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Re: [ccd-newastro] Focusing

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  • Ron Wodaski
    I use roughly that method before I get FocusMax working on a new system. Ron Wodaski
    Message 1 of 20 , Apr 3, 2012
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      I use roughly that method before I get FocusMax working on a new system.

      Ron Wodaski



      On Apr 3, 2012, at 7:07 AM, Mike Dodd wrote:

      > Bob wrote:
      >> Achieving very precise focus using a Bahtinov mask visually is
      >> difficult. But using a grabber program to measure your error and make
      >> further tweaks can put you within a micron or two of perfect focus in
      >> a few minutes. Of course, it doesn't work remotely.
      >
      > I have remotely used MaxIm and my focuser's control software to achieve
      > good focus by manually emulating FocusMax.
      >
      > I choose a star, make a test exposure, and note MaxIm's FHWM for that
      > star. Then bump the focus position a few steps in one direction, make
      > another exposure and note the FWHM, and repeat.
      >
      > It doesn't take long to see if the star is becoming smaller or larger.
      > If larger, I reverse focuser direction and step backward. As a
      > confidence-builder, I might check that the FWHM is approximately the
      > same passing through the original position as it was at the start.
      >
      > Once I find the smallest FHWM, I'll step past it a bit to verify that
      > the star becomes larger, then step back to achieve the smallest star. As
      > I approach critical focus, I'll reduce the number of steps that the
      > focuser control software sends to the focuser on each "bump," so I don't
      > miss the best FHWM.
      >
      > I've used this procedure to manually focus remotely from inside my
      > house. The main difference from FocusMax is that it uses real-time star
      > images instead of a V-curve averaged from a dozen test runs.
      >
      > Why not give it a try?
      > --
      > Mike
      >
      > Mike Dodd
      > http://astronomy.mdodd.com
      > Louisa County, Virginia USA N37.58.23 W77.56.24
      >
      >
      > ------------------------------------
      >
      >
      >
      >
    • Ron Wodaski
      Which just goes to prove that no one method for _anything_ works for everyone. We all have our preferences. One s zeal for manual or motorized or remote
      Message 2 of 20 , Apr 3, 2012
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        Which just goes to prove that no one method for _anything_ works for everyone. We all have our preferences. One's zeal for manual or motorized or remote methods is one's own. <g>

        It's important to realize, in such a large group, that no matter how perfect a method seems for _you_, someone else is still going to like a different way to do something.

        If you get the results you want, yes, why worry. Even so, I think it's good to hear what other people are doing, you never know when you might wind up with different equipment or conditions and a tip you read here will come in handy.

        Ron Wodaski



        On Apr 3, 2012, at 7:48 AM, echesak@... wrote:

        > Funny about masks... I started focusing my Tak, with Maxim and the stock manual focuser. I would take for ever to settle to a value that I felt was the minimum. On nights with less than perfect seeing, this process was an even longer, less confident task. I had started using the mask, then switched to Maxim. But after a year of fiddling, and several bad focus sessions, I went back to a mask.
        >
        > I find that I can get very high confidence focus in about 1/4 the time it took me with Maxim and my manual focuser. I've never used a motorized focuser, but with a mask, I have little desire to try one. I'm not planning to remote image, nor is an observatory in my immediate future.
        >
        > I'll probably get eaten for making this comment, but why would you need to get within 5 or 10 microns, on a system with a CFZ of maybe 200+ microns? Even with my 55 micron CFZ, I find that the mask works really well for me. Quick, confident focus, pinpoint/pixel-size stars in every image. I'm not saying its the best way, just the way that works best for me & my set-up.
        >
        > Eric
        >
        >
        >
        > --- In ccd-newastro@yahoogroups.com, "CurtisC" <calypte@...> wrote:
        >>
        >> I found it quite easy with my scopes. It's certainly better than watching dancing "brightest pixel" values. I like FocusMax, but I don't think the OP should stop imaging while he tries to get FocusMax working, which it may not with some equipment.
        >>
        >> --- In ccd-newastro@yahoogroups.com, "Bob" <tekic545@> wrote:
        >>>
        >>> Achieving very precise focus using a Bahtinov mask visually is difficult. But using a grabber program to measure your error and make further tweaks can put you within a micron or two of perfect focus in a few minutes. Of course, it doesn't work remotely.
        >>>
        >>> Bob
        >>
        >
        >
        >
        >
        > ------------------------------------
        >
        >
        >
        >
      • Michael Miller
        Don Goldman (Astrodon) told me that I should refocus my refractor every 30 minutes during the first 4-5 hours of the night as the air cools, and I kept mine
        Message 3 of 20 , Apr 3, 2012
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          Don Goldman (Astrodon) told me that I should refocus my refractor every 30 minutes during the first 4-5 hours of the night as the air cools, and I kept mine outside all the time. His suggestion was for optimal focus. Also a thing to remember is filter offsets. Even his outstanding generation 2 filters require some offset. I saw an increase in detail and a more consistent FWHM when following his advice. That can be critical when stacking images to increase color consistency in stars when combining RGB's. Also light refraction changes with altitude of the DSO. I'm guessing that altitude would have an effect on seeing (amount of air you're looking through) and that might effect focus as well. Stan would probably be an expert on that. I'm sure color changes from refraction which is why Don says to measure a G2V star near the DSO you're shooting.

          Michael D Miller
          CEO VP Services


          On Apr 3, 2012, at 1:37 AM, "Emile-Marie Pulinx" <e_pulinx@...> wrote:

          > Hi everybody
          >
          > I learned years ago that temperature changes during the night can cause focal shift of the scope.
          >
          > But,oddly, I never noticed that was for relevance for me ,even during long pauses ?
          >
          > I'm focusing at the beginning of a new session for a particular filter ,with the help of the "Prism" software ,before calibration and auto-guiding,and that's all !
          >
          > I have a refractor (Taka FS-128) since the beginning ,under a dome.
          >
          > Does a refractor have a lesser sensitivity that a scope for this phenomenon?
          >
          > cheers
          > Emil
          >
          > [Non-text portions of this message have been removed]
          >
          >


          [Non-text portions of this message have been removed]
        • Michael Miller
          Well said, those of us fortunate enough to be on a fixed pier and have complete automation would find it very difficult to manually mess with things. I guess
          Message 4 of 20 , Apr 3, 2012
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            Well said, those of us fortunate enough to be on a fixed pier and have complete automation would find it very difficult to manually mess with things. I guess ACP has spoiled me too much. Set up the plan, let it run and forget about it. I don't think I could go back to tearing down and setting up each night. I like my sleep too much. Of course I have awoken to find focusmax somehow got lost and I end up with one color set full of stars that look like doughnuts, so nothing ever works perfectly.

            Michael D Miller
            CEO VP Services


            On Apr 3, 2012, at 7:35 AM, Ron Wodaski <yahoo@...> wrote:

            > Which just goes to prove that no one method for _anything_ works for everyone. We all have our preferences. One's zeal for manual or motorized or remote methods is one's own. <g>
            >
            > It's important to realize, in such a large group, that no matter how perfect a method seems for _you_, someone else is still going to like a different way to do something.
            >
            > If you get the results you want, yes, why worry. Even so, I think it's good to hear what other people are doing, you never know when you might wind up with different equipment or conditions and a tip you read here will come in handy.
            >
            > Ron Wodaski
            >
            > On Apr 3, 2012, at 7:48 AM, echesak@... wrote:
            >
            > > Funny about masks... I started focusing my Tak, with Maxim and the stock manual focuser. I would take for ever to settle to a value that I felt was the minimum. On nights with less than perfect seeing, this process was an even longer, less confident task. I had started using the mask, then switched to Maxim. But after a year of fiddling, and several bad focus sessions, I went back to a mask.
            > >
            > > I find that I can get very high confidence focus in about 1/4 the time it took me with Maxim and my manual focuser. I've never used a motorized focuser, but with a mask, I have little desire to try one. I'm not planning to remote image, nor is an observatory in my immediate future.
            > >
            > > I'll probably get eaten for making this comment, but why would you need to get within 5 or 10 microns, on a system with a CFZ of maybe 200+ microns? Even with my 55 micron CFZ, I find that the mask works really well for me. Quick, confident focus, pinpoint/pixel-size stars in every image. I'm not saying its the best way, just the way that works best for me & my set-up.
            > >
            > > Eric
            > >
            > >
            > >
            > > --- In ccd-newastro@yahoogroups.com, "CurtisC" <calypte@...> wrote:
            > >>
            > >> I found it quite easy with my scopes. It's certainly better than watching dancing "brightest pixel" values. I like FocusMax, but I don't think the OP should stop imaging while he tries to get FocusMax working, which it may not with some equipment.
            > >>
            > >> --- In ccd-newastro@yahoogroups.com, "Bob" <tekic545@> wrote:
            > >>>
            > >>> Achieving very precise focus using a Bahtinov mask visually is difficult. But using a grabber program to measure your error and make further tweaks can put you within a micron or two of perfect focus in a few minutes. Of course, it doesn't work remotely.
            > >>>
            > >>> Bob
            > >>
            > >
            > >
            > >
            > >
            > > ------------------------------------
            > >
            > >
            > >
            > >
            >
            >


            [Non-text portions of this message have been removed]
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