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  1. #1
    Ernie's Avatar
    Ernie Guest

    Default Computerized Dobsonian mounts and astrophotography?



    I'm still new to astronomy, and buying the Dob I want is still a little
    ways away, and astrophotography is a long ways away from that, but my
    question is still one lurking in my mind with regards to whether or not
    computerized Dobsonian mounts are what I'm looking for.

    I understand that Dobs are exceptionally stable in comparison to, well,
    everything, and I'd expect that the alt-azimuth tracking motors on a
    computerized Dob wouldn't create a lot of vibration, while many
    equatorial mounts are plagued by vibration problems. Then there's the
    issue of the weight of the beast. Equatorial mounts have a definite
    weight limit that keep out larger newtonians or even SCTs.

    Is astrophotography on a computerized Dob feasible? I can't help but to
    wonder how the pros do their extended exposure shots with large
    ground-based telescopes, since their mounts use the same principle.

    --
    Mamma, the President's a fool | See that address up there? It's not real.
    Why do I have to keep | If you wanna send me email, send it to
    reading these technical manuals? | the same username at lightspeed.ca

  2. #2
    BllFs6's Avatar
    BllFs6 Guest

    Default Computerized Dobsonian mounts and astrophotography?

    >Is astrophotography on a computerized Dob feasible? I can't help but to

    Yep...very feasible and can actually be done pretty cheaply....particularly if
    you are somewhat mechanically/construction oriented.....

    Below is the info you need for motorized dob group....

    try a google search on "mel bartels motorized dob"

    enough info in that group to do anything your heart desires!

    take care

    Blll




    st message: scope-drive@yahoogroups.com


  3. #3
    Jon Isaacs's Avatar
    Jon Isaacs Guest

    Default Computerized Dobsonian mounts and astrophotography?

    >Is astrophotography on a computerized Dob feasible?

    Photography requires an EQ mount or an EQ Platform. Used with DOBs, EQ
    platforms can be used to do astrophotography.


    http://www201.pair.com/resource/astr.../eq_platforms/

    Normally a computerized scope is operated in the ALT-AZ mode which means that
    there will be field rotation even though the center of the Field of View tracks
    properly.

    The way around this is to use a derotator which is what the big boys use. The
    commonly available field derotator is the Meade unit, about $300 or so, rumour
    has it that it ain't that great.

    Here's some photos taken by S.A.A.'s own Del Johnson using a Tom Osypowski.
    Tom's seem to be the best...

    You might be shocked at the prices of these Platforms, they can run $3000 or so
    for a dual axis platform for a 20+ inch scope..

    But when compared to other solutions for mounting large scopes, they are
    amazingly inexpensive.



    See above.

    Jon


  4. #4
    vic20owner's Avatar
    vic20owner Guest

    Default Computerized Dobsonian mounts and astrophotography?

    Jon Isaacs wrote:

    Not necessarily. You can easily do some ccd and piggy back without an
    EQ mount as long as you have some form of alt/az tracking, and a way to
    stack the images. Some software will even de-rotate and align the
    images while stacking. I took some nice images of Saturn and the moon in
    alt/az mode on my first attempt. I can't do deepsky because my ccd
    camera isn't sensitive enough.

    Long exposures and serious deepsky is going to require a field derotator
    or eq mount mentioned in Jon's post. Field derotation is built into
    Mel's dob driver circuit and sofware. No experience using Mel's board.
    I built one but never ended up using it. I know of Mel from years ago
    in the telescope making forums. Have always heard great things about
    his software and driver board.

    -tom

  5. #5
    David Nakamoto's Avatar
    David Nakamoto Guest

    Default Computerized Dobsonian mounts and astrophotography?

    You'll need a field derotator, but that's available. Do a google and you
    should find them. The bigger question may be whether the tracking is good
    enough. If the camera software does autoguiding, and if the mount's drives
    accept the commands, then this should counter this problem.

    I'm beginning to believe that unless there's a major problem using the field
    derotator, with the current crop of cameras available to the amateur and the
    better dob computerized drives, that this might be a good alternative to the
    problem of accurately polar aligning an equatorial mount, not to mention the
    added weight such a mount means.

    --
    Yours Truly,
    --- Dave

    ----------------------------------------------------------------------
    'raid if you're afraid you'll have to overlook it.
    Besides, you knew the job was dangerous when you took it.
    ----------------------------------------------------------------------

    "Ernie" <gromm@bofh.lightspeed.ca> wrote in message
    news:4138e5fd@rsl2.rslnet.net...



  6. #6
    Jon Isaacs's Avatar
    Jon Isaacs Guest

    Default Computerized Dobsonian mounts and astrophotography?

    >I'm beginning to believe that unless there's a major problem using the field

    From what I have picked up here and else where, the Meade field derotator is
    not that great.

    jon

  7. #7
    Jon Isaacs's Avatar
    Jon Isaacs Guest

    Default Computerized Dobsonian mounts and astrophotography?

    >Not necessarily. You can easily do some ccd and piggy back without an

    True, but then one can take images of the moon and planets without even a
    tracking mount. The moon is easy.

    jon

  8. #8
    Chris1011's Avatar
    Chris1011 Guest

    Default Computerized Dobsonian mounts and astrophotography?

    >You'll need a field derotator, but that's available. Do a google and you

    The other question is, how well does it work around the zenith, where the best
    seeing and transparency occurs?

    Roland christen

  9. #9
    Ernie Dunbar's Avatar
    Ernie Dunbar Guest

    Default Computerized Dobsonian mounts and astrophotography?

    On 04 Sep 2004 15:37:08 GMT, chris1011@aol.com (Chris1011) wrote:


    That's easy, if you're using a Dobsonian mount. The Meade field
    derotator seems to be built for the Meade Schmidt-Cassegrain scopes on
    a fork mount, and it's irritating when the mount gets in the way at
    the zenith. But Newtonians on Dobsonian mounts fix this problem, just
    like they do for observing in general.


  10. #10
    Chris L Peterson's Avatar
    Chris L Peterson Guest

    Default Computerized Dobsonian mounts and astrophotography?

    On Sun, 05 Sep 2004 14:32:44 -0700, Ernie Dunbar
    <gromm@NO.SPAM.lightspeed.THANKS.ca> wrote:


    An altaz mount is an altaz mount, whether it is a Dob or a fork. In either case,
    the field rotation rate is infinite at the zenith. Tracking at the zenith is
    impossible for an altaz telescope. The maximum speed of the tracking motors and
    field derotator determine how close you can actually get to the zenith.

    If there are any mechanical misalignments in the mount (for example, if the axes
    are not perfectly orthogonal) there will even be coordinates near the zenith
    that are impossible to aim the scope at.

    These situations are similar for equatorial mounts near the pole, but that is a
    region of the sky that is usually easier to ignore than the zenith.

    _________________________________________________

    Chris L Peterson
    Cloudbait Observatory
    http://www.cloudbait.com

 

 
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