This site is supported by the advertisements on it, please disable your AdBlocker so we can continue to provide you with the quality content you expect.

Long exposure NR

Discussion in 'X-Pro2 and X-Pro1' started by markopa, Apr 13, 2012.

  1. Arjay

    Arjay Admin Staff Member

    Joined:
    Feb 27, 2011
    Messages:
    12,774
    Likes Received:
    4,616
    Location:
    Munich, Germany

    -Return to Top-

    Could this mean that the long time NR threshold shutter speed is dependent on ISO values? Does anybody have indications for this assumption?
     
  2. jlaronge

    jlaronge Premium Member

    Joined:
    Mar 22, 2012
    Messages:
    456
    Likes Received:
    139

    -Return to Top-

    I suspect you're right on this assumption. I tested at ISO 200, 30sec. @f16 and ISO 6400, 2sec. @ f16 both of which allow the same amount of light to reach the sensor. At 6400 the LENR kicked in while at 200 it didn't. LENR didn't kick in at ISO 200 until 1min. 15sec.. I supposed you could go through each ISO @f16 and find the shutter speed at which it will kick in.
     
    f_random likes this.
  3. Arjay

    Arjay Admin Staff Member

    Joined:
    Feb 27, 2011
    Messages:
    12,774
    Likes Received:
    4,616
    Location:
    Munich, Germany

    -Return to Top-

    I just ran a test series with varying ISO values, all at f16, with the following results for fastest shutter times at which LENR is kicking in (all @ T, except for 200 ISO which was @ B ):

    ISO 200: 1min 10s
    ISO 400: 30s
    ISO 800: 15s
    ISO 1600: 8s
    ISO 3200: 4s
    ISO 6400: 2s
     
  4. flysurfer

    flysurfer Premium Member

    Joined:
    Aug 14, 2011
    Messages:
    3,239
    Likes Received:
    687
    Location:
    NUE

    -Return to Top-

    Makes perfect sense to me. 2^6 s = 64 seconds, which pretty much equals the 1 min 10 sec. at ISO 200.
     
  5. jlaronge

    jlaronge Premium Member

    Joined:
    Mar 22, 2012
    Messages:
    456
    Likes Received:
    139

    -Return to Top-

    This makes perfect sense. All are essentially the same exposure except for the ISO 200. Since ISO 200 is the native ISO for the sensor (and highest quality), that's probably why the extra exposure is allowed.

    Two questions:

    Does the dynamic range setting have any effect on this?

    Are the results better using a lower ISO without LENR?
     
  6. flysurfer

    flysurfer Premium Member

    Joined:
    Aug 14, 2011
    Messages:
    3,239
    Likes Received:
    687
    Location:
    NUE

    -Return to Top-

    Not as fas a I have seen.
     
  7. cbwerner

    cbwerner New Member

    Joined:
    Apr 10, 2012
    Messages:
    39
    Likes Received:
    2

    -Return to Top-

    I hear you, but it may be that you do not need to be concerned - let me try explaining.

    1. With a given sensor, the level of dark current noise noise is affected by 3 variables - ISO/gain, exposure duration, and the temperature of the sensor. Temperature is neither measurable or controllable with this camera so I'll set it aside (astro CCDs generally include a thermoelectric cooler that will cool to 35-40C less than ambient).

    2. Dark current at a given ISO will vary linearly by exposure duration, i.e., 2x exposure gives you 2x noise. I'm going to guess that at a given exposure, that ISO will also affect the level of dark noise linearly, but I'm assuming that ISO 6400 requires twice the current as 3200 and so forth.

    3. Dark current noise is one of four sources of noise in digital photography; readout/bias noise is actually the largest source of noise in digital sensors in most shooting situations.

    4. The type of scenes where we're getting into high ISOs and long durations are dim (yeah, duh :D ), or said another way, have a low signal to noise ratio. Thus the dark current noise becomes most problematic in shooting situations where not only is the dark noise at it's highest levels, but the signal in the scene is also at very low levels. So without reduction, the resulting image has a very poor S/N ratio, and therefore, sucks.

    I'm guessing based on what's reported in the thread that Fuji has made an engineering decision that dark current reduction does not have a noticeable impact on S/N ratios except where they have enabled it, and therefore it's not worth compromising the shooting in other scenarios. They might be wrong, or we might disagree with how they implemented it, but that would actually be an easy thing to test. I'd do it myself, but unfortunately, I can't yet count myself in the ranks of X-Pro 1 owners. Hopefully soon. :)
     
    f_random likes this.
  8. andymu

    andymu Member

    Joined:
    Apr 24, 2014
    Messages:
    88
    Likes Received:
    15
    Location:
    Glasgow UK

    -Return to Top-

    Since the 2nd image doesn't actuate the shutter, say you take a 5 minute exposure,
    Then when the camera is doing the 2nd 5 minute image, does the camera need to stay on a tripod for this?

    Reason I ask is, if it didn't need to stay on a tripod during the 2nd exposure I could swap a different camera on to the tripod while this happens and do other work
     

Share This Page