; that is the bulk of the processing time. The in-camera NR is in fact dark frame subtraction, which is why it takes about as long as the exposure.
awesome I will try this tonight if the skies are on my side. Thanks a lot

you can check out my star trail shots right here: Star Trails - a set on Flickr

Edit: I just look on my camera to see where to turn Noise Reduction off but I can't find it :/ anyone?
01-16-2012, 05:52 PM   #10
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On my camera (K10D), it is under the Custom Setting menu, 3rd page.
01-16-2012, 06:02 PM   #11
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QuoteOriginally posted by baro-nite Quote
On my camera (K10D), it is under the Custom Setting menu, 3rd page.
Ahh yes I see. Thanks a lot for the help much appreciated
01-16-2012, 08:09 PM   #12
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QuoteOriginally posted by Robtography Quote
awesome I will try this tonight if the skies are on my side. Thanks a lot

you can check out my star trail shots right here: Star Trails - a set on Flickr

Edit: I just look on my camera to see where to turn Noise Reduction off but I can't find it :/ anyone?
You still want to use a dark frame, just do a single one at the end of your series.

If you are using Photoshop, add the dark frame on top with the layer mode set to difference. That will clear the hot pixels and leave every thing else.
01-18-2012, 10:46 PM   #13
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So I tried this separate frames method the other night. It kind of failed. Can anyone suggest some setting the camera should be on? also, when I merged the images I used an image layer thing, which didn't really work very well. So yeah, any help would be appreciated! love the pentax forum community!
01-18-2012, 10:54 PM   #14
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QuoteOriginally posted by Robtography Quote
So I tried this separate frames method the other night. It kind of failed. Can anyone suggest some setting the camera should be on? also, when I merged the images I used an image layer thing, which didn't really work very well. So yeah, any help would be appreciated! love the pentax forum community!
The dark frame is taken with the exact same settings as the rest of the pictures in the sequence, except with the lens cap on.

Post an example of how it turned out, and what steps you took (and what software you are using) so we can troubleshoot.
01-19-2012, 12:36 AM   #15
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QuoteOriginally posted by alohadave Quote
Post an example
Sure thing. I took 2 different test sequences. The first one I set the camera to ISO 200 f./11 at 28mm and did 30, 30 second captures with NR off (as suggested). It worked seamlessly by the way . The second one I shot with the same settings but only 15, 30 second exposures . I used Registax (not sure if thats the right thing to use) and I have posted the results below. I didn't really get the dark frame business so I used the dark frame generator in the program. I also didnt set any alignment points because I didnt think i needed any because of the tripod etc.

Shot 1

Name:  IMGP3361.jpg
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Shot 2

Name:  IMGP3391.jpg
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Size:  12.0 KB
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