Re: Optical Instruments

From: Russ Bessom (russbessom@desurf.com)
Date: Tue Sep 03 2002 - 15:18:16 EDT

  • Next message: David Brierley: "DMB Obs Aug 29"

    To all interested in buying the ETX
    I held off posting to this question but after thinking about it I decided to
    give my two cents worth regardless of whose feet I would stomp on, as I
    would appreciate the same from other list members.  Several members have
    shown an interest in purchasing one of the ETX scopes.  I had the 90 mm
    aperture scope with the recommended Meade Tripod. (tripod $200.00) ETX 90
    ($495.00).  For $700.00 total it is basically not a bad scope.  However, It
    is "IN MY OPINION, NOT SUITABLE FOR SATELLITE WORK!  If you could take the
    OTA off of the base and mount it on a stable alt/az platform of some kind,
    maybe.  But I could not figure out how to take it off.  The finder scope is
    useless!  Too close to the body of the scope, can't get your head close
    enough to see through it.  You must purchase a Rigel Quick finder or
    equivalent (places a red dot onto a piece of glass) and fabricate an
    external mount of some kind.  Now for optics!  With a focal length of 1250mm
    / F13.8 this is an extremely slow scope requiring loads of light to offset
    the central obstruction and the lack of high reflective coatings to show any
    kind of resolution.  With a 3.5" aperture, you don't get enough light to be
    remotely interesting.  The four views that this scope is good for is 1.
    Saturn, 2. Jupiter, 3. The moon, and 4. Birds.  All else, put it away, and
    grab your binoculars.  This possibly could be used for geos, but when I used
    it for such, The field of view was small and dark.  I know, just the thing
    for isolating a hard to find flasher, but again, Very hard or should I say
    uncomfortable to spend any amount of time looking in this ocular for
    flashing geos.  But you could if you wanted to.  The Meade ETX 90EC comes
    with a 26mm eyepiece which puts the power to about 48x.  IN MY OPINION This
    is just about the maximum for this scope with such a small aperture, maybe a
    20mm max and then the resolution would start to fall off.  Any higher power
    and it will be just to dark!  Read all the articles on this and you see that
    this is a kids scope.  Much better than the supermarket variety, but not for
    a professional observer or a hobbyist of any kind.  The only thing the ETX
    gives you over binos is power.  Ease of use is out the window.  I used my
    ETX for satellite observing about 3 times.  My mounted 10x50's regardless of
    what I was trying to see was more than sufficient and tons more comfortable,
    plus a much more pleasing view.  The slew rate seemed fast enough to track
    the ISS but I never tried for all the reasons above.  I used my ETX a total
    of maybe ten times and it went in the closet.  The 10x50 binos cost me
    $35.00 and I use them every time the clouds let me.  I waited so long to get
    a look at the ETX and finally in a Mall in California I got my chance.  Wow!
    Inside they were great and that motor Cool!  And the looks, Wow!  10 days,
    then in the closet.  If marketing was everything then the whole Meade line
    up would be the ultimate, ah but reality.  If you must buy a scope, I would
    recommend a good  8" scope.  I think Mike McCants has one, See how he likes
    it for satellite observing.  Anyway, get something with good light gathering
    ability that could be used for geos without the shortcomings of the smaller
    aperture scope.  As for coatings, spend the extra money and get the
    brightest aluminized coatings you can afford, remember most Schmidt
    Cassagrain and Maksutov scopes are scopes with long focal ratios.  Faster
    scopes like Paul Gabriel's 101 is what you want,  however you got to pay for
    that kind of excellence.  I am spoiled by these fast scopes, I can never own
    anything else and be happy.  It is so tough to buy a scope when you have no
    way of trying it out in dark skies.  Try very hard before you buy, to go to
    a star party and spend some time talking to the owners of these Schmidt's
    and Maks.  Find out what they use them for and why.  And also what their not
    good for!  BOTTOM LINE...TRY BEFORE YOU BUY...AND TRY MANY!  I had an Astro
    Physics 105 traveler.  Fantastic scope, but for me I wasn't happy using if
    for hunting satellites.  The mount was all wrong.  I later sold the AP105
    and bought Myauchi giant binos.  The thing that got me into giant binos was,
    at a star party in Germany I had my AP105 setup showing satellites to a
    bunch of astronomers pretty amazed at the views I was seeing, then I heard a
    person close by looking through a pair of 120mm Nikon binos shout holy sh--!
    I ran over there and said what?  He said I'm tracking a satellite, look!
    When I did, I couldn't believe my eyes.  Wow!  The field of view was so big!
    The depth perception I had was incredible, I could see stars in front of
    other stars and the satellite was in front of all the stars almost like 3D.
    The view was so bright and razor sharp.  I'll never forget that view!  It
    was so easy to move these things and so comfortable standing there naturally
    using both my eyes with stereo vision.  tracking the satellite was so
    natural!  I was hooked!  I traded a telescope dealer my AP105 for a pair of
    Myauchi binos.  The Nikons were $7000.00 and were out of my reach, so I
    settled on the Myauchis.  Not as good but still better than the 105.  I have
    since built a custom stand that holds my notebook computer and the binos
    that's a delight to use.  I am very happy with this setup.  All else pales
    in comparison.  So you see, I'm a little spoiled when it comes to comparing
    the ETX scopes with what I'm using, but remember I still reached for the
    10x50's before I would get the ETX out of the closet.
    P.S.  Still dreaming about those 120mm Nikons, ah, some day!
    
    Russ Bessom - russbessom@desurf.com
    Zweibruecken Germany
    Lat 49.14.0 N / Long 7.19.0 E - 325m
    
    
    ----- Original Message -----
    From: "Björn Gimle" <b_gimle@algonet.se>
    To: <SeeSat-L@satobs.org>
    Sent: Monday, September 02, 2002 2:58 PM
    Subject: Re: Optical Instruments
    
    
    > I think it can do 4.5 d/s in BOTH RA and Dec simultaneously, so it could
    "track"
    > (leap-frog) at a range of 100 km.
    > For orbits close to 100 km height, there would be a black-out period on
    > high-elevation transits, when az-rate exceeds 4.5, and the telescope must
    swing
    > around to acquire the satellite descending, up to 40 s later on a zenithal
    pass?
    >
    > What worries me more is the report in May 2000 S&T that the scope doesn't
    stop
    > at the correct RA/dec !
    >
    > > ...Also, has anyone done this with the Meade ETX telescope series???
    >
    > > If you look closely at the specs, I think you will find ETX telescopes
    cant
    > slew
    > > fast enough to track close passes of the ISS and other objects in
    > > similar or lower orbits. I dont know whether you can use such telescopes
    > > purely manually.
    >
    >
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