Camera Noise (Long Exp)

Discussion in 'Photography Beginners' Forum' started by Nekoism, Jan 8, 2007.

  1. Nekoism

    Nekoism TPF Noob!

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    Hi, I am hoping someone here can explain this problem I am having and maybe help me solve it.

    I took some long exposure photos of a theater for my company's use and noticed that the images produced some very noticeable noise, almost like dust but with blue CA around it. The noise can't be missed at 100%.

    The camera I used:

    Nikon D2Xs with AFS-Nikkor 18-70mm f/3.5-4.5 DX G ED-IF Lens. The lens is from D70s kit lens. I used this lens because the lens that was purchased with the D2X is not very good (well not a wide enough angle 24-120mm).

    I shot the photos at f/8 at 100iso 2min exposure (bulb). RAW+Fine JPEG file.

    I also used a Coolpix 8700 with the wide angle adapter and in the same theater setup the noise was still present but not as noticeable as the d2x.

    I have a feeling it might be dust in the sensor. Maybe the dust got in there when I put the lens on. Could it be that the lens is not capable? I should also note that my kit lens had a UV filter on at the time. I can deal with this in photoshop but the noise is spread throughout the whole image it'll take me a while to clean it up.

    I should also note that I took some long exp images of the projectors in the projection room and those did not produce *any* noise.

    If anyone knows of a free image hosting service that is quick and easy I can post the images.

    Thanks!
     
  2. Alex_B

    Alex_B No longer a newbie, moving up!

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    what aperture did you use? with ver small apertures (22 and beyond) dust on the sensor can become very visible indeed.

    another possibility is that it is hot pixels, which every camera has in long exposures. they can be eliminated in post processing. some brands also allow to map them out electronically. and some, like my canon, allow them to be eliminated while shooting with a second long exposure with closed shutter.
     
  3. Nekoism

    Nekoism TPF Noob!

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    f/3.5 is the max aperture.

    Everytime I think I understand certain parts of photography, I realize that I don't. It boggles my mind. I had no idea about the hot pixels in long exp.

    Could it also be that there is dust in between the UV filter and lens? I guess you'll only know if you see the pictures.
     
  4. Alex_B

    Alex_B No longer a newbie, moving up!

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    OK, that is the max aperture of your lens, but at what aperture was the lens when shooting?

    [EDIT:] sorry, i should read more carefully, just saw you stated f/8 !!! SORRY!

    there is always a lot to learn for all of us :)

    I doubt it unless you can see it on the glass with your eyes.
    dust on glass is harmless compared to dust on the sensor. normally you would not get a sharp image of dust on your front lens.

    and you are right, posting an example might help people in here to guess what it could be ;)
     
  5. Alex_B

    Alex_B No longer a newbie, moving up!

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    at f/8 I would not think it is any sort of dust unless it is giant dust bunnies....
     
  6. D-50

    D-50 TPF Noob!

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    If you use a 2 minute exposure you are going to get a decent amount of noise, try reshooting in a higher ISO. Two minutes seems really long for a night exposire of a building, are there no lights around it at all.
     
  7. Alex_B

    Alex_B No longer a newbie, moving up!

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    well, i did 10 minutes and more exposures in a well lit room recently, that caused not a hell lot of more noise.
     
  8. Nekoism

    Nekoism TPF Noob!

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    Here's a 100% crop of the affected area:

    [​IMG]

    Here another area:

    [​IMG]

    If needed I can provide the original file (JPEG) if anyone is interested.
     
  9. Alex_B

    Alex_B No longer a newbie, moving up!

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    i can see some noise in the image, but what you are referring to, to me looks very much like hot pixels.
     
  10. Nekoism

    Nekoism TPF Noob!

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    Ahhh okay so it is hot pixels. In the images I posted those floating blue-white noise is what I am referring to.

    Is there any way to prevent them from appearing in future photographs? Is there any in camera settings or post-processing technique I can use?
     
  11. Alex_B

    Alex_B No longer a newbie, moving up!

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    since I am a Canon person, I don't know such details regarding Nikon .. hmm, some Nikonian please answer ;):)

    in post processing there must be some software tools, or some raw converters wich can handle it. since i can do it in camera, I would not know wwich though :(
     
  12. Sw1tchFX

    Sw1tchFX TPF Noob!

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    That's weird that you get those, i don't get that on my D70s. When you do exposures longer than 30 seconds, turn Long Exposure Noise reduction ON. I use it on my D70 for 30+ second long exposures to get rid of a purple haze in the top left. It should work for your hot pixels too.
     

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