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Re: Camera temperature for flats

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  • Rick Wiggins
    Hi Joe, I hope Ron answers this also as he has spent significant time regarding the darks for flats issue. IMHO, it is always a good idea to take any
    Message 1 of 12 , Jan 6, 2009
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      Hi Joe,
      I hope Ron answers this also as he has spent significant time
      regarding the darks for flats issue.

      IMHO, it is always a good idea to take any calibration frames under
      teh same set of circumstances as when you are imaging. The more things
      that don't vary the better. The only real issue regarding flats at
      temperature is that the bias level, temperature gradient on the chip,
      or variation in temperatures of the sampling and digitization
      circuitry in the camera might be different at temperature. The effects
      of this would probably be so far below the limiting noise contributors
      that they may not even affect the final image; however, why not just
      take them all under the same conditions. I run everything the same as
      when I am imaging (do it at night, in the dark, at temp., with my dew
      heaters and guider running and cooled to the same temp as when
      imaging. This is easy for those with permanent setups. For my
      traveling setup, I can't always do this so I may take darks and even
      flats at another time and with a slightly different configuration
      (critical to have the camera, filters, and optical path be identical).

      Regarding subtracting darks or Bias from flats, I beleive that depends
      on how many flats that you take. If you take 10 sec flats and have 30
      to average per filter, then subtracting a master 10 sec dark or even
      bias from the master flat, may lower the noise in the final master
      flat. If you have only 4 flats to average and a few darks or bias
      frames, then subtracting them from the flat will probably increase the
      noise in the Master flat and not help.

      Hopefully, Ron can quantify my subjective data.
      Thanks, Rick



      --- In ccd-newastro@yahoogroups.com, "Joe Morris" <joemorris@...>
      wrote:
      >
      > Is there any advantage in taking flats with the CCD at the same
      > temperature that the LRGB images were taken? If the flats are all
      > between 1 and 10 seconds, is it worth the effort to take darks or is
      > bias subtraction satisfactory?
      >
      > Joe
      >
    • Paul K
      Joe, There s no need to take flats at the same temperature. The signal level in a 10 second flat is so much above any dark current that the temperature is
      Message 2 of 12 , Jan 6, 2009
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        Joe,

        There's no need to take flats at the same temperature. The signal level
        in a 10 second flat is so much above any dark current that the
        temperature is really irrelevant.

        For a 10 second flat, a bias subtraction is all that's needed, because
        again, the dark current will be tiny in comparison to flat signal. The
        point of subtracting bias from a flat is to remove any large constant
        offset in pixel adu levels.

        For certain cameras where bias level is low (100adu), bias subtraction
        is also not strictly speaking needed. Other cameras, with the bias
        level above 1000adu will benefit from a flat bias subtraction.

        Regards,

        -Paul

        --- In ccd-newastro@yahoogroups.com, "Joe Morris" <joemorris@...> wrote:
        >
        > Is there any advantage in taking flats with the CCD at the same
        > temperature that the LRGB images were taken? If the flats are all
        > between 1 and 10 seconds, is it worth the effort to take darks or is
        > bias subtraction satisfactory?
        >
        > Joe
        >
      • Mark de Regt
        Hi, I have a friend who lives on Long Island Sound, and would like to buy a spotting scope for looking out at the boats. He does not plan to use it for
        Message 3 of 12 , Jan 7, 2009
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          Hi,

          I have a friend who lives on Long Island Sound, and would like to buy a
          spotting scope for looking out at the boats. He does not plan to use it for
          astronomical purposes.

          I used to own an ETX-90, which would be perfect optically for what he wants.
          But the mount was unsteady, and he doesn't need to pay for GOTO.

          I'm looking for suggestions for a cost-effective (he can pay for good, but
          there's no reason, for instance, for him to buy a Tak Sky90 for this
          purpose) system of scope and mount/tripod for him.

          Thanks!

          --Mark
        • FocusKnobs
          If you think the ETX-90 would be ok, get an ETX-90 spotting scope. It will mount on any good photo tripod. I m sure you could find one cheap on Astromart. Lou
          Message 4 of 12 , Jan 7, 2009
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            If you think the ETX-90 would be ok, get an ETX-90 spotting scope. It
            will mount on any good photo tripod. I'm sure you could find one cheap
            on Astromart.

            Lou

            -----Original Message-----
            From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com]
            On Behalf Of Mark de Regt
            Sent: Wednesday, January 07, 2009 8:59 AM
            To: ccd-newastro@yahoogroups.com
            Subject: [ccd-newastro] OT: Spotting Scope

            Hi,

            I have a friend who lives on Long Island Sound, and would like to buy a
            spotting scope for looking out at the boats. He does not plan to use it
            for
            astronomical purposes.

            I used to own an ETX-90, which would be perfect optically for what he
            wants.
            But the mount was unsteady, and he doesn't need to pay for GOTO.

            I'm looking for suggestions for a cost-effective (he can pay for good,
            but
            there's no reason, for instance, for him to buy a Tak Sky90 for this
            purpose) system of scope and mount/tripod for him.

            Thanks!

            --Mark
          • Yahoo - Wodaski
            ... Optical quality is optical quality - there s no reason for someone NOT to buy a quality optic for viewing terrestrially, either. One is looking through
            Message 5 of 12 , Jan 7, 2009
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              >> there's no reason, for instance, for him to buy a Tak Sky90

              Optical quality is optical quality - there's no reason for someone NOT
              to buy a quality optic for viewing terrestrially, either. <g> One is
              looking through quite a bit more air currents along the ground, but a
              good optic does deal with seeing issues better than a poor optic.

              Having lived along the coast and used several telescopes for this kind
              of viewing, high quality optics does pay a dividend.

              Still, the cost premium for, say, an APO is pretty high. I just want to
              emphasize that it's not that there is no difference in performance. A 4"
              APO is lovely in this application, just as it is lovely for night viewing!

              With that in mind, if one wants to spend a limited amount of money, a
              regular spotting scope should be on the list for consideration. The main
              reason to buy an astronomical telescope would be for optical quality;
              spotting scopes may well prove to have more conveniences because they
              are after all purpose built! <G>

              I don't particularly care for mirror lenses/scopes for terrestrial
              viewing; you get odd out-of-focus artifacts from the secondary that are
              not as pleasing as what you get with a refractor. Again, however, they
              are a cost-based compromise.

              Among the astronomy companies, TeleVue makes more of a commitment to
              terrestrial viewing and if you want a quality scope, look there - they
              will have scope/mount combos that will have very good quality. If you
              don't mind some chromatic issues, any inexpensive refractor will do the
              job at an attractive price; an alt-az mount will be all you need.

              Also look at a nice pair of image stabilized binocs (I have the Canons)
              - they would probably make a tripod unnecessary, and therefore are fun
              and easy to use, and provide modest but very clean magnification. This
              is what I've come to use for stuff like this. The only downside is the
              limited magnification; larger binocs and a binoc stand with
              counterbalancing would be the next step up in that department.

              Ron W

              Mark de Regt wrote:
              > Hi,
              >
              > I have a friend who lives on Long Island Sound, and would like to buy a
              > spotting scope for looking out at the boats. He does not plan to use it for
              > astronomical purposes.
              >
              > I used to own an ETX-90, which would be perfect optically for what he wants.
              > But the mount was unsteady, and he doesn't need to pay for GOTO.
              >
              > I'm looking for suggestions for a cost-effective (he can pay for good, but
              > there's no reason, for instance, for him to buy a Tak Sky90 for this
              > purpose) system of scope and mount/tripod for him.
              >
              > Thanks!
              >
              > --Mark
              >
              >
              >
              > ------------------------------------
              >
              >
              >
              >
            • Eric Africa
              Hi Mark, No arguments about Televue, but another make that you might want to consider would be the Borg series of scopes. They recently seem to be starting to
              Message 6 of 12 , Jan 7, 2009
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                Hi Mark,

                No arguments about Televue, but another make that you might want to consider would be the Borg series of scopes. They recently seem to be starting to market towards what they call the "Digiscoping" crowd - terrestrial long-focal-length photograhpy.

                A 77ED on an alt-az would be a nice one, or even a 101ED. Hmmm... they used to have complete alt-az packages on their website, but they must have discontinued those:

                http://www.sciencecenter.net/hutech/prlist.htm

                One additional nicety of the Borg series (in addition to being nice, light and portable) is that they allow for upgrade paths: if your friend starts out with a 77ED and decides he wants the 101ED, he can just swap out the 77ED objective with the 101ED.

                HTH,
                Eric



                To: ccd-newastro@yahoogroups.comFrom: deregt@...: Wed, 7 Jan 2009 08:59:03 -0800Subject: [ccd-newastro] OT: Spotting Scope



                Hi,I have a friend who lives on Long Island Sound, and would like to buy aspotting scope for looking out at the boats. He does not plan to use it forastronomical purposes.I used to own an ETX-90, which would be perfect optically for what he wants.But the mount was unsteady, and he doesn't need to pay for GOTO.I'm looking for suggestions for a cost-effective (he can pay for good, butthere's no reason, for instance, for him to buy a Tak Sky90 for thispurpose) system of scope and mount/tripod for him.Thanks!--Mark





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              • Yahoo - Wodaski
                Good suggestion. Forgot about Borg. TeleVue probably has the edge in alt-az mounts, however. Ron W
                Message 7 of 12 , Jan 7, 2009
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                  Good suggestion. Forgot about Borg. TeleVue probably has the edge in
                  alt-az mounts, however. <G>

                  Ron W

                  Eric Africa wrote:
                  > Hi Mark,
                  >
                  > No arguments about Televue, but another make that you might want to consider would be the Borg series of scopes. They recently seem to be starting to market towards what they call the "Digiscoping" crowd - terrestrial long-focal-length photograhpy.
                  >
                  > A 77ED on an alt-az would be a nice one, or even a 101ED. Hmmm... they used to have complete alt-az packages on their website, but they must have discontinued those:
                  >
                  > http://www.sciencecenter.net/hutech/prlist.htm
                  >
                  > One additional nicety of the Borg series (in addition to being nice, light and portable) is that they allow for upgrade paths: if your friend starts out with a 77ED and decides he wants the 101ED, he can just swap out the 77ED objective with the 101ED.
                  >
                  > HTH,
                  > Eric
                  >
                  >
                  >
                  > To: ccd-newastro@yahoogroups.comFrom: deregt@...: Wed, 7 Jan 2009 08:59:03 -0800Subject: [ccd-newastro] OT: Spotting Scope
                  >
                  >
                  >
                  > Hi,I have a friend who lives on Long Island Sound, and would like to buy aspotting scope for looking out at the boats. He does not plan to use it forastronomical purposes.I used to own an ETX-90, which would be perfect optically for what he wants.But the mount was unsteady, and he doesn't need to pay for GOTO.I'm looking for suggestions for a cost-effective (he can pay for good, butthere's no reason, for instance, for him to buy a Tak Sky90 for thispurpose) system of scope and mount/tripod for him.Thanks!--Mark
                  >
                  >
                  >
                  >
                  >
                  > _________________________________________________________________
                  > Windows LiveTM HotmailĀ®: Chat. Store. Share. Do more with mail.
                  > http://windowslive.com/explore?ocid=TXT_TAGLM_WL_t1_hm_justgotbetter_explore_012009
                  >
                  > [Non-text portions of this message have been removed]
                  >
                  >
                  > ------------------------------------
                  >
                  >
                  >
                  >
                • Mark de Regt
                  Thanks all for the excellent suggestions! ... From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com] On Behalf Of Yahoo - Wodaski Sent:
                  Message 8 of 12 , Jan 7, 2009
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                    Thanks all for the excellent suggestions!

                    -----Original Message-----
                    From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com] On
                    Behalf Of Yahoo - Wodaski
                    Sent: Wednesday, January 07, 2009 12:03 PM
                    To: ccd-newastro@yahoogroups.com
                    Subject: Re: [ccd-newastro] OT: Spotting Scope

                    Good suggestion. Forgot about Borg. TeleVue probably has the edge in
                    alt-az mounts, however. <G>

                    Ron W

                    Eric Africa wrote:
                    > Hi Mark,
                    >
                    > No arguments about Televue, but another make that you might want to
                    consider would be the Borg series of scopes. They recently seem to be
                    starting to market towards what they call the "Digiscoping" crowd -
                    terrestrial long-focal-length photograhpy.
                    >
                    > A 77ED on an alt-az would be a nice one, or even a 101ED. Hmmm... they
                    used to have complete alt-az packages on their website, but they must have
                    discontinued those:
                    >
                    > http://www.sciencecenter.net/hutech/prlist.htm
                    >
                    > One additional nicety of the Borg series (in addition to being nice, light
                    and portable) is that they allow for upgrade paths: if your friend starts
                    out with a 77ED and decides he wants the 101ED, he can just swap out the
                    77ED objective with the 101ED.
                    >
                    > HTH,
                    > Eric
                    >
                    >
                    >
                    > To: ccd-newastro@yahoogroups.comFrom: deregt@...: Wed, 7 Jan
                    2009 08:59:03 -0800Subject: [ccd-newastro] OT: Spotting Scope
                    >
                    >
                    >
                    > Hi,I have a friend who lives on Long Island Sound, and would like to buy
                    aspotting scope for looking out at the boats. He does not plan to use it
                    forastronomical purposes.I used to own an ETX-90, which would be perfect
                    optically for what he wants.But the mount was unsteady, and he doesn't need
                    to pay for GOTO.I'm looking for suggestions for a cost-effective (he can pay
                    for good, butthere's no reason, for instance, for him to buy a Tak Sky90 for
                    thispurpose) system of scope and mount/tripod for him.Thanks!--Mark
                    >
                    >
                    >
                    >
                    >
                    > _________________________________________________________________
                    > Windows LiveTM HotmailR: Chat. Store. Share. Do more with mail.
                    >
                    http://windowslive.com/explore?ocid=TXT_TAGLM_WL_t1_hm_justgotbetter_explore
                    _012009
                    >
                    > [Non-text portions of this message have been removed]
                    >
                    >
                    > ------------------------------------
                    >
                    >
                    >
                    >

                    ------------------------------------
                  • george hall
                    Don t forget WO. They make well made economical scopes. George ... [Non-text portions of this message have been removed]
                    Message 9 of 12 , Jan 7, 2009
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                      Don't forget WO. They make well made economical scopes.

                      George

                      On Jan 7, 2009, at 8:03 PM, Mark de Regt wrote:

                      > Thanks all for the excellent suggestions!
                      >
                      > -----Original Message-----
                      > From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com
                      > ] On
                      > Behalf Of Yahoo - Wodaski
                      > Sent: Wednesday, January 07, 2009 12:03 PM
                      > To: ccd-newastro@yahoogroups.com
                      > Subject: Re: [ccd-newastro] OT: Spotting Scope
                      >
                      > Good suggestion. Forgot about Borg. TeleVue probably has the edge in
                      > alt-az mounts, however. <G>
                      >
                      > Ron W
                      >
                      > Eric Africa wrote:
                      > > Hi Mark,
                      > >
                      > > No arguments about Televue, but another make that you might want to
                      > consider would be the Borg series of scopes. They recently seem to be
                      > starting to market towards what they call the "Digiscoping" crowd -
                      > terrestrial long-focal-length photograhpy.
                      > >
                      > > A 77ED on an alt-az would be a nice one, or even a 101ED. Hmmm...
                      > they
                      > used to have complete alt-az packages on their website, but they
                      > must have
                      > discontinued those:
                      > >
                      > > http://www.sciencecenter.net/hutech/prlist.htm
                      > >
                      > > One additional nicety of the Borg series (in addition to being
                      > nice, light
                      > and portable) is that they allow for upgrade paths: if your friend
                      > starts
                      > out with a 77ED and decides he wants the 101ED, he can just swap out
                      > the
                      > 77ED objective with the 101ED.
                      > >
                      > > HTH,
                      > > Eric
                      > >
                      > >
                      > >
                      > > To: ccd-newastro@yahoogroups.comFrom: deregt@...:
                      > Wed, 7 Jan
                      > 2009 08:59:03 -0800Subject: [ccd-newastro] OT: Spotting Scope
                      > >
                      > >
                      > >
                      > > Hi,I have a friend who lives on Long Island Sound, and would like
                      > to buy
                      > aspotting scope for looking out at the boats. He does not plan to
                      > use it
                      > forastronomical purposes.I used to own an ETX-90, which would be
                      > perfect
                      > optically for what he wants.But the mount was unsteady, and he
                      > doesn't need
                      > to pay for GOTO.I'm looking for suggestions for a cost-effective (he
                      > can pay
                      > for good, butthere's no reason, for instance, for him to buy a Tak
                      > Sky90 for
                      > thispurpose) system of scope and mount/tripod for him.Thanks!--Mark
                      > >
                      > >
                      > >
                      > >
                      > >
                      > > __________________________________________________________
                      > > Windows LiveTM HotmailR: Chat. Store. Share. Do more with mail.
                      > >
                      > http://windowslive.com/explore?ocid=TXT_TAGLM_WL_t1_hm_justgotbetter_explore
                      > _012009
                      > >
                      > > [Non-text portions of this message have been removed]
                      > >
                      > >
                      > > ------------------------------------
                      > >
                      > >
                      > >
                      > >
                      >
                      > ------------------------------------
                      >
                      >
                      >



                      [Non-text portions of this message have been removed]
                    • Roger Hamlett
                      ... The main thing wrong with the ETX-90, is that because it has the diagonal built in , views will be inverted. Normally for a spotting scope, you want a
                      Message 10 of 12 , Jan 8, 2009
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                        > Hi,
                        >
                        > I have a friend who lives on Long Island Sound, and would like to buy a
                        > spotting scope for looking out at the boats. He does not plan to use it for
                        > astronomical purposes.
                        >
                        > I used to own an ETX-90, which would be perfect optically for what he wants.
                        > But the mount was unsteady, and he doesn't need to pay for GOTO.
                        >
                        > I'm looking for suggestions for a cost-effective (he can pay for good, but
                        > there's no reason, for instance, for him to buy a Tak Sky90 for this
                        > purpose) system of scope and mount/tripod for him.
                        >
                        > Thanks!
                        The main thing 'wrong' with the ETX-90, is that because it has the
                        diagonal 'built in', views will be inverted. Normally for a spotting
                        scope, you want a 45 degree diagonal to give 'right way up' images.
                        Now, getting an APO, is a very good solution, but expensive for what you
                        get. Personally, why not look at the Celestron C5 spotter,
                        and add this to a really good pan/tilt photographic
                        tripod?. This is a combination I have used at the range for target
                        spotting, then with a lower power eyepiece, for watching boats. I use it
                        on a Manfrotto 055Pro with the 322 head. If weight is an issue, then
                        look at geting the 440 carbon fibre tripod instead.

                        Best Wishes
                      • Michael Perata
                        ... buy a ... use it for ... Having used a scopes on the water, I would suggest staying away from a Cat mainly because of the diminished contrast inherent in
                        Message 11 of 12 , Jan 8, 2009
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                          > >
                          > > I have a friend who lives on Long Island Sound, and would like to
                          buy a
                          > > spotting scope for looking out at the boats. He does not plan to
                          use it for
                          > > astronomical purposes.
                          > >

                          Having used a scopes on the water, I would suggest staying away from a
                          Cat mainly because of the diminished contrast inherent in the design.

                          If your friend truly will not want to look skyward, I would recommend
                          looking at the Nikons, Fujinon or for lower priced scopes, Bushnell.

                          Michael in San Jose
                          Ross Creek Observatory
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