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22422Re: Televue Binoviewers and GT81FD

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  • Timm B
    Aug 12, 2013
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      Hi Roger,

      Just to be clear, I have the GTF102 not the GTF81. I didn't have any issue reaching focus with the 2" eyepiece I have, using a 2" WO dielectric diagonal.

      When using 1.25" eyepieces, and a 2" WO dielectric diagonal, the additional insert (2" to 1.25") is needed. This adds the extra length that might push some 1.25" eyepieces outside of the focus range. With 2" eyepieces you don't need the insert, but remember not all eyepieces focus at the same spot. Why? Because some eyepiece designs shift the focus point slightly due to the extra glass inside them.

      Perhaps other here who have the GTF81 can comment on it for visual use, but it should be an excellent choice and has the added advantage of the flattener built in for sharp wide field views, and will be ready for taking astrophotos if you ever pursue that part of the hobby.

      Timm

      --- In William-Optics@yahoogroups.com, "twinklescope" <twinklescope@...> wrote:
      >
      > Hi Timm; I'm Roger and I'm new to the group. I'm just a visual
      > observer not into AP yet. I was considering the GTF 81 because it
      > seems like a quality scope and it come with a 2" focuser. I use 2"
      > eyepieces exclusivly, panoptics, naglers and explore scientific.So,
      > perhaps I should consider another scope with a focus point more suitable
      > to my eyepieces ?
      > Thanks, Twinklescope
      > --- In William-Optics@yahoogroups.com, "Timm B" wrote:
      > >
      > > Hi Paul,
      > >
      > > The GTF102 that I have is similar in that it was optimized to be used
      > for astrophotography so that the focuser wouldn't need a long extension
      > for cameras.
      > >
      > > For visual use, you will probably need a 1.25" diagonal, any will do,
      > but get a good dielectric like the WO one, and you will be happy. A 2"
      > diagonal will push the eyepiece out much further in the optical path,
      > and may not be able to reach focus.
      > >
      > > The trade off is that you will be able to easily reach focus with any
      > camera. For your DSLR you will need a 2" photo adapter with the proper
      > T-Ring attached. I like the one WO sells, but any other will work,
      > which adds enough length to allow it to reach focus.
      > >
      > > I have the iEQ45 as well, and its my first GEM so its a bit of a
      > learning curve for me, and with the long days right now I can really
      > only get it out on weekends, and we haven't had many clear Fri or Sat
      > night this summer. Look for the iOptron Yahoo groups and join them as
      > well
      > >
      > > The binoviewer issue is related. Many refractors are too long to
      > allow for the much longer optical path introduced by a binoviewer, so
      > adding the barlow in front of it will sometimes help. The hitch is
      > that you will definitely need that 1.25" diagonal, and even with that it
      > still might not reach focus. I don't have a binoviewer, so I can't say
      > for sure.
      > >
      > > If you need any help just let us know here, and we will try to help
      > you as best we can.
      > >
      > > I'm almost done with a full review of the GTF102, and will post it
      > here and on CloudyNights.com as soon as I can.
      > >
      > > Take care,
      > >
      > > Timm
      > >
      > >
      > >
      > > --- In William-Optics@yahoogroups.com, "pgabura" psg@ wrote:
      > > >
      > > >
      > > > My appologies, I forgot to introduce myself. I am new to the group.
      > I have been using a 10" Orion Dob for a few years and have a Celestron
      > 6" SCT but this is my first purchase of a refractor. I want to get into
      > astrophotography and was impressed with the sharp image and fast wide
      > field performance of the WO short FL refractors.
      > > >
      > > > Based on research I decided to buy the GT81 to start on. I also have
      > the FLT 132 on order and the iOptron iEQ45 mount.
      > > >
      > > > From reading other posts I have learned I should get the WO 2" tube
      > for my T-ring and that Binoviewers are in general dificult to use on
      > many telescopes. Perhaps these are the only answers available. Any
      > additional insite would be greatly appreciated.
      > > >
      > > > Thanks
      > > >
      > > > Paul
      > > > --- In William-Optics@yahoogroups.com, "pgabura" wrote:
      > > > >
      > > > > I was disapointed to find that the Televue Binoviewer, even with
      > the special barlow lens that comes with the viewer, cannot reach focus
      > with the GT81.
      > > > >
      > > > > It seems like an odd design of focuser as all of my eypieces seem
      > to focus within about 1/4 of the focusers travel. I have used it with a
      > Televue Panoptics 27mm and Explore Scientific 15mm and 6.7mm. What would
      > the remaining 3/4 of travel be used for?
      > > > >
      > > > > The only other eypiece I have had problems with is the Baader
      > Planitarium 8-24 zoom lens which kind of reaches focus but only at
      > maximum travel into the scope jammed up against the focuser body.
      > > > >
      > > > > I have also been unable to get focus on my Nikon D600 FX sensor
      > DSLR. I have tried it with various lengths of 1.25" tubes with no luck.
      > You can't crank the focuser in far enough.
      > > > >
      > > > > I have tried it both with and without the WO 2" diagonal.
      > > > >
      > > > > Am I doing something wrong? Have others had any difficulty
      > obtaining focus with this telescope?
      > > > >
      > > >
      > >
      >
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