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NEX-6 and noise

Discussion in 'Image Processing' started by TonyTurley, Jul 14, 2014.

  1. TonyTurley

    TonyTurley TalkEmount Hall of Famer

    Apr 24, 2013
    West Virginia, USA
    I decided to attempt some astrophotography around our rented cabin while on vacation, and was surprised to find the noise from the NEX-6 captures - at ISO 800 - appeared to be worse than it ever was on my 5R, even at 3200. The only thing I can think of is sensor noise due to having the shutter open too long (20s and 30s), but don't the 5R and 6 use the same sensors? I use RawTherapee and GIMP on a Linux box, and I haven't found a work flow sufficient to handle noise yet. I just don't care for the results I'm getting. It's almost enough to get me to install W8 just to get LR or Topaz Denoise. Anyone using RT & GIMP have a good work flow for reducing noise? Attached is an example.

    Tony

    PS: I know I need to reduce my shutter time; if you zoom into the photo, the stars are tiny trails rather than points.
     

    Attached Files:

    • Like Like x 3
  2. stephen431

    stephen431 TalkEmount Regular

    112
    May 2, 2014
    That color noise is due to under exposure. At ISO 800, a 30 second exposure is pretty short for astro. It also looks like something was lighting your foreground from the direction of the camera

    Shooting astro with close foreground elements usually requires stacking multiple photos to expose the foreground separately and masking. I'm not really familiar with Gimp though. You could always convert the sky to monochrome.
     
  3. Electric Shepherd

    Electric Shepherd TalkEmount Regular

    103
    May 12, 2012
    Leicestershire, U.K.
    Ben
    Stupid question, but you did have the long exposure noise reduction switched on? All sensors get hot with prolonged exposures which increases noise, taking a dark frame with the same exposure helps the camera to cancel out sensor based noise
     
  4. alaios

    alaios TalkEmount All-Pro

    Jan 11, 2013
    Düsseldorf
    Alex
    Hi, the problem here is from the raw therapee... I had similar problems also with raw files in linux... most of the time does not understand fully the format.
    Check on a windows machine and post back
    A
     
  5. José De Bardi

    José De Bardi Assistant in Virtue

    Aug 31, 2013
    Dorset, UK
    José
    Conversely, I recommend disabling all NR, options (there are 3 or 4 from memory relating to High ISO/Long Exposure), also disable DRO. My results were MUCH better once I did this.
     
  6. Electric Shepherd

    Electric Shepherd TalkEmount Regular

    103
    May 12, 2012
    Leicestershire, U.K.
    Ben
    I agree about DRO [pointless if shooting Raw like I do] and high ISO NR, but long exposure NR with dark frame noise extraction is pretty much a must for long exposure work.
     
  7. alaios

    alaios TalkEmount All-Pro

    Jan 11, 2013
    Düsseldorf
    Alex
    I guess that DRO even if is enabled will not affect the RAW files...
    why do you disable high iso NR?
     
  8. TonyTurley

    TonyTurley TalkEmount Hall of Famer

    Apr 24, 2013
    West Virginia, USA
    My bad - I forgot to check the NR settings on my new NEX-6 before trying astro shots. Long Exposure NR was "On", High ISO NR was "Normal", and DRO was "Auto". They are now "Off", "Low", and "Off", same as the 5R. I should now be able to go to ISO 3200 and shorter times, as I've done with the 5R. Thanks for the reminders. I am a bit chagrined at myself for my inattention to detail, ruining my vacation night shots.

    The foreground lighting was indeed from a cabin across the road and behind me. That was intentional.

    Tony
     
  9. stephen431

    stephen431 TalkEmount Regular

    112
    May 2, 2014
    Try keeping Long Exposure NR on, unless you're taking fast sequential long exposures and can't wait for the camera to expose the black frame.
    If you're taking several long exposures you're going to end up with a bunch of hot pixels that noise reduction software thinks is exposed. I didn't have much time playing with the NEX-6, but the a6000 sensor heats up pretty quickly.

    High ISO NR should be on the lowest setting if you're shooting long exposure on a tripod.
    DRO should definitely be off. I'm totally speculating about what DRO is doing, because it is proprietary Sony tech, but I have a suspicion (based on some of the results I've gotten) that DRO is applying selective ISO levels to different parts of the sensor during exposure.

    If you're trying to get the stars to expose and also expose the foreground, try taking 2 exposures. One to expose the sky, and one to expose the foreground. That also lets you get your foreground in focus and the stars in focus without stopping down. I'm not familiar with GIMP, but I'm guessing it can probably do layer masks. In a shot like that one, it would be easier to mask in the sky exposure over the foreground exposure.
    If you still have trouble with color noise in the sky, you can copy another sky layer to black&white and blend that into the color sky layer.

    I believe you can also run Registax under Linux (best if you're trying to get a sharp moon in the background), if you want to play around with that.
     
    • Like Like x 1
  10. TonyTurley

    TonyTurley TalkEmount Hall of Famer

    Apr 24, 2013
    West Virginia, USA
    GIMP does indeed do layer masks. I'm not a guru at it, but I've used it to blend layers with 2 different exposures for foreground and background. It is a bit fiddly, but works.

    Tony
     
  11. dannat

    dannat TalkEmount Regular

    86
    Jun 22, 2014
    VIC
    it does look quite noisy -I dont think the tone of the lights from the cabin have helped -I have got decent results with long exp. noise reduction ON, high iso LOW
    for curiosity, what kind of temps did you expose in -and where was the camera before you took it out
    I use DxO -which for me ives excellent results - I tried gimp for quite a while but never got great results out of it
    what was your WB setting?
     
  12. WestOkid

    WestOkid TalkEmount All-Pro

    Jan 25, 2014
    New Jersey, USA
    Gary
    Sounds like you plan to turn of long exposure NR. I don't think that will help you. It really is necessary as you will certainly get hot pixels in your raw file without it. You will have to manually remove them because noise reduction programs will not detect them. Good luck
     
  13. chrid

    chrid Super Noob

    807
    May 5, 2014
    australia
    Chris
    I also struggle with noise on my nex-6 but mainly from not being good with light rooms noise reduction, this is at iso 400
    15061204669_561d290e61_b. _DSC6601 by Chris Thackray, on Flickr
     
    • Like Like x 2
  14. TonyTurley

    TonyTurley TalkEmount Hall of Famer

    Apr 24, 2013
    West Virginia, USA
    Thanks for the replies. I heven't been out to try different settings since starting this thread. Your photo looks fine to me, Chris.

    Tony
     
  15. chrid

    chrid Super Noob

    807
    May 5, 2014
    australia
    Chris
    Ah but it could be better :rolleyes: