Loading ...
Sorry, an error occurred while loading the content.

New scope - first impressions

Expand Messages
  • Szalma Zsolt
    Yesterday I picked up my new 8 GS Dob. It is a very nice scope with metal green finish. The Crayford focuser is very smooth. There is a primary mirror fan
    Message 1 of 4 , Jul 1, 2005
    • 0 Attachment
      Yesterday I picked up my new 8" GS Dob. It is a very nice scope with metal
      green finish. The Crayford focuser is very smooth. There is a primary
      mirror fan installed in the back of the mirror cell. I haven't tried it
      yet, as I don't have 8 AA batteries at home at the moment. I wonder how
      long they would last if I turned on the fan. I don't think I'll use it
      often. Standard accessory was a 32mm SuperPlossl eyepiece which is very
      nice and comfortable to use. Unfortunatly I had to cut on the expenses (I
      need to save some money for star parties), so this time I omittedthe 2" GS
      ocular and the bigger finder. But hey, I can always add these at a later
      time.
      The base assembly was quite straightforward and took about 40 minutes.
      Unbeleivably the sky was clear last night. It was quite hazy but let's not
      be too voracious. :) Aligning the finder was a breeze, took about 30
      seconds. I take a look at Jupiter. It was nice, though the atmoshphere was
      quite turbulent. At 160x I couldn't really get a sharp focus. I try again
      tonight, maybe conditions will be better. Also, collimation needs a little
      tweak. The shadow of the secondary in the defocused Jupiter image was a
      bit off-center. I shall have a Cheshire in about a week, I'll fine tune
      the collimation then.
      I am pleasantly surprised by the little 30mm finder. It shows quite a lot
      of stars and is of good quality. I even saw M27 through it. You guys were
      right about the ease of use of a dobsonian telescope. Finding M57, M15,
      M27, Albireo was very easy. Tracking is easier than I thought too,
      although the mount is a bit tight in azimuth. I need to loosen the bolt a
      bit, and hopefully it will get smoother. Overall, I am impressed by the
      how easy this scope is to use.

      Now, what's not so great: I have a little problem with balance. The rear
      end of the tube is a bit heavier. When I remove the eyepiece the tube
      slowly swings back as the weight of the mirror pulls it down. This makes
      it hard to stay on target while exchanging eyepieces. With an eyepiece in
      the focuser this problem vanishes. I believe when I get the 50mm finder
      there'll be no more problem with balance. Till then, I have to hold the
      tube by a hand when switching oculars.

      Now, the more concerning issue. I have 5 eyepieces at the moment: one 32mm
      Plossl, and 4 Orion Epic-EDs. None of them(!) comes to focus when fully
      seated into the focuser and the focuser is racked all the way out!! All
      needs to be pulled out about 2 centimetes to reach focus. Now, one of our
      neighbors is a turner. I called him this morning and an extension tube is
      being made at this moment. This will take care of the problem, but isn't
      this only a treatment of the symptom? I mean, do you think something wrong
      could be with my scope? Did I get a defected scope? That would really turn
      me down! Maybe the focal length is a bit longer than it should be. Or what
      could be the problem? Is this something I should worry about and call the
      guy I got it from (he's also an amateur astronomer and a friend of mine)
      or should I be just happy with using the extension tube? I waited for so
      long to be able to get this scope. I surely wouldn't be thrilled by having
      to return it for repair or an exchange. That would leave me scope-less for
      weeks. :-((

      So, overall...seems to be a very nice telescope...I just need to get some
      annoying things out of the way. :)

      Clear Skies,
      Zsolt Szalma
      (Hungary)
    • Geoff Gaherty
      ... I m certain the 8 is balanced for an 8x50mm finder, which weighs a lot more than the 6x30. Try adding a bit of weight to the eyepiece end. I use Velcro
      Message 2 of 4 , Jul 1, 2005
      • 0 Attachment
        Szalma Zsolt wrote:

        > I have a little problem with balance. The rear
        > end of the tube is a bit heavier. When I remove the eyepiece the tube
        > slowly swings back as the weight of the mirror pulls it down. This makes
        > it hard to stay on target while exchanging eyepieces. With an eyepiece in
        > the focuser this problem vanishes. I believe when I get the 50mm finder
        > there'll be no more problem with balance.

        I'm certain the 8" is balanced for an 8x50mm finder, which weighs a lot more
        than the 6x30. Try adding a bit of weight to the eyepiece end. I use Velcro
        strap-on ankle/wrist weights which I bought at a hardware store.


        > I have 5 eyepieces at the moment: one 32mm
        > Plossl, and 4 Orion Epic-EDs. None of them(!) comes to focus when fully
        > seated into the focuser and the focuser is racked all the way out!! All
        > needs to be pulled out about 2 centimetes to reach focus.

        Be thankful it isn't in the other direction! I've never had any problems with
        any of my eyepieces reaching focus in any of the GS scopes I've tested. It may
        be that your mirror has a slightly longer focal length than average, which is
        not unusual in Newtonian mirrors. Another possibility is that the springs in
        your mirror cell may be a bit loose, and tightening them will bring the mirror
        further down the tube. A third possibility is that your secondary may not be
        directly under the focuser, shortening the optical path...I've seen that too.

        Geoff

        --
        Geoff Gaherty
        Toronto Centre RASC
        http://www.gaherty.ca
      • Szalma Zsolt
        ... You are probably right. If I leave the dust cap on, the balance problem disappears, indicating that only a little more front weight takes care of this
        Message 3 of 4 , Jul 1, 2005
        • 0 Attachment
          Geoff Gaherty wrote:

          > I'm certain the 8" is balanced for an 8x50mm finder, which weighs a lot
          >more than the 6x30.


          You are probably right. If I leave the dust cap on, the balance problem
          disappears, indicating that only a little more front weight takes care of
          this issue. The first thing I'm going to buy after I sell my old TAL is a
          50mm finder.

          > Be thankful it isn't in the other direction! I've never had any
          problems >with any of my eyepieces reaching focus in any of the GS
          scopes I've >tested.


          You are right. This problem can be solved at least. I was still a little
          disappointed though. I will call Lajos (the guy at Telescope-Service) and
          see what he has to say about this. Unfortunatly, he is being on vacation
          at the moment. Until he returns I'll have to live with this issue.

          > It may be that your mirror has a slightly longer focal length than
          >average, which is not unusual in Newtonian mirrors.


          If this is the case, then there's not much we can do I guess. Either I
          should opt for a replacement or use the extension tube. But if the focal
          length is longer than it should be, doesn't it mean that I can't utilize
          the whole aperture? I mean that the secondary mirror is too close to the
          primary to take up the whole diameter of the light beam.

          > Another possibility is that the springs in your mirror cell may be a bit
          >loose, and tightening them will bring the mirror further down the tube.


          How could I check this? The only springs I see in the cell are the
          collimation springs. Obviously, these are not the spring you are talking
          about. Or are they? :-)

          > A third possibility is that your secondary may not be directly under the
          >focuser, shortening the optical path...I've seen that too.


          Well, to my eyes it seems to be at the right place, but I am no expert. I
          am going to have to have someone check it for me.
          Hopefully, this issue will be solves one way or the other soon. Till then,
          I just enjoy the views this scope gives me.

          Zsolt Szalma
          (Hungary)
        • Geoff Gaherty
          ... Yes, these are the springs. They work against the collimation bolts. It may be that the bolts are quite loose, so the springs are at maximum expansion.
          Message 4 of 4 , Jul 1, 2005
          • 0 Attachment
            Szalma Zsolt wrote:
            > Geoff Gaherty wrote:
            >
            >>Another possibility is that the springs in your mirror cell may be a bit
            >>loose, and tightening them will bring the mirror further down the tube.
            >
            >
            >
            > How could I check this? The only springs I see in the cell are the
            > collimation springs. Obviously, these are not the spring you are talking
            > about. Or are they? :-)

            Yes, these are the springs. They work against the collimation bolts. It may be
            that the bolts are quite loose, so the springs are at maximum expansion. Try
            tightening all three bolts simultaneously to compress the springs. This should
            help the problem, but perhaps not enough to solve it.

            Geoff

            --
            Geoff Gaherty
            Toronto Centre RASC
            http://www.gaherty.ca
          Your message has been successfully submitted and would be delivered to recipients shortly.