Loading ...
Sorry, an error occurred while loading the content.

Re: [ccd-newastro] Dark Library info...

Expand Messages
  • Ron Brant
    No, the cooler on the camera just doesn t have to work as hard to get to -20 degrees. Ron ... From: Dave To: ccd-newastro@yahoogroups.com Sent: Sunday,
    Message 1 of 6 , Dec 9, 2012
    • 0 Attachment
      No, the cooler on the camera just doesn't have to work as hard to get to -20 degrees.
      Ron
      ----- Original Message -----
      From: Dave
      To: ccd-newastro@yahoogroups.com
      Sent: Sunday, December 09, 2012 8:25 AM
      Subject: [ccd-newastro] Dark Library info...



      I had a lot of good info on the darks question I posed earlier but I forgot to ask...If I want to make a dark library..If my camera is set to -20 Celcius...in order to be usefull as a dark on other substhe Ambient temperature should be the same too to be able to use on another sub,correct? Say Camera -20 degrees and ambient -10 degrees for a total of -30 degrees.If it was 0 degrees ambient...I wouldn't be able to use the dark on any other ambient temp.Correct???Thanks and Clear skies...Dave





      [Non-text portions of this message have been removed]
    • randy_nulman
      Hi, Ambient temperature is not relative to your discussion below. You need to consider the camera/ccd net temp. For example, if you decide that you will
      Message 2 of 6 , Dec 9, 2012
      • 0 Attachment
        Hi,
        Ambient temperature is not relative to your discussion below. You need to consider the camera/ccd net temp. For example, if you decide that you will never image below -20C, then simply take your dark library at that temp (-20C is usually fine for imaging depending on the camera and read noise).

        You can always "scale" darks in most programs...CCDStack is very good at this. Therefore, if I were you I would develop a dark library at your lowest "stable" temp and use a time frame longer than your "lights" would be.

        Then, using the software...you will need a good bias master combined from a reasonable amount of data to combine to create a master...necessary if you scale, and use this in the program of your choice. Therefore, if for example you take 20 or 30 minute subs of darks to combine into your library, you can (with the master bias) always apply this quite well to shorter "light" frames...better to scale down then to scale up in terms of exposure times.

        The ccd temp should be consistent between the light and dark frames even when scaling, but the exposure time of your lights can be less.

        It's easy to use non-imaging time to create the master dark and bias data. Ambient temps only apply in terms of how cool you can make the camera, so be safe and use a reasonable number (and many subs to combine) that do not exceed your ability to match the light frame temps. Remember that the more subs you use for both the dark library and the "master bias", the less the noise contribution will be.

        Sorry for the long answer, but I hope this answers your questions?

        Hope this helps,
        Randy

        Randy Nulman
        http://nulman.darkhorizons.org


        --- In ccd-newastro@yahoogroups.com, "Dave" <terrarouge@...> wrote:
        >
        > I had a lot of good info on the darks question I posed earlier but I forgot to ask...If I want to make a dark library..If my camera is set to -20 Celcius...in order to be usefull as a dark on other substhe Ambient temperature should be the same too to be able to use on another sub,correct? Say Camera -20 degrees and ambient -10 degrees for a total of -30 degrees.If it was 0 degrees ambient...I wouldn't be able to use the dark on any other ambient temp.Correct???Thanks and Clear skies...Dave
        >
      • Mike Dodd
        ... Not quite sure what you re asking with the Camera -20 degrees and ambient -10 degrees for a total of -30 degrees bit, but generally speaking, dark frames
        Message 3 of 6 , Dec 9, 2012
        • 0 Attachment
          Dave wrote:
          > I had a lot of good info on the darks question I posed earlier but I
          > forgot to ask...If I want to make a dark library..If my camera is set
          > to -20 Celcius...in order to be usefull as a dark on other substhe
          > Ambient temperature should be the same too to be able to use on
          > another sub,correct? Say Camera -20 degrees and ambient -10 degrees
          > for a total of -30 degrees.If it was 0 degrees ambient...I wouldn't
          > be able to use the dark on any other ambient temp.Correct???Thanks

          Not quite sure what you're asking with the "Camera -20 degrees and
          ambient -10 degrees for a total of -30 degrees" bit, but generally
          speaking, dark frames should be at the same temperature as the light
          frames they're applied to.

          For example, if you take light frames with the camera cooled to -20C,
          you should subtract darks made with the camera cooled to the same -20C.

          I recall discussions about scaling darks at different temperatures, but
          I don't know how, and I think that it is not a good idea.

          I always make darks immediately after an imaging session while the
          camera is still cooled, and apply them _only_ to the light frames from
          that session.

          I gave up on a dark library long ago after I began cooling the camera to
          almost the maximum it could achieve on a given night (i.e., cool to
          maximum, then raise the set point until the cooler operates arount 80%).
          If a session's camera temperature was, say, -18C, a library dark at -15C
          or -20C would be sub-optimal.

          As I understand it, even a couple degrees lower chip temperature reduces
          noise by a non-trivial amount. I figure it's good to get this
          improvement and _not_ lose anything -- even a small amount -- by
          applying a mismatched-temperature dark.
          --
          Mike

          Mike Dodd
          http://astronomy.mdodd.com
          Louisa County, Virginia USA N37.58.23 W77.56.24
        • geoff
          I think you misunderstand what the set point on the camera means. If I understand you correctly you seem to think that a set point of -20 means that the camera
          Message 4 of 6 , Dec 10, 2012
          • 0 Attachment
            I think you misunderstand what the set point on the camera means. If I understand you correctly you seem to think that a set point of -20 means that the camera cools -20 below ambient. This is not what happens; a set point of -20 means that the camera chip will be at -20 whatever the ambient temp may be.
            Geoff

            --- In ccd-newastro@yahoogroups.com, "Dave" <terrarouge@...> wrote:
            >
            > I had a lot of good info on the darks question I posed earlier but I forgot to ask...If I want to make a dark library..If my camera is set to -20 Celcius...in order to be usefull as a dark on other substhe Ambient temperature should be the same too to be able to use on another sub,correct? Say Camera -20 degrees and ambient -10 degrees for a total of -30 degrees.If it was 0 degrees ambient...I wouldn't be able to use the dark on any other ambient temp.Correct???Thanks and Clear skies...Dave
            >
          • mark_manner_spot_obsrv
            Actually, if you set -20C in your camera control system, it mean -20C, period, that is, 20 degrees below 0 degrees centigrade, not -20 from the current ambient
            Message 5 of 6 , Dec 10, 2012
            • 0 Attachment
              Actually, if you set -20C in your camera control system, it mean -20C, period, that is, 20 degrees below 0 degrees centigrade, not -20 from the current ambient air temperature. What you do is to pick a temperature that your camera can reach, and stick with it. Depending on where you image and how good your camera can cool, perhaps in summer you can use -10C for all your darks and subexposures, and in winter -20C. The cooling delta that you see advertised with cameras is a delta from the current air temperature. So, for example, an SBIG STL camera can cool about 35 degrees below the air temperature on a given night.


              --- In ccd-newastro@yahoogroups.com, "geoff" <ghsmith45@...> wrote:
              >
              > I think you misunderstand what the set point on the camera means. If I understand you correctly you seem to think that a set point of -20 means that the camera cools -20 below ambient. This is not what happens; a set point of -20 means that the camera chip will be at -20 whatever the ambient temp may be.
              > Geoff
              >
              > --- In ccd-newastro@yahoogroups.com, "Dave" <terrarouge@> wrote:
              > >
              > > I had a lot of good info on the darks question I posed earlier but I forgot to ask...If I want to make a dark library..If my camera is set to -20 Celcius...in order to be usefull as a dark on other substhe Ambient temperature should be the same too to be able to use on another sub,correct? Say Camera -20 degrees and ambient -10 degrees for a total of -30 degrees.If it was 0 degrees ambient...I wouldn't be able to use the dark on any other ambient temp.Correct???Thanks and Clear skies...Dave
              > >
              >
            Your message has been successfully submitted and would be delivered to recipients shortly.