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Dob upgrade?

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  • Szalma Zsolt
    I am about to make some upgrades to my new 8 GS Dob. Among these are replacing the small finder with the 8x50 finder, and getting a good barlow, probably the
    Message 1 of 8 , Aug 1, 2005
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      I am about to make some upgrades to my new 8" GS Dob. Among these are
      replacing the small finder with the 8x50 finder, and getting a good
      barlow, probably the TeleVue 2x. The problem is that the scope will most
      likely be nose-heavy after these uprgades. Now, I could buy special
      magnets to balance things out, but I still wonder...since I plan to get a
      few premium eyepieces along the way (and those oculars are heavy beasts),
      isn't this uprgade an overkill for a little 8" Dob? I already installed an
      extension tube into the focuser, so that all my eyepieces can reach focus.
      Now I am about the add a bigger finder, a long barlow, and later on heavy
      eyepieces. I wonder how serious the balance problem will be. I don't feel
      like ending up with several magnets sitting on the tube. Not to mention
      that putting a barlow and a big eyepiece into the focuser, and the eyelens
      gets too far from the tube and the focusing knobs. Is it comfortable to
      use such a setup?
      So, anyone who tried such upgrades (especially the long barlow+heavy
      eyepiece combo) in a Dob like mine, please let me know about the pros and
      cons!

      By the way, this upgrade will hurt my wallet big time. But the blame is on
      RBT, who suggested (in Astronomy Hacks) that one is much better of with a
      few premium eyepieces and a good barlow than with several so-so ones. I
      beleived him, and now look...I am going straight down the slope. :-) Great
      book Robert!! I will write a review very soon.

      Thanks a lot,

      Zsolt Szalma
      (Hungary)
    • Gene Baraff
      Szalma, I ll offer some suggestions, but they are based on my perception that you have recently graudated from school and have not been working long enough to
      Message 2 of 8 , Aug 1, 2005
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        Szalma,

        I'll offer some suggestions, but they are based on my perception
        that you have recently graudated from school and have not been
        working long enough to have accumulated a big chunk of discretionary
        disposable savings. If my understanding of the Hungarian economy
        is wrong and you have, in the meantime, already become a successful
        capitalist, you may want to follow a different approach than what I
        am about to recommend.

        Remarks interspersed below.

        Gene
        ***********

        --- In skyquest-telescopes@yahoogroups.com, "Szalma Zsolt"
        <zsolo@m...> wrote:
        > I am about to make some upgrades to my new 8" GS Dob. Among these
        are
        > replacing the small finder with the 8x50 finder, and getting a good
        > barlow, probably the TeleVue 2x. The problem is that the scope
        will most
        > likely be nose-heavy after these uprgades. Now, I could buy special
        > magnets to balance things out, but I still wonder...since I plan
        to get a
        > few premium eyepieces along the way (and those oculars are heavy
        beasts),
        > isn't this uprgade an overkill for a little 8" Dob?
        . **********
        Yes, the scope IS likely to be nose heavy. But premium eyepieces
        do not have to be THAT heavy. I use Radians, which many will
        consider premium, because of my need for the eyerelief (I need
        eyeglasses to observe) and a reasonably wide AFOV. They are of a
        moderate weight. I also use magnets - happily - and find that
        they can be placed so as to achieve balance w.r.t both axes -
        something thaqt you must do if you want your scope to be in balance
        all the way from zenith to horizon. And they do this without
        marking up the exterior. We can talk about magnet choices,
        placement, suppliers and modes of use later, if you are so inclined.
        *************

        I already installed an
        > extension tube into the focuser, so that all my eyepieces can
        reach focus.
        > Now I am about the add a bigger finder, a long barlow, and later
        on heavy
        > eyepieces. I wonder how serious the balance problem will be. I
        don't feel
        > like ending up with several magnets sitting on the tube. Not to
        mention
        > that putting a barlow and a big eyepiece into the focuser, and the
        eyelens
        > gets too far from the tube and the focusing knobs. Is it
        comfortable to
        > use such a setup?
        ********
        The long Barlow does not push the eyepiece out farther than the
        short Barlow. Instead, it allows the Barlow lens to sit closer to
        the secondary mirror than does the shorty.

        The long Barlow, the Radians, and even my digital camera (which is
        held by a homemade holder that grasps the outer end of a Radian
        eyepiece) have put no excessive strain on my focusser, which is the
        stock item supplied with the GS XT10.

        ***************

        > So, anyone who tried such upgrades (especially the long
        barlow+heavy
        > eyepiece combo) in a Dob like mine, please let me know about the
        pros and
        > cons!
        **********
        Coming back to the balance (magnet) issue: I was forced to
        rebalance my scope because, in addition to the 9 x 50 Raci finder
        and Telrad installed on the upper end, I had removed the heavy metal
        plate that covered the lower end of the primary on the earlier G.S.
        XT scopes. That plate was a thermal reservoir and had to go.
        While it WAS possible to add enought friction via the springs to
        keep the scope in place, I preferred the feeling of less friction
        and a balanced scope, and - to this day - I never attach the springs
        to increase the altitude friction. At most, I add or remove a
        magnet or slide it forwards or back when making a radical change in
        the equipment I am hanging on the focusser.
        ************
        >
        > By the way, this upgrade will hurt my wallet big time. But the
        blame is on
        > RBT, who suggested (in Astronomy Hacks) that one is much better of
        with a
        > few premium eyepieces and a good barlow than with several so-so
        ones.
        *********
        While I have never used a TV 2x Barlow, I do have the Celestron
        Ultima 2x (shorty) Barlow and the Orion Ultrascopic 2x (long)
        Barlow. I see no difference in clarity and contrast between the
        two, and would have been fully satisfied with either one. My
        reasons for having and using two - a long and a short - have to do
        with other things I am interested in. Perhaps you can save
        yourself a few zlotys (or whatever the current Hungarian currency
        unit is) by choosing the Clestron ( = the Orion Shorty PLUS) or the
        Orion Ultrascopic, instead of the Televue Barlow.

        Another eyepiece, one I consider premium but that is relatively
        inexpensive and which works well for me, is the TV 32mm Plossl.
        ********

        > I beleived him, and now look...I am going straight down the
        slope. :-) Great book Robert!! I will write a review very soon.
        >
        > Thanks a lot,
        >
        > Zsolt Szalma
        > (Hungary)
      • Szalma Zsolt
        Gene, Thank you very much for your answer. You gave me lots of sound advice. ... You remember well. I just got out of university and haven t started working
        Message 3 of 8 , Aug 1, 2005
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          Gene,

          Thank you very much for your answer. You gave me lots of sound advice.

          > If my understanding of the Hungarian economy
          > is wrong and you have, in the meantime, already become a successful
          > capitalist, you may want to follow a different approach than what I
          > am about to recommend.

          You remember well. I just got out of university and haven't started
          working yet. It's not so easy to get a decent job with a freshly obtained
          diploma. Even though we have been big time capitalists since the changes,
          salaries aren't really up to the western standards.

          > Yes, the scope IS likely to be nose heavy. But premium eyepieces
          > do not have to be THAT heavy. I use Radians, which many will
          > consider premium, because of my need for the eyerelief (I need
          > eyeglasses to observe) and a reasonably wide AFOV. They are of a
          > moderate weight.

          You are right, I should look into the Radian line since they are the
          lightest of the premium eyepieces. I am going to a major star party this
          weekend, and I intend to look through premium eyepieces, including
          Radians. I wish Radians had a larger FOV though. A wide field is always
          welcome when you have a Dob. Also, I read some reviews on the Net that the
          Radians are not the most comfortable oculars to look through (blackouts,
          some kidney beaning - none is serious). Can you confirm or confute this?
          Do Radians barlow well?

          > Coming back to the balance (magnet) issue: I was forced to
          > rebalance my scope because, in addition to the 9 x 50 Raci finder
          > and Telrad installed on the upper end, I had removed the heavy metal
          > plate that covered the lower end of the primary on the earlier G.S.
          > XT scopes. That plate was a thermal reservoir and had to go.

          There was no such plate in my scope. I think GS removed them for good. I
          heard they used to slow down the cooling process.


          > While I have never used a TV 2x Barlow, I do have the Celestron
          > Ultima 2x (shorty) Barlow and the Orion Ultrascopic 2x (long)
          > Barlow. I see no difference in clarity and contrast between the
          > two, and would have been fully satisfied with either one.

          I heard good things about the Celestron Ultima barlow too. But since I
          read Robert's book, I have been reluctant to get a shorty barlow. By the
          laws of pysics, a shorty must be inferior to a standard barlow, he says. I
          am sure he's right, but the question is: can you tell the difference at
          the eyepiece? Does it cause vignetting? Is the image inferior to a long
          barlow? By the way. Here is the setup I have in mind if I choose the
          Radians: 14mm ocular, 10mm ocular and a good quality 2x barlow. This would
          give me: 86x, 120x, 172x and 240x. And if I choose the LVWs: 17mm ocular,
          13mm ocular and a good 2x barlow, giving me: 71x, 92x, 142x and 184x. I
          already have a 32mm Plossl as a low power finder eyepiece. Later on I
          could get a 30mm GS Superview or maybe a 27mm Pan. Which line would I be
          better of with? The Radian or the LVW? LVWs are cheaper, have larger FOv,
          but they are also heavier and more difficult to obtain them. You know,
          Orion just won't ship outside North America. :(

          > Perhaps you can save
          > yourself a few zlotys (or whatever the current Hungarian currency
          > unit is) by choosing the Clestron ( = the Orion Shorty PLUS) or the
          > Orion Ultrascopic, instead of the Televue Barlow.

          Our currency is still forint. One dollar is worth about 200 forints. We'll
          convert to euros in a few years. The Orion barlows are nice, but I can't
          order directly from Orion because of their shipping policy. Celestron
          seems to be the way to go, or TeleVue.

          Thank you again,

          Zsolt
          (Hungary)
        • Gene Baraff
          ... that the ... (blackouts, ... this? ... There are other eyepieces with a larger field of view. So the radian 60 degree AFOV IS a compromise - FOV costs
          Message 4 of 8 , Aug 1, 2005
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            --- In skyquest-telescopes@yahoogroups.com, "Szalma Zsolt"
            <zsolo@m...> wrote:
            > I wish Radians had a larger FOV though. A wide field is always
            > welcome when you have a Dob. Also, I read some reviews on the Net
            that the
            > Radians are not the most comfortable oculars to look through
            (blackouts,
            > some kidney beaning - none is serious). Can you confirm or confute
            this?
            > Do Radians barlow well?
            > *********
            There are other eyepieces with a larger field of view. So the
            radian 60 degree AFOV IS a compromise - FOV costs money - , but one
            which is well worth it. I find that they do barlow well, and have
            no kidney-beaning or vignetting issues.
            > ***********
            > I heard good things about the Celestron Ultima barlow too. But
            since I
            > read Robert's book, I have been reluctant to get a shorty barlow.
            By the
            > laws of pysics, a shorty must be inferior to a standard barlow, he
            says. I
            > am sure he's right, but the question is: can you tell the
            difference at
            > the eyepiece?
            > **********
            I bought my Ultrascopic after having read that statement in RBT's
            book as well. I found the view through it to be so similar to what
            I was getting in the Celestron Ultima 2x (shorty) that I would have
            returned it if I had not needed a long focus barlow for other
            independent reasons. I'll have to re-read RBT's reasons for
            preferring the long Barlow. Somehow, attributing the difference to
            the "laws of Physics" seems a bit of an overstatement to me.

            I am not able to answer the questions you have raised in the
            continuation of your post below. You might want to look at my other
            comments (tucked away in today's postings) on eyepieces. I've
            checked, and both your Radian choice and my Radian recommendation DO
            fall within the parameters Phil Lefevre posted in the file RE
            recommended.

            Gene
            ***********

            Here is the setup I have in mind if I choose the
            > Radians: 14mm ocular, 10mm ocular and a good quality 2x barlow.
            This would
            > give me: 86x, 120x, 172x and 240x. And if I choose the LVWs: 17mm
            ocular,
            > 13mm ocular and a good 2x barlow, giving me: 71x, 92x, 142x and
            184x. I
            > already have a 32mm Plossl as a low power finder eyepiece. Later
            on I
            > could get a 30mm GS Superview or maybe a 27mm Pan. Which line
            would I be
            > better of with? The Radian or the LVW? LVWs are cheaper, have
            larger FOv,
            > but they are also heavier and more difficult to obtain them. You
            know,
            > Orion just won't ship outside North America. :(
            >
          • rapideye.geo
            ... See Gene - you re so good at this stuff, you make the right choices without even knowing why - its just second nature for you =-) In all seriousness, when
            Message 5 of 8 , Aug 1, 2005
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              --- In skyquest-telescopes@yahoogroups.com, "Gene Baraff"
              <g2baraff@c...> wrote:
              > I've checked, and both your Radian choice and my Radian
              > recommendation DO fall within the parameters Phil Lefevre
              > posted in the file RE recommended.

              See Gene - you're so good at this stuff, you make the right choices
              without even knowing why - its just second nature for you =-)

              In all seriousness, when I read that file a year ago, it pulled a lot
              of the fog away for me in EP selection - just plain, good, simple,
              common sense approach.

              There is something about that 2-3mm Exit Pupil that makes it sooooo
              comfortable to use. Toss in good eye relief and you've got an EP you
              can use for hours on end with little or no eye strain.

              <RE>
            • Gene Baraff
              ... lot ... That s the reason I took Phil s post from our archives and copied it up into our files section. BTW, speaking of Phil Lefever who is one of the
              Message 6 of 8 , Aug 1, 2005
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                --- In skyquest-telescopes@yahoogroups.com, "rapideye.geo"
                <RapidEye@B...> wrote:
                >> In all seriousness, when I read that file a year ago, it pulled a
                lot
                > of the fog away for me in EP selection - just plain, good, simple,
                > common sense approach.
                >
                > ***********
                That's the reason I took Phil's post from our archives and copied it
                up into our files section. BTW, speaking of Phil Lefever who is one
                of the moderators of this group: I have not seen any postings by him
                for a long time now, and have sent him a note inquiring about how (or
                perhaps where) he is, hoping that all is OK with him. Anybody been
                in touch with him recently and can verify that he is, in fact, OK?

                Gene
                >
              • Robert Bruce Thompson
                ... How about the laws of optics ? Like short focal ratio refractors, shorty Barlows have to bend the light at tighter angles. This has several implications:
                Message 7 of 8 , Aug 1, 2005
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                  Gene Baraff wrote:

                  > I bought my Ultrascopic after having read that statement in RBT's
                  > book as well. I found the view through it to be so similar to what
                  > I was getting in the Celestron Ultima 2x (shorty) that I would have
                  > returned it if I had not needed a long focus barlow for other
                  > independent reasons. I'll have to re-read RBT's reasons for
                  > preferring the long Barlow. Somehow, attributing the difference to
                  > the "laws of Physics" seems a bit of an overstatement to me.

                  How about "the laws of optics"?

                  Like short focal ratio refractors, shorty Barlows have to bend the light
                  at tighter angles. This has several implications:

                  1. Vignetting. All other things equal, a shorty Barlow is much more
                  prone to vignetting than a full-length model, particularly when used
                  with a long focal length eyepiece.

                  2. Excessive eye relief. All Barlows extend eye relief for most simple
                  eyepiece designs, including Ploessls, but shorty Barlows exhibit this to
                  a much larger extent than full-length models. Unfortunately, the amount
                  of eye relief added is proportional to eyepiece focal length, rather
                  than inversely proportional, which would actually be helpful. When used
                  with a 32mm Ploessl or similar eyepiece, a shorty Barlow extends eye
                  relief so much that it can be hard to get and hold the exit pupil.

                  3. Lateral color. Again, with many simple eyepiece designs, a shorty
                  Barlow adds noticeable lateral color. So does a standard Barlow, but not
                  nearly as severely, assuming equal optical quality.

                  I suspect you didn't notice much difference because you were using the
                  two Barlows with your Radians, which of course are already Barlowed. Try
                  them both with a long Ploessl and see what you think.

                  --
                  Robert Bruce Thompson
                  thompson@...
                  http://www.ttgnet.com/thisweek.html
                  http://forums.ttgnet.com/ikonboard.cgi
                • Gene Baraff
                  ... RBT s ... what ... the ... Barlowed. Try ... RBT You may (as is usually the case) be on to something here. I WAS comparing the two Barlows (regular and
                  Message 8 of 8 , Aug 1, 2005
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                    --- In skyquest-telescopes@yahoogroups.com, Robert Bruce Thompson
                    <thompson@t...> wrote:
                    > Gene Baraff wrote:
                    >
                    > > I bought my Ultrascopic after having read that statement in
                    RBT's
                    > > book as well. I found the view through it to be so similar to
                    what
                    > > I was getting in the Celestron Ultima 2x (shorty) that I would >
                    > have
                    > > returned it if I had not needed a long focus barlow for other
                    > > independent reasons. I'll have to re-read RBT's reasons for
                    > > preferring the long Barlow.
                    > > *************
                    RBT replied:
                    > I suspect you didn't notice much difference because you were using
                    the
                    > two Barlows with your Radians, which of course are already
                    Barlowed. Try
                    > them both with a long Ploessl and see what you think.
                    >
                    > ***********
                    RBT

                    You may (as is usually the case) be on to something here. I WAS
                    comparing the two Barlows (regular and shorty) only in front of the
                    Radians. It never occured for me to put them in front of the TV 32
                    Plossl because long ago (when I owned only the shorty) I tried it
                    with the Plossl, and so disliked the results that I never thought
                    about Barlowing that eyepiece again. At that time, I didn't know
                    WHY I didn't like the result, but I didn't like it.

                    Now, prodded bny your comments, I'll try the 32mm Plossl with the
                    regular Barlow, and if your reasoning is correct, I'll be in a
                    position to see for myself. Perhaps, ending up thereby with a 16mm
                    lens which would do an even better job of satisfying one of Phil
                    Lefever's criteria.

                    As to the other issues you mentioned, vignetting, excessive eye
                    relief and lateral color, I'll make it a special point to seek out
                    those differences in front of the Radians. As I told Szolt, I had
                    not been consicous of them before. At this point, I have no idea
                    of what to expect, but (if the weather clears around here enough for
                    me to try it) I'll report back my own experiences to the group.
                    Perhaps Szolt can defer a decision to spend his money until I - and
                    hopefully others - report back on this issue. There may be - as
                    you point out - exceptions to your general statement w.r.t. specific
                    eyepieces that - were he to take advantage of them, could end up
                    saving him some florints.


                    Gene
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