D80 question (new member!)

Discussion in 'Digital Discussion & Q&A' started by nrois02, Feb 12, 2009.

  1. nrois02

    nrois02 TPF Noob!

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    hello to everyone that reads this. I am a new member here so..... just want to say hi and ask a question.

    why does my nikon d80 give me these purple corners when i do long exposures at night and there is cloudy parts in it why is that?. it was a 25 minute exposure btw.
    [​IMG]

    and then photoshopped a little bit
    [​IMG]
     
  2. NM Rich

    NM Rich TPF Noob!

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    Are there city lights over in the direction where the purple appears? Maybe the camera sensor is picking up some kind of stray light that the naked eye can't detect...
     
  3. kundalini

    kundalini Been spending a lot of time on here!

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    I can't see the photos while logged into work computer, but it sounds like Chromatic Abberation (CA, purple fringing). Some lenses are more problematic than others. Look at photozone.de for your lens to see if it is susceptible.
     
  4. epp_b

    epp_b No longer a newbie, moving up!

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    It's amp noise. Amp noise occurs from the sensor heating up during long exposures. The D80 is known for this.
     
  5. Joves

    Joves No longer a newbie, moving up!

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    Exactly! It is amp noise on that corner. The cloudiness may also be a part of that or it is picking up any light pollution as well. When I did astrophotograpy my CCD camera was cooled with nitrogen.
     
  6. epp_b

    epp_b No longer a newbie, moving up!

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    It's doubtful that it will be that high in the sky. On a clear night, you'll see it close to the horizon (notice the gradient from light to dark from the horizon upward).

    I don't know how cold it gets in Boston, but I imagine it might work better if it's -20C outside like it is here :lol:
     
  7. nrois02

    nrois02 TPF Noob!

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    how can i get it to stop happening? is there alternate ways to get it to stop?
     
  8. Garbz

    Garbz No longer a newbie, moving up!

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    It's your camera's way of saying "For the love of god stop the exposure before you cook my sensor completely!" Not quite that extreme but there have been cases of Digital SLRs which have completely destroyed sensors thanks to owners attempting hour long startrail shots. Proper sensors for taking long exposures like this look like little webcams bolted on HUGE heatsinks and peltier units to keep them cool.

    The sneaky workaround with digital SLRs is to take repeated images, 20seconds on 10seconds off. The amps will reset between each exposure so you get close to no noise, and the off time for the sensor prevents the camera from being turned into a geeky paperweight.

    I used this program Image Stacker to stack this shot:
    [​IMG]

    The total star time for this is about 2 hours. The only downside being that if you zoom in at 100% you can see that the stars do not form a continuous line. But it was taken on a D200 no less which has a considerably worse purple bleeding problem than the D80.
    Serious check out this 20 minute shot:
    [​IMG]
     
  9. blash

    blash TPF Noob!

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    I actually kind of like that red shot, nice and abstract and warm and fuzzy at the same time, like a nice long exposure on film with plastic optics :p

    Or, you could just use film. $20 for crappy used manual camera + $5 for film + $5 processing = instawin astrophotography.
     
  10. epp_b

    epp_b No longer a newbie, moving up!

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    or not
     
  11. nrois02

    nrois02 TPF Noob!

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    this seems like a good way but theres nothing that they sell "aftermarket" to help out with doing this? cause i dont want to sit there for 3 hours and have to take 500 pictures will im doing it you know?
     

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