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  1. #1
    Jason's Avatar
    Jason Guest

    Default Fork Mounts, Equatorial Wedges & Astrophotography?



    Hey all, I've been looking at the variety of scopes out there with an alt-az
    fork mount, and available equatorial wedge (like the Meade
    EXT-70/90/105/125, similar models from Celestron, etc.)

    Now, my understanding is that one big problem with alt-az mounts that track
    is for long-exposure astrophotography - while it will follow the rotation of
    the target around Polaris, it won't deal with the image appearing to revolve
    in the viewfinder, and therefore creating a streaking affect on film. Is
    this something that using an equatorial wedge will take care of?

    From what I've read, the equatorial wedge allows these scopes to rotate only
    on their azimuth, removing the need to change their elevation on their
    "altitude" axis. Are they basically being set up so they're on the same
    plane as the objects you're observing? If so, are they then viewing that
    target as if it were moving in a straight line across the sky, with no
    apparent revolution?

    Basically, here's the deal. I'm fairly new to astronomy, and
    astrophotography, and was considering picking up something with a better
    aperture than the 50mm f/1.7 camera lens I've been using on the Maxxum 5 I
    recently picked up. While it's a pretty decent lens, it only has a 29mm
    maximum aperture. While wide-field images of a few seconds are pretty easy
    to do (I've got some older ones with an X-700 up on my site, but I've got
    some better ones I took with the Maxxum waiting to be scanned), getting
    narrower fields of view and better magnification isn't really workable with
    my current setup, which my eclipse photos show pretty handily - the moon is
    tiny, because I had only 100mm of focal length.

    So, my goals are something with better light gathering, that might help me
    image some of the really faint objects out there. Tracking would be nice,
    to get star fields without star trails, and maybe get things like nebulas,
    galaxies, etc. Some level of magnification would be nice, when I'm trying
    to take pics of the planets, or the Moon, etc.

    My price range basically sucks at the moment. I can probably spring up to,
    oh, $300 or so over the next couple months. More than that, and we're
    talking 1-2 months additional per $100. I understand this means I won't
    have the best gear out there. Heck, I'm looking at tepid, mediocre gear,
    most likely. I understand and accept that - this isn't going to be the last
    scope I buy, and financial issues will not be an issue forever - a year or
    two from now, $1000-$2000 for a rig probably won't concern me.

    So, my options:

    First, would be something like the EXT-90, waiting a couple of extra months
    or so to do that. This is where that whole equatorial wedge combined with a
    fork mount comes into play.

    Next would be something similar to the Celestron Firstscope 114EQ. Of
    course, I've never used a German equatorial before, so I'm not sure how the
    learning curve is. For one thing, what do you do when the majority of the
    things you want to look at are in the opposite direction from Polaris?
    Example: most times I have available to observe, Orion or the Pleiades (two
    of my favorites to look at), aren't near Polaris - I'd have to point the
    scope in the opposite direction.

    Now, option three is just....weird. Anyone have any experience with Rubinar
    lenses or telescopes (examples here:
    http://www.rugift.com/photocameras/m...ras_lenses.htm and also
    here: http://www.lzos.ru/tovnp/teles/teleng.htm) - they make 1000 mm focal
    length f/10 and 500 mm focal length f/5.6 Maksutov-Cassegrain lenses that,
    with an adaptor, will fit my camera easily. Both have available adaptors to
    let you hook up eyepieces and use them as telescopes. Combine one with a
    German equatorial from Orion, for example, a motor for tracking, etc, and I
    can get a scope with halfway-decent magnification and a tracking mount for a
    good price. Of the two, I'd lean more towards the 500mm, even though it's a
    bit smaller in aperture, because it'd also work well in daylight as a
    supertelephoto lens for my camera, whereas the 1000mm is a bit too big for
    that. This option's nice because I can do it piecemeal, and get out the
    door at a fairly low price.

    OK, I think I've gone on long enough. Any advice would be welcome.

    --Jason
    http://www.websown.com/~jdonahue/astro/astrophoto.htm



  2. #2
    Roger Hamlett's Avatar
    Roger Hamlett Guest

    Default Fork Mounts, Equatorial Wedges & Astrophotography?


    "Jason @websown .com>" <jdonahue<antispamantispam> wrote in message
    news:vru9lg7n8ml428@corp.supernews.com...
    alt-az
    track
    of
    revolve
    Yes.

    only
    The terms are Ra and Dec, when equatorially mounted. Technically, the
    equatorial wedge, is to my mind a misnomer. It is really a 'polar wedge'
    (this is why you refer to such mountings as polar aligned). If you imagine
    that you are standing on the Earth, exactly at the true (not magnetic) North
    pole. Here you are standing 'on' the axis about which the planet revolves
    (remember the skies apparent motion, is being created by the world rotating,
    not any 'real' motion up there). Hence if you now put a clock flat on the
    ground, and set it to turn one revolution in each sidereal day (about four
    secods faster than a normal clock), it's hour hand, will remain pointing at
    exactly the same point in the sky, with no other motion being needed. Put an
    angled pointer on the hour hand, and aim it at a star, and again the pointer
    will remain correctly aimed as the night passes.
    This is the basis of wedge aligning. The scope is mounted at an angle, so
    it's base is parallel to the equator (or as if it was sitting on a flat
    table at the North pole). Mounted like this, the motion to match the stars,
    is rotation on the Ra axis, while the one needed to point to different parts
    of the sky, is the Dec axis.

    easy
    with
    is
    to,
    last
    months
    a
    the
    (two
    Rubinar
    to
    I
    a
    a
    Realistically, I'd avoid any of the scopes you mention for photography...
    The problem is that to take good pictures, requires the mount to be _very_
    rigid. Most of the cheaper scopes do not approach this requirement, even
    remotely (one 'rule of thumb', is to halve the useable load on a mount for
    photography). You can take photographs through these scopes, but trying to
    take even slightly longer exposure astophotographs, will leave you
    screaming.
    One of the best 'small' mounts, in terms of the accuracy of it's gears, is
    the Vixen GP-DX mount. Start by being prepared to go 'second hand', and see
    if you can obtain one of these. Add a tracking motor, and then even with
    your current lens, be amazed at how much 'deeper' your images can go,
    showing widefield features superbly.
    Going 'longer' with the lens, then allows more detail to be seen, but adds
    its own problems. The first is that many camera lenses, will show
    significant chromatic aberration on astronomical objects. Catadioptic lenses
    have less problems in this regard than refractor designs. The second link
    you give, shows a lens that might well take some quite reasonable pictures.
    However another problem then rears it's ugly head. No mount is perfect.
    Unless the telescope is absolutely accurately aligned, and the mount is
    perfect, as exposure times, and focal lengths increase, faults in the
    tracking will start to appear on the pictures. The 'solution' to this, is to
    guide the camera. With this, some light (either using an 'OAG', a prism that
    steals a small amount of light from the edge of the field of view), or a
    seperate 'guide' telescope attached to the same mount, is fed to either a
    small CCD camera, with software to guide the scope, or to an eyepiece, with
    an illuminated crosshair, allowing the photographer to apply the tiny
    'tweaks' needed for perfect guiding. So you need to consider how you are
    going to guide, as part of the system.
    If there is an astronomy club near you, it'd be well worth going along.
    Firstly, sometimes old equipment will be for sale. Secondly, you may well
    find that you can try some of the systems and techniques before spending
    money, and save a lot of waste...
    It is worth saying, that there are some very 'budget' solutions,if you are
    at all mechanically minded. Do a web search for 'barn door tracker'. This is
    a system using a hinged board, operated by a motor, that can be built for a
    very few dollars, and allows reasonable duration photography at medium focal
    lengths (don't try pushing up to 1000mm, without guiding - 200mm is a more
    reasonable scale). If you can build one of these, combined with a slightly
    longer focal length lens, you may be suprised at just how good the images
    look. :-)

    Best Wishes



  3. #3
    Kilolani's Avatar
    Kilolani Guest

    Default Fork Mounts, Equatorial Wedges & Astrophotography?

    Just my 2 cents worth.

    If your budget starts at $300, you might want to put the kaibosh on the
    astrophotography plan. In my experience astrophotography is similar to the
    classic definiton of a boat, "a hole in the water you pour money into."

    "Jason @websown .com>" <jdonahue<antispamantispam> wrote in message
    news:vru9lg7n8ml428@corp.supernews.com...


    *snip*

    to,

    You said you are new to astronomy... I recommend you get yourself a decent
    aperture (6-8") Dob (fairly close to your $300 budget) and spend the next
    year or two learning the sky... then when you have (multi) thousands of $ to
    spend, you can play astrophotography.



  4. #4
    MDJ's Avatar
    MDJ Guest

    Default Fork Mounts, Equatorial Wedges & Astrophotography?

    If you can, go for an Orion (US not UK) ED80mm refractor. This is of
    excellent quality but there is a waiting list. Look for Orion ED80 on Google
    to get some reviews.

    MarkDJ


    "Jason @websown .com>" <jdonahue<antispamantispam> wrote in message
    news:vru9lg7n8ml428@corp.supernews.com...
    alt-az
    track
    of
    revolve
    only
    easy
    with
    is
    to,
    last
    months
    a
    the
    (two
    Rubinar
    to
    I
    a
    a


    ---
    Outgoing mail is certified Virus Free.
    Checked by AVG anti-virus system (http://www.grisoft.com).
    Version: 6.0.543 / Virus Database: 337 - Release Date: 21/11/2003



  5. #5
    Michael A. Covington's Avatar
    Michael A. Covington Guest

    Default Fork Mounts, Equatorial Wedges & Astrophotography?


    "Jason @websown .com>" <jdonahue<antispamantispam> wrote in message
    news:vru9lg7n8ml428@corp.supernews.com...
    alt-az
    track
    of
    revolve

    Exactly. That's its purpose.

    With an equatorial wedge, the telescope rotates around only one axis, which
    is parallel to the earth's axis. All parts of the telescope remain in the
    same orientation relative to the stars as the rotation proceeds.

    Let me suggest a couple of books (which I happen to have written) -- How to
    Use a Computerized Telescope (which covers astrophotography briefly, along
    with other telescope details) and Astrophotography for the Amateur. A few
    dollars spent on a book can save you hundreds on equipment.


    --
    Clear skies,

    Michael Covington -- www.covingtoninnovations.com
    Author, Astrophotography for the Amateur
    and (new) How to Use a Computerized Telescope




  6. #6
    Alan W. Craft's Avatar
    Alan W. Craft Guest

    Default Fork Mounts, Equatorial Wedges & Astrophotography?

    On Sat, 22 Nov 2003 01:07:34 -0800, "Jason" <jdonahue<antispam>@websown<antispam>.com> ...reflected:

    <snip>


    That's precisely the beauty and attraction of the German Equatorial
    Mounting(GEM), for with it you may point any telescope mounted thereupon
    anywhere.

    <snip>

    Alan

  7. #7
    Stephen Paul's Avatar
    Stephen Paul Guest

    Default Fork Mounts, Equatorial Wedges & Astrophotography?

    "Jason @websown .com>" <jdonahue<antispamantispam> wrote in message
    news:vru9lg7n8ml428@corp.supernews.com...

    Jason,
    Lunar imaging can be done on the cheap using a webcam like the Philips
    ToUcam Pro. It doesn't take a lot of telescope, or a super accurate mount to
    do this either. Planets can also be imaged with these little wonders if you
    are willing to put the time into processing the webcam's output via
    software.

    For the moon, the 400mm focal length of a Short Tube 80 is probably
    sufficient, but planets require more in the range of 5000mm for increased
    image scale. (Photographically, 50mm = 1x, so 400mm = 8x what youl'll get
    out of the 35mm lens, and 5000mm = 100x).

    For imaging solar system objects, the issue with tracking is in keeping the
    target on the detector (which can be a challenge at 5000mm focal length).
    However, one of the beauties of the webcam is that you get a live image on
    the computer display, so as long as you have a handcontroller for your
    mount, you can manually keep the target in view while the AVI file is being
    created.

    The key here is that solar system objects are bright enough that a 1/25th
    (and less) second exposure is enough to gather some light. The webcam
    outputs an AVI file, which can then be broken down into individual frames of
    whatever exposure setting you have chosen. This can be done using a free
    software utility like RegiStax. These frames are then separated into keepers
    and throw aways, the keepers can be stacked to accumulate goodness and build
    a detailed image. There is a time restraint on how long you can make the AVI
    file as the imaged planet is in rotation, but generally 1 minute of webcam
    output can give you a lot of frames to work with.

    When you move into deep sky imaging (not including wide field imaging of
    stars and constellations), that's a whole 'nother game for mount accuracy.

    My very first image was of the moon through my $399 Tasco Starguide 4 (4"
    F13 Mak-Cass GoTo) and a Philips webcam with a CMOS detector. I was hooked.
    I later bought a used 8" SCT and a used MX5-C astro-imaging camera (has a
    cooled CCD for long exposures), but recently I picked up a ToUcam Pro
    because frankly it's a whole lot easier to image in real time.

    Anyway, I hope this is of some help. Start small. My next step is to get an
    SLR lens for the MX5-C and a piggy-back adapter for the SCT (a fork/wedge
    setup) to try some wide field work. Wide field is also less demanding on
    mount accuracy. Most experienced imagers will tell you to start with
    piggy-back. But with the advent of webcam imaging and laptop computers, the
    moon is also a good start.

    Good luck,
    Stephen Paul


  8. #8
    Laura Halliday's Avatar
    Laura Halliday Guest

    Default Fork Mounts, Equatorial Wedges & Astrophotography?

    jonisaacs@aol.com (Jon Isaacs) wrote in message news:<20031123072525.13980.00000711@mb-m15.aol.com>...


    Do some wide-field fixed tripod shots. Spend ten bucks
    and build a barndoor tracker. The experience will
    serve you well.

    You'll get really neat pictures, and will be able to
    tell, pretty quickly, if astrophotography is for you.
    While the pictures can be wonderful, the act of actually
    taking them requires fairly serious patience.

    In other words, it's like watching paint dry, with the
    added bonus of freezing your backside off while you're
    doing it... :-)

    Laura Halliday VE7LDH "Que les nuages soient notre
    Grid: CN89mg pied a terre..."
    ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte

  9. #9
    Michael A. Covington's Avatar
    Michael A. Covington Guest

    Default Fork Mounts, Equatorial Wedges & Astrophotography?


    "Laura Halliday" <marsgal42@hotmail.com> wrote in message
    news:d42b5a72.0311251158.52a8d0b8@posting.google.c om...


    I agree wholeheartedly. That's how I got started, and it's why my book
    starts with a lot of detail on such things. With very little equipment, you
    start encountering the same technical issues and skill-building
    opportunities that you would encounter with the very biggest telescopes.
    Either you like it or you don't. And you can get beautiful pictures with
    simple equipment, particularly in the winter -- Orion is a very fine
    fixed-tripod target.

    --
    Clear skies,

    Michael Covington -- www.covingtoninnovations.com
    Author, Astrophotography for the Amateur
    and (new) How to Use a Computerized Telescope




 

 

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