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Re: Focus vs temperature Graph Request

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  • DaveH
    Holy cow...Serious bunch here ! I am going to love it ... Listen I thought there was all kinds of software that could reset/evaluate focus.. Not that I am that
    Message 1 of 21 , Mar 12 6:48 PM
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      Holy cow...Serious bunch here !
      I am going to love it ...
      Listen I thought there was all kinds of software that could reset/evaluate focus..
      Not that I am that high end...I take test shots and ran a cable to the house..
      So would that not be the way to go...setting up a periodic automated refocus...or was I dreaming ??

      Dave
      --- In ccd-newastro@yahoogroups.com, "Rick" <rickwiggins@...> wrote:
      >
      > Hi Don,
      > Since the data desired is how the scope foucus tracks with ambient temperature, you should take the ambient temperature as you pointed out. One thing to consider here is what you are trying to achieve. If you are imaging and you know what the outside temperature gradient will be, you could measure the outside temperature vs. focus behavior. Of course there will be lag and variation, but if you are gauging on outside temp, then measure that. I measure and track the temp in my dome and outside and I have a pretty good feel for how both will change and track over the night for given conditions.
      >
      > If you want to know what the scope does at various temps (i.e. how much the focus varies over temp), then you should measure the scope. As you point out, the scope has different materials in different thicknesses, so it will not track uniformly. In the lab, we instrument with many sensors to understand each area independently and learn the interrelationships over temp and temp rate change.
      >
      > I think the most important thing for us is the measurement that you suggested as that is probably the temp that most people measure and track.
      >
      > I will be interested in your results.
      > Thanks, Rick
    • Mike Dodd
      ... There are electric focusers that monitor the temperature of the OTA, and automatically adjust themselves according to calibration curves that you create
      Message 2 of 21 , Mar 12 7:51 PM
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        DaveH wrote:
        > Holy cow...Serious bunch here !
        > I am going to love it ...
        > Listen I thought there was all kinds of software that could reset/evaluate focus..
        > Not that I am that high end...I take test shots and ran a cable to the house..
        > So would that not be the way to go...setting up a periodic automated refocus...or was I dreaming ??

        There are electric focusers that monitor the temperature of the OTA, and
        automatically adjust themselves according to calibration curves that you
        create ahead of time.

        Another way to maintain good focus is to use automation software such as
        ACP or CCDAutoPilot that can be configured to periodically invoke a
        focusing program such as FocusMax to refocus the telescope.

        I believe that imaging programs such as CCDSoft and Maxim also have the
        ability to automatically focus, but I haven't used these features for
        many years.

        Automated focusing is not as trivial as it sounds. To achieve good
        focus, FocusMax or other software needs a suitable star, which might not
        be available in your camera's FOV for the target you're currently
        imaging. Consequently, the automation software or the focusing software
        must use a star catalog to identify a suitable star, slew the telescope
        to it, center it on the chip, perform the focusing operation, then slew
        back to your target and center it, all unattended.

        The choice is yours. If you don't mind staying up all night or getting
        up in the wee hours, it's perfectly reasonable to interrupt the imaging
        process and focus the telescope yourself. I did exactly this for several
        years. I set an alarm clock for just before my target was to transit,
        then got up and walked out to the observatory to perform the meridian
        flip on my German equatorial mount. Following this, I refocused,
        centered the target and resumed imaging. Then I went back to bed. With
        remote-control software on the observatory PC, I was able to do this
        from inside the house -- much more comfortable than going outside in
        15°F winter nights.

        Currently, though, I'm using ACP automation software, and this makes
        imaging soooo much more productive and enjoyable. Aside from the
        automatic periodic focusing, ACP's big benefit to me is its ability to
        accurately center by target on the chip. This alone saves me 5-10
        minutes at the beginning of imaging session, and another 5-10 minutes
        after the meridian flip.

        --
        Mike

        Mike Dodd
        Montpelier, VA USA
        http://astronomy.mdodd.com
        http://NotWhatIVotedFor.com
      • DaveH
        Mike Thanks for that info... I am one of the set the alarm clock crowd..and probably will be for some time..Doing it from inside is my only comfort. I
        Message 3 of 21 , Mar 13 3:41 AM
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          Mike
          Thanks for that info...
          I am one of the "set the alarm clock" crowd..and probably will be for some time..Doing it from inside is my only comfort.
          I avoid/fear complexity(and more software !)
          You have some very good results on your site.
          We are neighbors,(atmospherically),I am in Ottawa.

          Dave
        • Neil Fleming
          You re on the right path.  I ve always had more luck with refocusing than temperature compensation.  Just use FocusMax along with an automation program like
          Message 4 of 21 , Mar 13 7:46 AM
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            You're on the right path.  I've always had more luck with refocusing than temperature compensation.  Just use FocusMax along with an automation program like CCDCommander, CCDAutopilot, or ACP.  All three programs will let the software pick a star and go off and do a focus run, although I admit I prefer CCDC in this regard...as I can pick the focus star on my own, when I want it to happen.

               Cheers...Neil
             
            www.flemingastrophotography.com 
            Direct from Boston - brilliant diamonds in pea soup
            Also check out the astro_narrowbandYahoo group!




            ________________________________
            From: DaveH <davehalliday51@...>
            To: ccd-newastro@yahoogroups.com
            Sent: Fri, March 12, 2010 9:48:09 PM
            Subject: [ccd-newastro] Re: Focus vs temperature Graph Request

            Holy cow...Serious bunch here !
            I am going to love it ...
            Listen I thought there was all kinds of software that could reset/evaluate focus..
            Not that I am that high end...I take test shots and ran a cable to the house..
            So would that not be the way to go...setting up a periodic automated refocus...or was I dreaming ??

            Dave
            --- In ccd-newastro@yahoogroups.com, "Rick" <rickwiggins@...> wrote:
            >
            > Hi Don,
            > Since the data desired is how the scope foucus tracks with ambient temperature, you should take the ambient temperature as you pointed out. One thing to consider here is what you are trying to achieve. If you are imaging and you know what the outside temperature gradient will be, you could measure the outside temperature vs. focus behavior. Of course there will be lag and variation, but if you are gauging on outside temp, then measure that. I measure and track the temp in my dome and outside and I have a pretty good feel for how both will change and track over the night for given conditions.
            >
            > If you want to know what the scope does at various temps (i.e. how much the focus varies over temp), then you should measure the scope. As you point out, the scope has different materials in different thicknesses, so it will not track uniformly. In the lab, we instrument with many sensors to understand each area independently and learn the interrelationships over temp and temp rate change.
            >
            > I think the most important thing for us is the measurement that you suggested as that is probably the temp that most people measure and track.
            >
            > I will be interested in your results.
            > Thanks, Rick


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