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X-T1 - LOTS of hot pixels, or something else?

Discussion in 'X-T2, X-T1, X-T20, X-T10' started by cyclopath, Mar 16, 2017.

  1. cyclopath

    cyclopath Member

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    Hi everyone,

    I am getting into some long exposure photography for the first time. Last night was my first go at it and I was pretty pleased with the results. However, when I got home to edit the shots, I noticed that most of my files were riddled with noise/hot pixels! The one attached was the worst one, but there were several others like it. It seems that the longer the shutter speed, the worse it was.

    3 year old Fujifilm X-T1
    XF23mm F1.4 shot at f/8
    ISO 400
    SS 250sec
    10 stop HOYA Pro ND Filter
    HOYA Pro CPL Filter


    Can anyone shed any light on this?
     
  2. 5280Pics

    5280Pics Well-Known Member

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    With a 4min exposure, that is probably almost all long exposure/thermal noise, mixed with some hot pixels.
     
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  3. X-Mount

    X-Mount Martin

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    I have also found this with the xt2 in the shadows of images' 250 second shutter is a bit too long' the same effect in these images can be achieved by using a 6 stop ND like a little stopper or equivalent with a vastly faster shutter speed but still slow enough to blur.
    Also the more underexposed the image trying to edit it in post can push the file too far.

    I've found that if I expose correctly at the time of shooting there are less underexposed areas to pull back in pp and I don't have push the file too far .
     
  4. visorvet

    visorvet Premium Member

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    There is also an on/off setting called Long Exposure Noise Reduction or something similar - perhaps check that it is turned on? I don't do exposures this long so am not sure of this setting's practical limits.
     
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  5. CIA

    CIA Member

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    doing these long exposures will fry your sensor sooner that expected
     
  6. ToneXA1

    ToneXA1 Well-Known Member

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  7. X-Mount

    X-Mount Martin

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    Although this is probably a better setting for the camera' in real world condtions its a pain to use. A 250 second exposure would take another 250 seconds to create the image with LENR turned on .

    Whilst this is happening the camera is unusable .

    The image below which is a quick crop of an image i took a couple of days ago' which on right hand side has the same issues.

    Screen Shot 2017-03-16 at 06.52.22.png
     
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  8. cyclopath

    cyclopath Member

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    Thanks for that. Super helpful link. Pretty sure I took several exposures quickly in a row so assuming at this point that the sensor was just running quite hot. It was also a balmy night here. First time out with the ND filters though so it's all a learning curve!
     
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  9. Mr Perceptive

    Mr Perceptive Premium Member

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    I have shot a lot of long exposures with X-E2, X-T1 and now X-T2, I have never had hot spots, even shooting exposures as longs as 15 minutes, nor have I seen the type of noise that you are exhibiting here, I think the key here is what does the histogram look like?? If it is all squashed to the left hand side then maybe you are seeing the equivalent to luminance noise that you get shooting at higher ISO, a 4 minute exposure at such low light levels might give this effect (first poster). I try to aim for a normally distributed histogram, ETTR but not clipping.

    10.5 minutes
    [​IMG]
    170204 Llyn Ogwen and Tryfan
    by David Yeoman, on Flickr

    Just over 5 mins
    [​IMG]
    170129 West Kirby Marina 1
    by David Yeoman, on Flickr

    Both shot on X-T2 with LENR turned off
     
    Last edited: Mar 16, 2017
  10. lawsofphysics

    lawsofphysics Premium Member

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    I think Mr Perceptive's excellent advice is important.

    Don't just think about the noise. Think about the signal level too.

    When artifact (thermal noise) signal levels are below the quantum (shot) noise and read noise levels, they are usually below the signal-detection threshold of the analog-to-digital converter. If they are not digitized they won't be in your image. One way to keep the thermal noise levels below the ADC threshold is to increase the signal (light) level.

    The problem isn't the noise level is too high. The problem is the signal level is too low. The solution is to increase exposure. More exposure means more signal.
     
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  11. apsphoto

    apsphoto Premium Member

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    Those look like dark noise subtraction issues. I never use the LENR much like David in the post above I have not had any issues with hot and cold pixels. If you had LENR turned on and you get those stuck pixels like that it is generally called cold pixels, hot pixels are usually colored, red, green etc. Cold pixels are usually caused by an incorrect dark frame subtraction.

    Alan
     
  12. Mr Perceptive

    Mr Perceptive Premium Member

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    This ^^ - Get the histogram right without the filter, then add the filter and do the required calculation. I always take a reference shot without the filters, as this a) gives me the target histogram and b) gives me the colours of the original image, so I can correct any filter colour cast if required (with good filters ie Hitech Firecrest, you get little or no colour cast).

    If I've done everything right, my two histograms usually are a good match.
     
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  13. cyclopath

    cyclopath Member

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    Thanks you for that explanation. I had never even heard of that before, great information for someone just getting into long expo.

    This is a great idea. I will definitely give your method a shot next time I'm out. Thanks for your earlier post as well, the histogram was definitely exposed to the left. I think I underexposed a touch by habit, as normally with my street shots the Fuji's have such great shadow recovery. But I can see why in this case it's not the best idea.
     
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