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Re: TEC 140 Focuser Question

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  • yuri80226
    ... Hi Steve, I forwarded your question to Detlef (Starlight Instrument) and he said : The 3.5 inch focuser is most likely very square relative to the
    Message 1 of 3 , Jun 1, 2003
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      --- In tec-scopes@yahoogroups.com, "sdheckenlively" <sdheckenlively@y...>
      wrote:
      > Hi Yuri,
      >
      > What is the squareness of the focuser drawtube on the TEC 140,
      > measured in thousandths of an inch?
      >
      > I just discovered the drawtube on the digital JMI NGF-S I
      > have is canted 0.010 with respect to the image plane. I
      > emailed JMI and hope they will help (its out of warranty).
      > I could hardly believe it, but its a simple measurement
      > using calipers, and I checked it several times.
      >
      > This focuser has been on the shelf many years, but I have
      > 2 JMI DX-2s also which I now will have to check. If they
      > are all hosed too, I may have to contact Starlight :-)
      >
      > The only excuse for not discovering this earlier is my own
      > naivette, and maybe over-reliance on a laser collimater.
      >
      > I believe Celestron used to make a special eyepiece for
      > checking focal plane squareness (called the MFFT?) Anyone
      > ever use it? I think maybe it used a Ronchi grating.
      >
      > Steve

      Hi Steve,
      I forwarded your question to Detlef (Starlight Instrument) and he said :
      "The 3.5 inch focuser is most likely very square relative to the mounting
      flange. Probably within a few thousands across the entire length of
      the draw tube". More info will be available later and you can contact Detlef
      yourself.
      As per JMI focuser - I assembled last one in 1993 and since than I am not in
      charge, but JMI stuff for sure will answer your question.
      regards,
      Yuri
    • sdheckenlively
      Thanks Yuri. Can I ask a follow-up question? When a scope leaves TEC, you know its good, but when we get it, we put all sorts of accessories and attachments on
      Message 2 of 3 , Jun 2, 2003
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        Thanks Yuri. Can I ask a follow-up question?

        When a scope leaves TEC, you know its good,
        but when we get it, we put all sorts
        of accessories and attachments on it.

        Could you recommend any approach for a TEC owner
        to perhaps investigate the squareness of 3rd
        party attachments? Cameras, diagonals, motorized
        focusers, etc. Is using a Ronchi grating feasible?
        Can you recommend a book that shows how to interpret
        the pattern made by a slanted focal plane?

        I am interested in correcting such problems, e.g.
        using shims, I don't want to criticize the
        makers. After looking at the JMI focuser, I am
        surprised it isn't worse. Positioning the 4 roller
        bearings accurately on a curved surface looks
        very hard, even using CNC. Why not use a square
        drawtube with a round bore, eh?

        But anyway, shim stock is cheap, and good optics deserve
        good owners :-) I'm trying, I bought a 1/10 wave window
        for my CCD, very affordable (optosigma.com), heheh.

        Steve

        --- In tec-scopes@yahoogroups.com, "yuri80226" <tec@t...> wrote:
        > --- In tec-scopes@yahoogroups.com, "sdheckenlively"
        <sdheckenlively@y...>
        > wrote:
        > > Hi Yuri,
        > >
        > > What is the squareness of the focuser drawtube on the TEC 140,
        > > measured in thousandths of an inch?
        > >
        > > I just discovered the drawtube on the digital JMI NGF-S I
        > > have is canted 0.010 with respect to the image plane. I
        > > emailed JMI and hope they will help (its out of warranty).
        > > I could hardly believe it, but its a simple measurement
        > > using calipers, and I checked it several times.
        > >
        > > This focuser has been on the shelf many years, but I have
        > > 2 JMI DX-2s also which I now will have to check. If they
        > > are all hosed too, I may have to contact Starlight :-)
        > >
        > > The only excuse for not discovering this earlier is my own
        > > naivette, and maybe over-reliance on a laser collimater.
        > >
        > > I believe Celestron used to make a special eyepiece for
        > > checking focal plane squareness (called the MFFT?) Anyone
        > > ever use it? I think maybe it used a Ronchi grating.
        > >
        > > Steve
        >
        > Hi Steve,
        > I forwarded your question to Detlef (Starlight Instrument) and he
        said :
        > "The 3.5 inch focuser is most likely very square relative to the
        mounting
        > flange. Probably within a few thousands across the entire length of
        > the draw tube". More info will be available later and you can
        contact Detlef
        > yourself.
        > As per JMI focuser - I assembled last one in 1993 and since than I
        am not in
        > charge, but JMI stuff for sure will answer your question.
        > regards,
        > Yuri
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