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Camera temperature for flats

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  • Joe Morris
    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
    Message 1 of 12 , Jan 6, 2009
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      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
    • 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 2 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 3 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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 12 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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