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RE: RE: Dark frame integration times

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  • stan_ccd
    QE is independent of temperature but of course dark noise decreases with decreasing temp so it can be advantageous to run cold, esp for narrow band (the sky
    Message 1 of 22 , Sep 28, 2013
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      QE is independent of temperature but of course dark noise decreases with decreasing temp so it can be advantageous to run cold, esp for narrow band (the sky noise from normal imaging usually drowns out dark noise).

       

      The problem with going as low as you can go is that the actual CCD temp becomes overly affected by ambient temp and is unstable.  If temp varies during an exposure then the result is un-reproducible and results in a poor dark subtraction fit.  Always leave some headroom (e.g. do not exceed 80% TEC power).

       

      Stan



      ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

      Related question: What temperature should you set your camera to? As low as it will go? 

      Does quantum efficiency drop off as temperature decreases?


      Thanks.


      Larry Leitch

       



      ---In ccd-newastro@yahoogroups.com, <s24man@...> wrote:

      Ron,


      You're right, I meant "darks" not "flats", and no doubt there are better statistical methods to use.  I'm not someone who just likes to push buttons and watch things go without understanding really what I'm doing.  


      CCD stack has three ways to combine dark images.  A simple mean, a min-max clip and sigma reject mean.  The first two I understand, and the third I don't--yet.  (And I believe Pixinsight has a few more options).   I'm slowly dissecting Adam's videos because he's very good at explaining what he does--but he hasn't the time to go over absolutely everything.  


      Stu






      ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

      The bottom line is that there are probably better statistical methods for lowering the total noise in darks. (I presume you meant darks...)

      Ron Wodaski



      On Sep 26, 2013, at 9:47 AM, Stuart Forman <s24man@...> wrote:

       

      Thank you guys,  That's what I've been doing.  I've just been taking a lot of flats (a library of 40 or so) with the same integration time of the lights.  I just wanted to know if anybody was doing it the way Adam was talking about, and if there was an advantage to it. 
       
      Regards
      Stuart


    • Ron Wodaski
      Colder temps are always beneficial, but only so long as the camera s cooler can maintain that temperature in a stable way. If your camera is using 95% of it s
      Message 2 of 22 , Sep 28, 2013
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        Colder temps are always beneficial, but only so long as the camera's cooler can maintain that temperature in a stable way. If your camera is using 95% of it's cooling capacity, it doesn't have enough headroom to keep the temperature stable. For most amateur cameras, 80% of capacity is a reasonable max - and I usually like to be at 70% for really long exposures, but that's pretty conservative.

        Professional cameras and high-end amateur cameras tend to always keep extra capacity in reserve; they don't even let you approach 100% of capacity. 

        As Stan noted, QE is QE; it's not affected by temperature. 

        What lower temperature buys you, mostly, is lower noise, mostly in the form of lower dark current. Professional cameras are run at extremely low temps for this reason. Our Princeton Instruments Pixis camera has less than one electron per hour of dark current, for example. If the camera is also designed either with a very large full well or very low read noise, then you also get much better dynamic range, which allows you to use shorter (sometimes much shorter) exposures, which improve efficiency.

        Ron Wodaski



        On Sep 28, 2013, at 4:24 AM, k3fit@... wrote:

         

        Related question: What temperature should you set your camera to? As low as it will go? 

        Does quantum efficiency drop off as temperature decreases?


        Thanks.


        Larry Leitch

         


        ---In ccd-newastro@yahoogroups.com, <s24man@...> wrote:

        Ron,


        You're right, I meant "darks" not "flats", and no doubt there are better statistical methods to use.  I'm not someone who just likes to push buttons and watch things go without understanding really what I'm doing.  


        CCD stack has three ways to combine dark images.  A simple mean, a min-max clip and sigma reject mean.  The first two I understand, and the third I don't--yet.  (And I believe Pixinsight has a few more options).   I'm slowly dissecting Adam's videos because he's very good at explaining what he does--but he hasn't the time to go over absolutely everything.  


        Stu






        ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

        The bottom line is that there are probably better statistical methods for lowering the total noise in darks. (I presume you meant darks...)

        Ron Wodaski



        On Sep 26, 2013, at 9:47 AM, Stuart Forman <s24man@...> wrote:

         

        Thank you guys,  That's what I've been doing.  I've just been taking a lot of flats (a library of 40 or so) with the same integration time of the lights.  I just wanted to know if anybody was doing it the way Adam was talking about, and if there was an advantage to it. 
         
        Regards
        Stuart




      • lmleitch02
        Thanks Guys, Good info. Ron, About the one electron / hour. Is that one electron/hour/pixel? One per the whole chip? Larry ---In ccd-newastro@yahoogroups.com,
        Message 3 of 22 , Sep 28, 2013
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          Thanks Guys, Good info.


          Ron,

          About the one electron / hour. Is that one electron/hour/pixel? One per the whole chip?


          Larry

           



          ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

          Colder temps are always beneficial, but only so long as the camera's cooler can maintain that temperature in a stable way. If your camera is using 95% of it's cooling capacity, it doesn't have enough headroom to keep the temperature stable. For most amateur cameras, 80% of capacity is a reasonable max - and I usually like to be at 70% for really long exposures, but that's pretty conservative.

          Professional cameras and high-end amateur cameras tend to always keep extra capacity in reserve; they don't even let you approach 100% of capacity. 

          As Stan noted, QE is QE; it's not affected by temperature. 

          What lower temperature buys you, mostly, is lower noise, mostly in the form of lower dark current. Professional cameras are run at extremely low temps for this reason. Our Princeton Instruments Pixis camera has less than one electron per hour of dark current, for example. If the camera is also designed either with a very large full well or very low read noise, then you also get much better dynamic range, which allows you to use shorter (sometimes much shorter) exposures, which improve efficiency.

          Ron Wodaski



          On Sep 28, 2013, at 4:24 AM, k3fit@... wrote:

           

          Related question: What temperature should you set your camera to? As low as it will go? 

          Does quantum efficiency drop off as temperature decreases?


          Thanks.


          Larry Leitch

           


          ---In ccd-newastro@yahoogroups.com, <s24man@...> wrote:

          Ron,


          You're right, I meant "darks" not "flats", and no doubt there are better statistical methods to use.  I'm not someone who just likes to push buttons and watch things go without understanding really what I'm doing.  


          CCD stack has three ways to combine dark images.  A simple mean, a min-max clip and sigma reject mean.  The first two I understand, and the third I don't--yet.  (And I believe Pixinsight has a few more options).   I'm slowly dissecting Adam's videos because he's very good at explaining what he does--but he hasn't the time to go over absolutely everything.  


          Stu






          ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

          The bottom line is that there are probably better statistical methods for lowering the total noise in darks. (I presume you meant darks...)

          Ron Wodaski



          On Sep 26, 2013, at 9:47 AM, Stuart Forman <s24man@...> wrote:

           

          Thank you guys,  That's what I've been doing.  I've just been taking a lot of flats (a library of 40 or so) with the same integration time of the lights.  I just wanted to know if anybody was doing it the way Adam was talking about, and if there was an advantage to it. 
           
          Regards
          Stuart




        • Ron Wodaski
          The actual specification is quoted thus: 0.005 electron/pixel/second. Shortened link to data sheet: http://goo.gl/AsFkxk Ron Wodaski
          Message 4 of 22 , Sep 28, 2013
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            The actual specification is quoted thus: 0.005 electron/pixel/second. Shortened link to data sheet:

            http://goo.gl/AsFkxk

            Ron Wodaski



            On Sep 28, 2013, at 11:17 AM, k3fit@... wrote:

             

            Thanks Guys, Good info.


            Ron,

            About the one electron / hour. Is that one electron/hour/pixel? One per the whole chip?


            Larry

             


            ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

            Colder temps are always beneficial, but only so long as the camera's cooler can maintain that temperature in a stable way. If your camera is using 95% of it's cooling capacity, it doesn't have enough headroom to keep the temperature stable. For most amateur cameras, 80% of capacity is a reasonable max - and I usually like to be at 70% for really long exposures, but that's pretty conservative.

            Professional cameras and high-end amateur cameras tend to always keep extra capacity in reserve; they don't even let you approach 100% of capacity. 

            As Stan noted, QE is QE; it's not affected by temperature. 

            What lower temperature buys you, mostly, is lower noise, mostly in the form of lower dark current. Professional cameras are run at extremely low temps for this reason. Our Princeton Instruments Pixis camera has less than one electron per hour of dark current, for example. If the camera is also designed either with a very large full well or very low read noise, then you also get much better dynamic range, which allows you to use shorter (sometimes much shorter) exposures, which improve efficiency.

            Ron Wodaski



            On Sep 28, 2013, at 4:24 AM, k3fit@... wrote:

             

            Related question: What temperature should you set your camera to? As low as it will go? 

            Does quantum efficiency drop off as temperature decreases?


            Thanks.


            Larry Leitch

             


            ---In ccd-newastro@yahoogroups.com, <s24man@...> wrote:

            Ron,


            You're right, I meant "darks" not "flats", and no doubt there are better statistical methods to use.  I'm not someone who just likes to push buttons and watch things go without understanding really what I'm doing.  


            CCD stack has three ways to combine dark images.  A simple mean, a min-max clip and sigma reject mean.  The first two I understand, and the third I don't--yet.  (And I believe Pixinsight has a few more options).   I'm slowly dissecting Adam's videos because he's very good at explaining what he does--but he hasn't the time to go over absolutely everything.  


            Stu






            ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

            The bottom line is that there are probably better statistical methods for lowering the total noise in darks. (I presume you meant darks...)

            Ron Wodaski



            On Sep 26, 2013, at 9:47 AM, Stuart Forman <s24man@...> wrote:

             

            Thank you guys,  That's what I've been doing.  I've just been taking a lot of flats (a library of 40 or so) with the same integration time of the lights.  I just wanted to know if anybody was doing it the way Adam was talking about, and if there was an advantage to it. 
             
            Regards
            Stuart






          • Gregory
            Curious, Is there such of a thing as USB2.0 noise? If so, and again, is there such of a thing as an ôupgradedö USB2.0 noise reduction? Finally, if all of
            Message 5 of 22 , Sep 28, 2013
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              Curious,
               
              Is there such of a thing as USB2.0 noise? If so, and again, is there such of a thing as an “upgraded” USB2.0 noise reduction? Finally, if all of this is true, then does USB3.0 go even farther??
               
              Thanks
              Gregory
              Gig Harbor, WA.
              It’s raining as usual, will I see ISON??? Yuck!
            • Mike Dodd
              ... I don t think you need to worry about USB noise. The noise occurs in the CCD chip, and when the data is transmitted, the transmission medium is
              Message 6 of 22 , Sep 28, 2013
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                Gregory wrote:
                > Is there such of a thing as USB2.0 noise? If so, and again, is there
                > such of a thing as an “upgraded” USB2.0 noise reduction? Finally, if all
                > of this is true, then does USB3.0 go even farther??

                I don't think you need to worry about USB "noise." The noise occurs in
                the CCD chip, and when the data is transmitted, the transmission medium
                is essentially noiseless, relevant to image data. I.e., there might be
                noise on the USB signal, but this is filtered out by the USB receiver.

                --
                Mike

                Mike Dodd
                http://astronomy.mdodd.com
                Louisa County, Virginia USA N37.58.23 W77.56.24
              • stan_ccd
                ... I don t think you need to worry about USB noise. The noise occurs in the CCD chip, and when the data is transmitted, the transmission medium is
                Message 7 of 22 , Sep 29, 2013
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                  USB electronic noise does not usually become image noise because of built-in error checking.  However, a bad (noisy or slow) USB connection can easily affect images from non-buffered cameras. If the USB/computer cannot keep up with CCD readout then the readout must pause or skip and either action impacts the image. A pause allows heat to build up in the readout register and a skip fractures the image.

                   

                  A common cause USB "noise" is an overly long USB cable, a slow switching USB hub or extender, or too many other USB devices sharing the same bus/interrupt. A common symptoms of bad USB is inconsistent wavy lines ("interference") .  If you suspect USB problems then remove hubs, extender, long cable and other devices that share the interrupt or bus.

                   

                  Stan



                  ---In ccd-newastro@yahoogroups.com, <mike@...> wrote:

                  Gregory wrote:
                  > Is there such of a thing as USB2.0 noise? If so, and again, is there
                  > such of a thing as an “upgraded” USB2.0 noise reduction? Finally, if all
                  > of this is true, then does USB3.0 go even farther??

                  I don't think you need to worry about USB "noise." The noise occurs in
                  the CCD chip, and when the data is transmitted, the transmission medium
                  is essentially noiseless, relevant to image data. I.e., there might be
                  noise on the USB signal, but this is filtered out by the USB receiver.

                  --
                  Mike

                  Mike Dodd
                  http://astronomy.mdodd.com
                  Louisa County, Virginia USA N37.58.23 W77.56.24
                • astroimagek
                  Ron, I was curious about how you operate your Pixis. The spec shows 0.005e-/p/sec @-60C. Read noise is listed as 3.5e- RMS at 100kHz and 12e- RMS at 2MHz. What
                  Message 8 of 22 , Sep 29, 2013
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                    Ron,


                    I was curious about how you operate your Pixis.  The spec shows 0.005e-/p/sec @-60C.  Read noise is listed as 3.5e- RMS at 100kHz and 12e- RMS at 2MHz.  What temperature do you typically cool the sensor to, and what read rate do you use for your imaging?  Does your measured performance equal or exceed the specs?  Published specs are sometimes purposefully conservative.


                    Kevin



                    ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

                    The actual specification is quoted thus: 0.005 electron/pixel/second. Shortened link to data sheet:

                    http://goo.gl/AsFkxk

                    Ron Wodaski



                    On Sep 28, 2013, at 11:17 AM, k3fit@... wrote:

                     

                    Thanks Guys, Good info.


                    Ron,

                    About the one electron / hour. Is that one electron/hour/pixel? One per the whole chip?


                    Larry

                     


                    ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

                    Colder temps are always beneficial, but only so long as the camera's cooler can maintain that temperature in a stable way. If your camera is using 95% of it's cooling capacity, it doesn't have enough headroom to keep the temperature stable. For most amateur cameras, 80% of capacity is a reasonable max - and I usually like to be at 70% for really long exposures, but that's pretty conservative.

                    Professional cameras and high-end amateur cameras tend to always keep extra capacity in reserve; they don't even let you approach 100% of capacity. 

                    As Stan noted, QE is QE; it's not affected by temperature. 

                    What lower temperature buys you, mostly, is lower noise, mostly in the form of lower dark current. Professional cameras are run at extremely low temps for this reason. Our Princeton Instruments Pixis camera has less than one electron per hour of dark current, for example. If the camera is also designed either with a very large full well or very low read noise, then you also get much better dynamic range, which allows you to use shorter (sometimes much shorter) exposures, which improve efficiency.

                    Ron Wodaski



                    On Sep 28, 2013, at 4:24 AM, k3fit@... wrote:

                     

                    Related question: What temperature should you set your camera to? As low as it will go? 

                    Does quantum efficiency drop off as temperature decreases?


                    Thanks.


                    Larry Leitch

                     


                    ---In ccd-newastro@yahoogroups.com, <s24man@...> wrote:

                    Ron,


                    You're right, I meant "darks" not "flats", and no doubt there are better statistical methods to use.  I'm not someone who just likes to push buttons and watch things go without understanding really what I'm doing.  


                    CCD stack has three ways to combine dark images.  A simple mean, a min-max clip and sigma reject mean.  The first two I understand, and the third I don't--yet.  (And I believe Pixinsight has a few more options).   I'm slowly dissecting Adam's videos because he's very good at explaining what he does--but he hasn't the time to go over absolutely everything.  


                    Stu






                    ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

                    The bottom line is that there are probably better statistical methods for lowering the total noise in darks. (I presume you meant darks...)

                    Ron Wodaski



                    On Sep 26, 2013, at 9:47 AM, Stuart Forman <s24man@...> wrote:

                     

                    Thank you guys,  That's what I've been doing.  I've just been taking a lot of flats (a library of 40 or so) with the same integration time of the lights.  I just wanted to know if anybody was doing it the way Adam was talking about, and if there was an advantage to it. 
                     
                    Regards
                    Stuart






                  • Ron Wodaski
                    We operate at -55C, and optimize for minimum read noise - slow. I haven done any metrics, but images are exceptionally clean. Never use dark frames. Sent from
                    Message 9 of 22 , Sep 29, 2013
                    • 0 Attachment
                      We operate  at -55C, and optimize for minimum read noise - slow.

                      I haven done any metrics, but images are exceptionally clean. Never use dark frames. 

                      Sent from my iPad

                      On Sep 29, 2013, at 9:08, knelson@... wrote:

                       

                      Ron,


                      I was curious about how you operate your Pixis.  The spec shows 0.005e-/p/sec @-60C.  Read noise is listed as 3.5e- RMS at 100kHz and 12e- RMS at 2MHz.  What temperature do you typically cool the sensor to, and what read rate do you use for your imaging?  Does your measured performance equal or exceed the specs?  Published specs are sometimes purposefully conservative.


                      Kevin



                      ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

                      The actual specification is quoted thus: 0.005 electron/pixel/second. Shortened link to data sheet:

                      http://goo.gl/AsFkxk

                      Ron Wodaski



                      On Sep 28, 2013, at 11:17 AM, k3fit@... wrote:

                       

                      Thanks Guys, Good info.


                      Ron,

                      About the one electron / hour. Is that one electron/hour/pixel? One per the whole chip?


                      Larry

                       


                      ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

                      Colder temps are always beneficial, but only so long as the camera's cooler can maintain that temperature in a stable way. If your camera is using 95% of it's cooling capacity, it doesn't have enough headroom to keep the temperature stable. For most amateur cameras, 80% of capacity is a reasonable max - and I usually like to be at 70% for really long exposures, but that's pretty conservative.

                      Professional cameras and high-end amateur cameras tend to always keep extra capacity in reserve; they don't even let you approach 100% of capacity. 

                      As Stan noted, QE is QE; it's not affected by temperature. 

                      What lower temperature buys you, mostly, is lower noise, mostly in the form of lower dark current. Professional cameras are run at extremely low temps for this reason. Our Princeton Instruments Pixis camera has less than one electron per hour of dark current, for example. If the camera is also designed either with a very large full well or very low read noise, then you also get much better dynamic range, which allows you to use shorter (sometimes much shorter) exposures, which improve efficiency.

                      Ron Wodaski



                      On Sep 28, 2013, at 4:24 AM, k3fit@... wrote:

                       

                      Related question: What temperature should you set your camera to? As low as it will go? 

                      Does quantum efficiency drop off as temperature decreases?


                      Thanks.


                      Larry Leitch

                       


                      ---In ccd-newastro@yahoogroups.com, <s24man@...> wrote:

                      Ron,


                      You're right, I meant "darks" not "flats", and no doubt there are better statistical methods to use.  I'm not someone who just likes to push buttons and watch things go without understanding really what I'm doing.  


                      CCD stack has three ways to combine dark images.  A simple mean, a min-max clip and sigma reject mean.  The first two I understand, and the third I don't--yet.  (And I believe Pixinsight has a few more options).   I'm slowly dissecting Adam's videos because he's very good at explaining what he does--but he hasn't the time to go over absolutely everything.  


                      Stu






                      ---In ccd-newastro@yahoogroups.com, <ccd-newastro@yahoogroups.com> wrote:

                      The bottom line is that there are probably better statistical methods for lowering the total noise in darks. (I presume you meant darks...)

                      Ron Wodaski



                      On Sep 26, 2013, at 9:47 AM, Stuart Forman <s24man@...> wrote:

                       

                      Thank you guys,  That's what I've been doing.  I've just been taking a lot of flats (a library of 40 or so) with the same integration time of the lights.  I just wanted to know if anybody was doing it the way Adam was talking about, and if there was an advantage to it. 
                       
                      Regards
                      Stuart






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