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Coloured spots on my dark images

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    gossyboy
    gossyboy  6460 forum posts United Kingdom
    24 Nov 2011 - 12:44 PM

    Hi, I have an Olympus E500. I have just had it professionally cleaned for the first time since I owned it about 5 years ago.
    The reason I took it was because I was getting loads of coloured spots on my images when doing darker long exposure type shots. The clean does seem to have reduced it but I just took a 6 second exposure in a dark room to check it and there are still quite a lot of different coloured dots of varying sizes.
    I'm pretty clueless when it comes to the workings of a camera. Are these dots being caused by dust? Or is there something else wrong with it.
    I could upload the image with the dots on if it helps anyone diagnose my problem?

    Cheers in advance.

    Paul Goss.

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    24 Nov 2011 - 12:44 PM

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    mikehit
    mikehit e2 Member 45758 forum postsmikehit vcard United Kingdom9 Constructive Critique Points
    24 Nov 2011 - 1:01 PM

    Yes, it wouldelp if you loaded up a sample image. But it sounds to me like 'colour noise' which is more apparent in dark areas of the image.

    Overread
    Overread  53745 forum posts England18 Constructive Critique Points
    24 Nov 2011 - 1:07 PM

    Yep that sounds like colour noise and is a product of long exposures. Try enabling the Long Exposure Noise Reduction mode in the camera. This mode works by taking a second photo after you take a shot, exposing the sensor for the same amount of time, but with the shutter closed so that no light gets through. It then deducts the colour noise from the second shot from the first to present a cleaner photo.

    sherlob
    sherlob e2 Member 82201 forum postssherlob vcard United Kingdom119 Constructive Critique Points
    24 Nov 2011 - 1:11 PM

    Hi Paul,

    This could be as simple as digital noise. What ISO are you using? An image would help - but consider doing this at 100% magnification if the dots are small. To minimise digital noise - you could try reducing the ISO to the lowest setting and trying to keep your camera cool. Noise is often caused as a consequence of the sensor becomming heated - sadly there is not a great deal that you can do about this during the actual exposure. You could also try using your in camera noise reduction mode (if it has one), although my experience is that this feature is more trouble than what it is worth.

    Adam

    gossyboy
    gossyboy  6460 forum posts United Kingdom
    24 Nov 2011 - 1:15 PM

    Thanks so far, some stuff I understand there and some I don't.
    I have just uploaded the black image but its not possible to see the dots in the state, they are more apparent if you enlarge it.

    gossyboy
    gossyboy  6460 forum posts United Kingdom
    24 Nov 2011 - 1:23 PM

    Just going to try zooming in on pic to enlarge the dots and will re upload

    gossyboy
    gossyboy  6460 forum posts United Kingdom
    24 Nov 2011 - 1:32 PM

    there's a crop of a quarter of the image on there now

    Gaucho
    Gaucho e2 Member 122047 forum postsGaucho vcard United Kingdom2 Constructive Critique Points
    24 Nov 2011 - 2:29 PM

    They look like hot pixels to me. Ignore them as pretty much every camera has them though some are worse than others. Do you see them if you aren't actually looking for them? If not don't worry about it.

    conrad
    conrad e2 Member 910870 forum postsconrad vcard 116 Constructive Critique Points
    24 Nov 2011 - 2:52 PM

    When doing long exposure after long exposure, I found that I could prevent this problem by switching the camera off now and then in between the shots.

    gossyboy
    gossyboy  6460 forum posts United Kingdom
    24 Nov 2011 - 2:58 PM

    I noticed it a lot when I took some late sunset / dark shots on hols in Turkey. When I opened up the image in photoshop and cropped it down a bit, the dots were everywhere. Took ages cloning them all out. I suppose it wasn't so noticeable when the image wasn't zoomed in but once you know they are there...... do you now what I mean?
    I was worried it was due to dust or something. If it's not and there's not a lot I can do about it, fair play.
    Off on a Caribbean cruise through Xmas and New Year and just wanted camera to be in best shape possible. Hoping to re light my photo fire and get some good shots. Not been on here for ages, just lost interest for a while.....

    Thanks for all your input!

    mikehit
    mikehit e2 Member 45758 forum postsmikehit vcard United Kingdom9 Constructive Critique Points
    24 Nov 2011 - 4:24 PM

    If it is noise you can slightly over-expose so that the noise in the dark areas is not as obvious when you re-correct the exposure. If you are doing things like sunsets then burning-out the highlights will be an issue and you can use a ND grad or exposure-bracketing to overcome it. Do you have an editing program with noise reduction on it?
    The sort of noise you mention is a problem with any camera so it is all about management.

    Last Modified By mikehit at 24 Nov 2011 - 4:25 PM
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