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TCF-S (Maxim settings question)

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  • randy_nulman
    Ron & group, Just received my TCF-S (using on C11 with .63 reducer...the reducer is attached to back, camera side, of focuser) First question is manual or
    Message 1 of 2 , Feb 2, 2002
      Ron & group,

      Just received my TCF-S (using on C11 with .63 reducer...the reducer
      is attached to back, camera side, of focuser)

      First question is manual or autofocusing (Maxim's routine):
      Since my seeing is a little choppy most of the time, (even on a good
      night the fwhm/half flux diam. may get down to 3 or lower, but with
      frequent jumps to say 4 or so)..Therefore, I'm wondering if there are
      enough iterations for Maxim to get a "true" best focus reading vs.
      continuing to focus manually? My thought is that I have the ability
      to know what "seeing jumps" are and disregard them...but the software
      won't be able to do this without _a lot_ of iterations to produce a
      good average.

      (I don't image remotely, so I'm at the scope anyway..and if I can do
      a more precise job manually I'm willing to do it. It ends up taking
      about 15 to 20 minutes total to do it manually...because of the
      number of iterations _I_ do to attempt to get perfect focus.)

      Secondly, if the consensus is that Maxim's autofocus routine will
      work just fine, I have a settings question:

      If the reducer is behind the focuser, my logic tells me that I should
      set the focal ratio to 6.3 since this is the effective focal ratio
      the chip, image and software look at. However, Doug George posted on
      the Maxim group that if the focuser is "scope side" of the reducer,
      it needs to be set to operate at F10. (even though a reducer is
      attached behind it)...ANY THOUGHTS ON THIS?? (His specific logic was
      that adding a reducer/camera behind the focuser is no different than
      removing the reducer and using a different camera with larger pixels.
      And, therefore feels the focuser should operate at F10 settings)
      I don't quite follow or agree with this logic.

      Thanks in advance,
      Randy Nulman
    • Steve Brady
      Randy-- You may want to download FocusMax at www.focusmax.org and give it a try with your Optec system, its free! Larry & I developed the Half Flux Diameter
      Message 2 of 2 , Feb 2, 2002
        Randy--

        You may want to download FocusMax at www.focusmax.org and give it a try with
        your Optec system, its free! Larry & I developed the Half Flux Diameter
        (HFD) metric concept over a year ago which has been incorporated in MaxIm
        'SharpStar' and FocusAid. FocusMax requires a little up front work to
        'train' the system for each unique optical configuration you will be using -
        BUT its worth it! I can focus my 10" Newtonian that uses RoboFocus in 25
        seconds with my Apogee camera and less than 50 seconds with a SBIG camera
        attached to an 8" LX200. To your question concerning seeing, HFD is defined
        as the diameter of a circle that is centered on the unfocused star image in
        which half of the total star flux is inside the circle and half is outside.
        The HFD gives a single number, in units of CCD pixels, that is relatively
        insensitive to variations in seeing, star flux, thin clouds or sky
        background glow. We have found this one metric to be accurate over a very
        wide range of unfocused star diameters and flux intensities because the HFD
        is determined by integrating all of the flux from the unfocused star area.
        HFD does not suffer from the problems found with gaussian fits or FWHM. We
        have a setting that allows the user to set how many exposures they wish to
        take before the focuser moves to the focus position, if the seeing is poor,
        increase the setting from a default of 5 subframes to 8 - 10, but from our
        experience, you may not have to do this.

        FocusMax is ASCOM compliant and contains a rich set of methods and
        properties that can be used in a custom script. An example is included which
        can be modified to be used with a filter wheel to determine the optical
        thickness of your filter set which can then be used to compensate the step
        position of the focuser for each filter used.

        FocusMax sill automatically find a target star in an image for the focus
        routine.We have also included a 'Select' feature which allows you to select
        a star for focusing. I was able to achieve perfect focus in less than 30
        seconds using a 50x50 subframe, a 0.1 sec exposure and selecting a moon of
        Jupiter. This is handy in rich star fields. Oh possibilities!

        To learn more about FocusMax, check out the presentations we gave at the Am
        / Pro Minor Planet and Imaging the Sky conferences last year.


        Ron --
        You remember the life autofocus demo we gave at the ITS conference!


        Steve Brady
        830 Hudson



        ----- Original Message -----
        From: "randy_nulman" <rjnulman@...>
        To: <ccd-newastro@yahoogroups.com>
        Sent: Saturday, February 02, 2002 10:23 AM
        Subject: [ccd-newastro] TCF-S (Maxim settings question)


        > Ron & group,
        >
        > Just received my TCF-S (using on C11 with .63 reducer...the reducer
        > is attached to back, camera side, of focuser)
        >
        > First question is manual or autofocusing (Maxim's routine):
        > Since my seeing is a little choppy most of the time, (even on a good
        > night the fwhm/half flux diam. may get down to 3 or lower, but with
        > frequent jumps to say 4 or so)..Therefore, I'm wondering if there are
        > enough iterations for Maxim to get a "true" best focus reading vs.
        > continuing to focus manually? My thought is that I have the ability
        > to know what "seeing jumps" are and disregard them...but the software
        > won't be able to do this without _a lot_ of iterations to produce a
        > good average.
        >
        > (I don't image remotely, so I'm at the scope anyway..and if I can do
        > a more precise job manually I'm willing to do it. It ends up taking
        > about 15 to 20 minutes total to do it manually...because of the
        > number of iterations _I_ do to attempt to get perfect focus.)
        >
        > Secondly, if the consensus is that Maxim's autofocus routine will
        > work just fine, I have a settings question:
        >
        > If the reducer is behind the focuser, my logic tells me that I should
        > set the focal ratio to 6.3 since this is the effective focal ratio
        > the chip, image and software look at. However, Doug George posted on
        > the Maxim group that if the focuser is "scope side" of the reducer,
        > it needs to be set to operate at F10. (even though a reducer is
        > attached behind it)...ANY THOUGHTS ON THIS?? (His specific logic was
        > that adding a reducer/camera behind the focuser is no different than
        > removing the reducer and using a different camera with larger pixels.
        > And, therefore feels the focuser should operate at F10 settings)
        > I don't quite follow or agree with this logic.
        >
        > Thanks in advance,
        > Randy Nulman
        >
        >
        >
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