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  1. #1
    Max's Avatar
    Max Guest

    Default Planetary imaging with fast Newtonian



    Hi all,

    I own an Orion SkyView Pro 8 EQ. The scope has an f/5 focal ratio so
    it's pretty fast. With Mars at his best, I started doing some imaging
    of the planet using a webcam. Even with a 2x Barlow the size of the
    planet disk is pretty small. I can see details, but not much. Of course
    that depends also on seeing conditions, but I had a couple of good
    nights this month. Collimation is also another factor with a fast scope
    like mine. Again, I made sure that the optics are indeed properly
    aligned to get the best possible images.

    It seems clear to me that if I want to get more detailed images I
    should try to increase the focal length somehow. As I mentioned, I
    already own a pretty decent barlow (Shorty-Plus™ 2x 3-Element
    Barlow). That lens brings the focal ratio to f/10, which is hardly
    enough. Since I can't afford to buy a Powermate 5x, I am thinking of
    purchasing a 3x barlow from Orion (Tri-Mag™ 3x Barlow Lens) and stack
    it on top of the 2x barlow. That would be equivalent to a 6x
    amplification factor and my scope would acquire an f/30 focal ratio.

    Would you recommend doing something like that? Would eyepiece
    projection a better way of achieving similar results? Or should I just
    wait until I can afford the Powermate?


  2. #2
    David Nakamoto's Avatar
    David Nakamoto Guest

    Default Planetary imaging with fast Newtonian

    I don't know of an easy way to fit eyepiece projection to most web cam telescope
    adapters, but if there is one, then that would be one way to go. The Barlow is
    the commonest way to go. But you're problem is the short focal length of the
    main telescope. And you're going to need as much focal length as you can get to
    image the small disk of Mars this opposition, less than 50% that of Jupiter, and
    even smaller than the disk of Saturn (not including the rings).

    Good Luck !

    --- Dave
    --
    ----------------------------------------------------------------------
    Pinprick holes in a colorless sky
    Let inspired figures of light pass by
    The Mighty Light of ten thousand suns
    Challenges infinity, and is soon gone

    david.nakamoto@verizon.net


    "Max" <mi97ki@yahoo.com> wrote in message
    news:1129411637.450665.153530@g43g2000cwa.googlegr oups.com...
    Hi all,

    I own an Orion SkyView Pro 8 EQ. The scope has an f/5 focal ratio so
    it's pretty fast. With Mars at his best, I started doing some imaging
    of the planet using a webcam. Even with a 2x Barlow the size of the
    planet disk is pretty small. I can see details, but not much. Of course
    that depends also on seeing conditions, but I had a couple of good
    nights this month. Collimation is also another factor with a fast scope
    like mine. Again, I made sure that the optics are indeed properly
    aligned to get the best possible images.

    It seems clear to me that if I want to get more detailed images I
    should try to increase the focal length somehow. As I mentioned, I
    already own a pretty decent barlow (Shorty-PlusT 2x 3-Element
    Barlow). That lens brings the focal ratio to f/10, which is hardly
    enough. Since I can't afford to buy a Powermate 5x, I am thinking of
    purchasing a 3x barlow from Orion (Tri-MagT 3x Barlow Lens) and stack
    it on top of the 2x barlow. That would be equivalent to a 6x
    amplification factor and my scope would acquire an f/30 focal ratio.

    Would you recommend doing something like that? Would eyepiece
    projection a better way of achieving similar results? Or should I just
    wait until I can afford the Powermate?



  3. #3
    jonisaacs@aol.com's Avatar
    jonisaacs@aol.com Guest

    Default Planetary imaging with fast Newtonian

    No need to buy a Powermate, stacking barlows works... A shorty Plus
    normally runs about 2.3x or so. Add another 2x barlow and you will be
    close to 5X.

    I know that Rod Mollise has done some planetary imaging with a
    Konus/Synta 8 inch F5 Newt and I think a SAC camera. You might give
    him a buzz.

    Jon


  4. #4
    RMOLLISE's Avatar
    RMOLLISE Guest

    Default Planetary imaging with fast Newtonian


    jonisaacs@aol.com wrote:


    Yep...and it worked very well.

    Yes, the primary problem is getting the focal ratio up...the optics are
    good. I resorted to stacking 2x and 3x barlows. However, if I were
    serious about using this OTA for hi-res planetary imaging on a regular
    basis, I probably would spring for a Powermate. While stacked barlows
    do work, they are incovenient and a might shakey.

    Peace,
    Rod Mollise
    Author of _Choosing and Using a Schmidt Cassegrain Telescope_

    Like SCTs and MCTs?
    Join the SCT User Mailing List.
    <http://www.groups.yahoo.com/group/sct-user>

    See my home page at
    <http://skywatch.brainiac.com/astroland/index.htm>
    for further info

    For Uncle Rod's Astro Blog See:
    <http://journals.aol.com/rmollise/UncleRodsAstroBlog/>


  5. #5
    Chris L Peterson's Avatar
    Chris L Peterson Guest

    Default Planetary imaging with fast Newtonian

    On 16 Oct 2005 10:27:11 -0700, "RMOLLISE" <rmollise@hotmail.com> wrote:


    At the risk of sounding like a broken record, focal ratio is not what we
    should be talking about here. What matters is only focal length, and for
    good webcam images something around 6000mm is a good target.

    Yes, he stated his aperture in the original post, so you can calculate
    focal length from focal ratio, but thinking in terms of focal ratio is
    just wrong, and should be avoided.

    _________________________________________________

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

  6. #6
    David Nakamoto's Avatar
    David Nakamoto Guest

    Default Planetary imaging with fast Newtonian

    I have to agree with part of this. Think about it; a focal length of 4000mm is
    going to produce the same image size on a given CCD no matter what the f/ratio
    is. From the standpoint of image scale, focal length is all you need. This
    also means that if you want to know the image scale your camera produces on
    different telescopes, all you need to do is take the ratio of the telescope's
    focal lengths. I've found that this works very well. So if you go from a focal
    length of 4000mm to one of 3000mm, and the FOV with your camera is 30
    arc-minutes, then the new FOV is 30 * 4/3 or 40 arc-minutes.

    But a 300mm f/5 system is brighter than a 127mm f/12 system, even though both
    are the same focal length and therefore produce the same FOV. This is important
    to chop down the exposure times and assist with "freezing out" seeing effects,
    making the individual images clearer and the resultant stack therefore clearer.
    But this is a function of aperture size, not focal ratio, as is the attendant
    aspect of image resolution clarity, the amount of detail possible to see in the
    images. The focal ratio is a combination of aperture and focal length, but
    while it unites the two, for purposes of planet imaging I can't see where JUST
    that number alone can tell you anything useful about the telescope you're using
    to image planets. You need to know the aperture and focal length.

    Sharing the Astronomy Experience,
    --- Dave
    --
    ----------------------------------------------------------------------
    Pinprick holes in a colorless sky
    Let inspired figures of light pass by
    The Mighty Light of ten thousand suns
    Challenges infinity, and is soon gone

    david.nakamoto@verizon.net


    "Chris L Peterson" <clp@alumni.caltech.edu> wrote in message
    news:rs35l15gk824o6t6gug64jnc08i6dsd6j9@4ax.com...



  7. #7
    jonisaacs@aol.com's Avatar
    jonisaacs@aol.com Guest

    Default Planetary imaging with fast Newtonian

    At the risk of sounding like a broken record, focal ratio is not what
    we should be talking about here. What matters is only focal length, and
    for good webcam images something around 6000mm is a good target.

    Yes, he stated his aperture in the original post, so you can calculate
    focal length from focal ratio, but thinking in terms of focal ratio is
    just wrong, and should be avoided.
    ---------------------

    I agree that what we are talking about here is getting that 8 inch FL
    1000mm scope up to 5000mm or 6000mm effective focal length. It's also
    good to know that it will be about F25/F30 when considering the
    exposure times.

    Jon...


  8. #8
    Chris L Peterson's Avatar
    Chris L Peterson Guest

    Default Planetary imaging with fast Newtonian

    On 17 Oct 2005 10:59:25 -0700, "jonisaacs@aol.com" <jonisaacs@aol.com>
    wrote:


    Why? Focal ratio tells you nothing about the exposure times. All you
    care about is the S/N, which is independent of focal ratio.

    _________________________________________________

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

  9. #9
    jonisaacs@aol.com's Avatar
    jonisaacs@aol.com Guest

    Default Planetary imaging with fast Newtonian

    Why? Focal ratio tells you nothing about the exposure times. All you
    care about is the S/N, which is independent of focal ratio.
    ----------

    It seems to me that the camera is what determines the N and the scope
    what determines the S. An 12 inch scope operating at 6000mm will
    provide more S than an 8 incher operating at 6000mm..

    I would be interested in learning why the exposures operating my Pronto
    at 6000mm FL would be the same as my 12.5 inch Newt operating at 6000mm
    FL. Somehow it just doesn't make sense to me.

    Jon


  10. #10
    RMOLLISE's Avatar
    RMOLLISE Guest

    Default Planetary imaging with fast Newtonian


    Chris L Peterson wrote:


    OK, Chris, let me restate that...

    "Image. Must make bigger." ;-)

    Peace,
    Rod


 

 
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